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nirvanix
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Plato's challenge
      #6300475 - 01/08/14 05:24 PM

When do people think is the best time to go after Plato's craterlets? It's first quarter, so tomorrow, the day after? I had some success last year but can't remember how many days past the quarter it was?

Kind regards.


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brianb11213
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Re: Plato's challenge new [Re: nirvanix]
      #6300690 - 01/08/14 07:23 PM

About 2 days after Plato is illuminated. Friday is probably optimum for this lunation. Too low sun gives low illumination levels making it harder to pick up the small craterlets (or at least that's what I find). With sufficient optical power the main craterlets can be seen under full moon illumination as light spots.

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edosaurusrex
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Re: Plato's challenge new [Re: brianb11213]
      #6301089 - 01/08/14 11:14 PM

Here are the predicted times for the Sun altitude to be 12 degrees at Plato's center. Rising time plus a few days or setting time minus a few days should put viewing at the conditions stated in the earlier posts.

PLATO PREDICTIONS FOR 2014
MMM DD HHMM UT

JAN 10 2336 RISING
JAN 22 2214 SETTING

FEB 09 1412 RISING
FEB 21 1157 SETTING

MAR 11 0518 RISING
MAR 22 2356 SETTING

APR 09 2015 RISING
APR 21 1028 SETTING

MAY 09 1027 RISING
MAY 20 2013 SETTING

JUN 07 2331 RISING
JUN 19 0559 SETTING

JUL 07 1122 RISING
JUL 18 1629 SETTING

AUG 05 2212 RISING
AUG 17 0416 SETTING

SEP 04 0825 RISING
SEP 15 1733 SETTING

OCT 03 1841 RISING
OCT 15 0813 SETTING

NOV 02 0539 RISING
NOV 13 2345 SETTING

DEC 01 1755 RISING
DEC 13 1525 SETTING
DEC 31 0740 RISING


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Sarkikos
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Re: Plato's challenge new [Re: brianb11213]
      #6301417 - 01/09/14 07:04 AM

Quote:

With sufficient optical power the main craterlets can be seen under full moon illumination as light spots.




Yes, this is true. But sticklers will say that you're not really "seeing" the craterlets, you're only detecting their albedo spots. Personally, I'm not that persnickity.


Mike


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nirvanix
Carpal Tunnel


Reged: 06/07/07

Loc: Saskatoon, SK
Re: Plato's challenge new [Re: Sarkikos]
      #6301791 - 01/09/14 11:06 AM

Hey, thanks for the responses folks

I'm supposed to get clear skies Friday so I will give it a go. Last year I believe I got 7 recognizable and, as you say Mike, an albedo spot. I'm in your camp with regards to that - everything we see is photonic stimuli so if a set of photons causes an albedo spot to be seen then as with everything we see we have to deduce what is actually there, in this case a craterlet.

I recently got an autocollimator and after looking at the moon Tuesday night I feel that it has improved my dob collimation enough to make a difference, so I'm looking forward to going after Plato. On Tuesday I spent a good deal of time looking at the central peak of Theophilus - the illumination was such that it looked all the world like a snow-capped peak. Just beautiful.


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Sarkikos
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Re: Plato's challenge new [Re: nirvanix]
      #6301807 - 01/09/14 11:13 AM

I have a new old - as they say on "American Pickers" - C5 that I want to try out for lunar/planets/doubles ... if the skies clear up and the snow and ice melt. The number of craterlets seen in Plato would be a good test if I can catch the right night.

Mike


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nirvanix
Carpal Tunnel


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Re: Plato's challenge new [Re: Sarkikos]
      #6301841 - 01/09/14 11:31 AM

Well good luck to both of us Mike. I wonder if the American Pickers ever found a great telescope in someone's barn?

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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6303775 - 01/10/14 09:33 AM Attachment (88 downloads)

Nirv, here's an excellent guide to Plato's craters. (Source unknown)

I've managed the big 5 A through E. A through D one one night long ago and picked up E recently. Add a few others as specks, I think my own total is about 11, if memory serves including the speck count.

Good luck, it's a great challenge. The times above are nice for picking them up, maybe catch the waning moon in that seeing might be a tad better later in the night.


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nirvanix
Carpal Tunnel


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Re: Plato's challenge new [Re: Asbytec]
      #6304266 - 01/10/14 01:47 PM

Thanks Norme. I've seen A-E and g,h. Will have to try for i,j. There is no l,n, o ?

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David Knisely
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Re: Plato's challenge new [Re: Sarkikos]
      #6304318 - 01/10/14 02:07 PM

Quote:

Quote:

With sufficient optical power the main craterlets can be seen under full moon illumination as light spots.




Yes, this is true. But sticklers will say that you're not really "seeing" the craterlets, you're only detecting their albedo spots. Personally, I'm not that persnickity.


Mike




With the "white dot" albedo features, you are at the very least, "detecting" some of the craterlets. However, when the moon is not full, it takes a little more aperture (and good seeing) to resolve the craterlets and show them as the true pits they are than it does the tiny white spots that some of them generate under full moon illumination. Clear skies to you.


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Sarkikos
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Re: Plato's challenge new [Re: David Knisely]
      #6304392 - 01/10/14 02:39 PM

Quote:

With the "white dot" albedo features, you are at the very least, "detecting" some of the craterlets. However, when the moon is not full, it takes a little more aperture (and good seeing) to resolve the craterlets and show them as the true pits they are than it does the tiny white spots that some of them generate under full moon illumination. Clear skies to you.




Agreed.

Mike


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Asbytec
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Re: Plato's challenge new [Re: Sarkikos]
      #6305145 - 01/10/14 10:37 PM

Nirv, well done. That's a great craterlet count. Seems you've set the bar.

Correct me if I'm wrong, but the challenge with Plato is it's floor albedo is relatively dark making the smallest craterlets normally resolvable in craterform (rim and floor seen) by an aperture a little more difficult.

//Thinking out loud

If the rim is highly illuminated, it should stand out nicely against Plato's dark floor offering up a nice speck. However, the craterlet floor is also pretty dark, so unlike a brighter rim the contrast with Plato's floor is very small making the crater difficult to observe in true crater form. We should be able to see anything on the moon that is bright enough to create a diffraction artifact (disc) that stands out against the bright surface. This can include a crater that is the angular diameter of a point source provided its (rim is) bright enough relative to the background.

If so, then it's rim should create diffraction effect somewhere near FWHM of a point source very near Lamda/D or 113.4/Dmm. At the moon's average distance that should create an Airy disc subtending an apparent diameter of about 0.9 miles for a 6" aperture. So, to be seen then, the crater would have to be slightly larger in order for it's darker floor to be seen outside and separated from the edge of the diffraction disc formed. So, the rim has to be bright enough to form a diffraction artifact brighter than the moons surface and the floor must subtend a diameter larger than Lambda/D limit and closer to the Dawes limit.

If there is a shadow in the craterlet floor and it's diameter is at least the Dawes limit, it's contrast against the moon's brightly lit surface should remain high enough to be seen (as a bright speck and a dark speck.) The Dawes limit seems to account for the illumination of not only the rim but also the brighter moon's surface surrounding the crater floor just as it does with a nearby star.

The moon's point source brightness plays an important role, too. The moon is pretty bright even on point source scales (not sure the exact figure.) So, diffraction artifacts are both a tiny bit larger and also appear to be larger due to the eye response. However, higher magnification upwards of about 50x per inch expands and dims the image of the moon's surface. Since a point source angular diameter remains constantly small, it also dims those diffraction artifacts making them smaller in angular diameter. The surface feature, like a crater rim, is also less brilliant in terms of our eye's response. So, some high magnification is useful. It would seem while you could resolve a crater at 1mm exit pupil (being the average magnification to see an Airy disc), the moon is just too bright. In practice it might require closer to 0.5mm.

That's theory and something to shoot for in diffraction limited seeing. In practice may be more difficult. The best I've done (and very rarely) is something approaching 1 mile in diameter in excellent seeing. That's just approximately Dawes (given some slop with accuracy of measuring the diameter and with error in the moon's distance.) Plato's E crater is about 1.2 miles in diameter. Being the smallest crater form I've noted (again, rarely) within Plato, it suggests they are a bit more difficult than smaller craters against a brighter background.

Thoughts? Sorry for rambling, but the idea of seeing what can be theoretically seen is interesting. It opens up so much for us to see when we can see it.

//End thinking out loud.


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6305263 - 01/10/14 11:59 PM

Ok here's what's vexing me a bit Norme...

The gold standard for finest crater resolution per aperture has a crater half filled with light and shadow. There's a correlate to Dawes that seems to generalize a fair rule of thumb. Hence, 1.5 miles for a 6" aperture.


What happens when the craterlet is far smaller and puts fourth nothing larger than perhaps Osiris did? Say its a bright crater pit in a dark floor - nice contrast - what's the smallest of this type a 6" can resolve at least as a point source?

Think of Osiris or some of the other truly small features eeking in just under half a sec of arc.

Is it too far fetched at least in theory to suggest a 6" can *resolve*, ie; see - a craterlet perhaps .37 miles across as a singular dot?


The moment a craterlet can be seen as a veritable diffraction point through contrast - the smallest crater - 9/D would seem to be ~ a fourth of that?

You see where Im going?

Pete


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David Knisely
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Re: Plato's challenge new [Re: Asbytec]
      #6305380 - 01/11/14 01:46 AM Attachment (45 downloads)

Quote:

Nirv, here's an excellent guide to Plato's craters.

I've managed the big 5 A through E. A through D one one night long ago and picked up E recently. Add a few others as specks, I think my own total is about 11, if memory serves on the speck count.

Good luck, it's a great challenge. The times above are nice for picking them up, maybe catch the waning moon in that seeing might be a tad better later in the night.




And you have used exactly the same crater ID's that I created many years ago when I first put this article up on-line in 2003, 2005, and 2007 on sci.astro.amateur (as well as several other prior times on Cloudynights):

. . . . . . . APPROXIMATE CRATER DIAMETERS . . . . . . .
. . . . . . . . . . (+/- 0.2 miles uncertainty) . . . . . . . . . .

. . . The "BIG FOUR" (+1) . . .
A = 1.6 miles (2.6 km) B = 1.3 miles (2.1 km) C = 1.4 miles (2.3 km)
D = 1.2 miles (2.1 km) W (on west-northwest wall) = 1.9 miles (3.1 km)
NOTES: Although many amateurs rarely seem to see very much on the apparently smooth dark floor of Plato, the above craterlets are the ones most often reported by those lucky enough to get really good seeing. "A" is the easiest of this group due to its fairly prominent ramparts, and has been reported in a 4 to 5 inch aperture, although the unresolved "bump" of craterlet-A's ramparts is visible in only a 3.1 inch. 3 or 4 of these craterlets can sometimes be observed under low sun angle and in good to excellent seeing in apertures 6 inches and *larger*. These four can sometimes be "detected" as very tiny white spots in 3 to 5 inch scopes during the full moon, although to show them all as true pits often requires a 7 or 8 inch aperture. The "East Wall Pit" is a much larger irregular feature (4 miles across) which often hides in the shadow of the eastern wall during the lunar mornings. It may not be an impact crater, but more of a slumping of a segment of Plato's wall. There is also a small but prominent craterlet "W" low on the west-northwest wall north of the west-rim bow-in which is about 2 miles across. It is somewhat more difficult to observe than its size would indicate, mainly due to wall-shadow concerns and the crater's tilt.

. . . The "Little Four" . . .
e = 1.1 miles (1.8 km) f = 0.9 miles (1.6 km) g = 0.9 miles (1.3 km) h = 1.4 x 0.9 miles (2.2 x 1.4 km)
NOTES: Craterlet-e has been sighted in a good 8 inch, but craterlet-f may take a bit larger scope to see with any regularity. "e" tends to hide in the long early morning shadows, as "f" does also in the low lunar evening. The Lunar Orbiter shots of Plato show that "h" is a tiny double craterlet with 0.9 and 0.8 mile diameter components, forming an elongated 1.4 x 0.8 mile feature visible in larger apertures, but not fully resolved. Again, very high lunar sun may allow some of these cratelets to be "detected" as tiny white spots near full moon. The "Big Four", and the "Little Four" probably represent most of the craterlets on the floor of Plato which might be visible to amateurs using moderate to large apertures under excellent seeing.

. . . The "Tiny Ten" . . .
i = 0.8 miles (1.3 km) j = 0.8 miles (1.3 km) k = 0.8 miles (1.3 km) l = 0.7 miles (1.2 km)
m = 0.7 miles (1.2 km) n = 0.7 miles (1.2 km) o = 0.8 miles (1.3 km, double craterlet)
p = 1.0 x 0.6 miles (1.6 km x 1.0 km, triple craterlet) q = 0.9 x 0.6 miles (1.4 km x 1.0 km, double overlapping crater)
r = 0.8 miles (1.3 km)

NOTES: These are extremely difficult to observe as anything other than tiny white spots or rimless pits, although i, j, m, and o2 have been imaged by Maurizio Di Scuillo using a CCD camera on a ten inch Newtonian optimized for high resolution planetary work. Craterlet k has a very small pit to its west and will be tough to resolve easily. Craterlet m is a fairly shallow bowl with little in the way of a rim, so it is more difficult than its size would indicate. "n" is a very small rimless pit just to the east of a tiny white spot which is often mistaken for a crater (may be a small mound or ejecta blanket). Craterlet o is a double craterlet, which forms a 1.2 mile x 0.6 mile elongated feature. p is a triple, consisting of 0.7 mile, 0.6 mile, and 0.3 mile craterlets in close proximity, which might be detectable in very large apertures as a single almost rimless 1.4 mile x 0.6 mile feature (not resolved). Craterlet q is two very small overlapping craterlets which form a single 1.2 mile x 0.5 mile feature. r is right on the edge of the north-eastern floor of Plato and is hard to see due to shadowing. Lunar Orbiter images show a large number of smaller pits down to 0.25 miles across on the floor of Plato, but the above three "families" are probably the only ones which have much of a chance of being seen visually from Earth.

Below is the "rectified" Lunar Orbiter image that was used for the initial measurements (courtesy NASA):

Clear skies to you.


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6305392 - 01/11/14 01:57 AM

Yea, I see where're you going. Osiris is a great example, actually. It's a white speck in much the same way white specks are on the moon and probably for the same reason. So, yes, at less than true resolution of light and about 5% grey space we see specks smaller than the resolution of our aperture when seeing allows it.

Ideally, I would assert, you could see a point source "speck" at 1/4 Raleigh limit and even smaller if it were bright enough (enough contrast at maximum spacial frequency.) You could see something as small and bright as the apparent angular diameter and magnitude of Sirius if such an object existed on the moon. Or maybe if such a small feature existed and was properly illuminated on the dark side of the terminator. It would have more contrast there. I wonder how many of those "city lights" are very small features just over the terminator? Lit crater rims certainly appear brighter, yea?

I may be off my rocker on this being theory, its likely more difficult in practice in average to good seeing. But, I assert, it's always about contrast and not about angular diameter, though some angular diameter near Dawes at a minimum is required for craterfrom resolution. Specks have no such limit and can be seen as small as you like, provided they are bright enough relative to the lunar surface.

Using the small angle formula, I get Dawes to be closer to 1 mile in diameter than 1.5 miles at the moon's average distance, where angular measure in arc seconds = 206265 * diameter/Distance. So, a crater 1 mile across at 238,855 miles distance would be about 0.86" arc. That's comfortably above Dawes (and even a bit more than Raleigh for a 30% obstructed 150mm aperture calculated using a factor of 1 -co^2 ~ 0.91 * Raleigh limit.) Of course, that is the diffraction limit and seeing must allow it, otherwise it becomes an observation "in practice."

In theory, solving for diameter in the equation above and assuming theta to be 0.77" arc (Dawes for 6" aperture) we should be able to see crater's down the about 0.9 miles in diameter provided contrast remains above 5% due to surface albedo, seeing, aberrations, obstructions, and everything else that reduces contrast on those scales. Actually, Dawes should be somewhat less in an obstructed scope. In theory, nearer to 0.7" arc for a 30% 150mm aperture using the same 1 - co^2 factor as an approximation near maximum spacial frequency. So, that should reduce the theoretical diameter of a lunar crater to about 0.8 miles. Now, in practice with aberrations, seeing, and loss of contrast in a less than perfect obstructed optic that figure is probably closer to 1 mile when it's all said and done...in practice.

That means any craterlet about 1.6km, such as g or h, /might/ be in crater form when conditions are perfect for a 150mm aperture. But, this may be where Plato's darker floor comes into play lowering the contrast against what remains of the shadow's ~5% contrast transfer on the focal plane - makes those two extremely difficult if not impossible and slightly larger craters tough but not impossible. For larger craterlets, seeing disrupts them more often than not.



Edited by Asbytec (01/11/14 02:21 AM)


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Asbytec
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Re: Plato's challenge new [Re: David Knisely]
      #6305411 - 01/11/14 02:23 AM

Dave, I'm sure I got both from you years ago (but cannot find the thread to link the source.) It's a great piece. Mulling over your thoughts. I've read them before, but need a refresher. Thanks.

Initially, if crater diameters are (understandably) off by +/- 0.2 miles, that changes which ones can be resolved a bit. But, I did nail E one in 150mm, nothing smaller on Plato, yet. So, at least that one is doable and above the resolution limit for that aperture as a minimum.

I am not sure what is meant by optimizing for high resolution lunar and planetary imaging. Often that means a smaller CO and better contrast on scales out to the first ring or so. Really what's needed is to push high resolution into that tiny realm where obstructed scopes out perform perfect unobstructed ones on smaller scales near the spurious disc. That normally means a larger CO on the order of 40% to maximize that high frequency range. And it means everything needs to be diffraction limited, including seeing and aberrations...the aperture needs to be the limiting factor. Again, that's in theory and a benchmark to shoot for.

In practice, I think Plato's floor contrast ups the ante on these tiny ones. All we see is a speck in modest apertures because the floor washes out the already very low contrast of the craterlet's pit and the rim or wall should be brightly lit, as well, to see it in speck form. They do need more aperture in practice for crater form resolution and in this special case of Plato. Out on the brighter open plain, the story changes in favor of higher resolution pushing closer to theoretical resolution of a perfect optic as possible. This is where I could push closer to 1 mile resolution, and haven't done so on Plato yet.

That's the essence of this Plato challenge, right? To see where this proverbial contrast wall stops us in various apertures? How small can we go in crater from resolution is a function of how much contrast (seeing, aperture, obstruction, aberration, etc.) is available. Otherwise, we see a speck if anything at all.

Edited by Asbytec (01/11/14 03:09 AM)


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David Knisely
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Re: Plato's challenge new [Re: Asbytec]
      #6305502 - 01/11/14 05:26 AM

Asbytec wrote:

Quote:

Initially, if crater diameters are (understandably) off by +/- 0.2 miles, that changes which ones can be resolved a bit. But, I did nail E one in 150mm, nothing smaller on Plato, yet. So, at least that one is doable and above the resolution limit for that aperture as a minimum.




The lunar distance varies by about 5.5 percent from its mean value, so you can expect up to an 11% variation in the resolution. The old "9/D" (D is the aperture in inches) for craterlet diameter (in miles) approximation is just that, so craterlet e might just be possible in a 150mm aperture scope depending on the conditions. I have only managed it in 8 inch and larger apertures, but you never know.

Quote:

I am not sure what is meant by optimizing for high resolution lunar and planetary imaging.




In Maurizio's case, it means a 10 inch f/8 Newtonian with a very very smooth and well-figured set of optics and a small secondary mirror. With a lot of image processing, some of his shots showed more than 20 cratelets on the floor of Plato, which is more than I usually see in my own 10 inch. With my 14 inch, I could see a lot more (I have gone down to around a kilometer or so), but seeing has to be unbelievably good. Clear skies to you.


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Asbytec
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Re: Plato's challenge new [Re: David Knisely]
      #6305639 - 01/11/14 08:27 AM Attachment (29 downloads)

David, yes, the lunar distance is critical to determining the actual diameters using an aperture's resolution as a guide. Apparent diameters change with distance, for sure, and there is always room for error.

Image processing enhances contrast not readily available to the eye-brain visual image, so that an image captures more is not surprising. But, what can the eye-brain do is the interesting question. I think it starts with Dawes, which is an empirical visual observation made with a real aberrant aperture and in real seeing conditions, then work backwards a bit to find a limit for a given aperture.

Plato will require a little more from us, but how much? That's what makes the challenge interesting. We get to push man and machine to the limits and begin to define those limits. It's a fascinating topic.

I forgot about W, that makes 6 in crater form (attached.)

-------------------Optional and possibly confusing reading below

Dawes, or actually Lambda/D as an approximation of Dawes, is about 113.4/Dmm. It changes a little with the magnitude of the point source, but we can assume the moon to be mostly bright (crater rims) and any diffraction affects having relatively stable and modest magnitude. Dawes also applies to 100% object contrast between two points in black space and ends with 5% image contrast. The moon is very high contrast, but I doubt its 100%. The lit rims are pretty bright, but the pits may not be completely black and devoid of light so the range between the two is likely a bit less than 100%. So, already it looks like reaching Dawes is very difficult visually.

Dawes for an aberrant 6" obstructed aperture would be 113.4/150mm * (1 – co^2) ~ 0.69" arc. At the moon's mean distance and approximating with the small angle formula we arrive at ~0.8 miles in diameter - at that mean distance. In my experience not having resolved to Dawes (as expected), but getting down to about 1 mile (not in Plato) equates to about 0.86" arc resolution. So, I am sure that level of resolution is possible in diffraction limited seeing. That turns out to be slightly better than 0.92" arc for Raleigh limit (calculated normally with 138.4/Dmm, but observed with an obstructed aperture with a modified Raleigh limit of 0.83” arc.) It's not quite as good as modified Raleigh (caused by to obstruction diffraction effects), however. So, an unobstructed and unobstructed, aberrant aperture should resolve craters at least to about 1.04 * Raleigh limit. (The extreme precision is exaggerated to show how close to modified Raleigh 0.86” arc actually is.)

However, that may not be the best than can be done visually; it's only my own best. That's about 1R for all reasonably good apertures in diffraction limited seeing, IME and IMO. And that makes some sense being that Dawes leaves 5% contrast on the focal plane and Raleigh about 28% (which appears as a black space.) The moon might not be quite 100% starting contrast, so in theory it should not provide 5% on the focal plane at Dawes. But, it should not begin with nor loose, through contrast transfer, so much that Raleigh separation falls from 28% to less than 5% on the focal plane, either. So, it makes sense to me, and seems consistent, any resolution limits should be reached at less than Raleigh (138.4/Dmm) but larger than Dawes for obstructed apertures and right at Raleigh for unobstructed apertures. This is, after all, the domain where obstructed scopes rule.

That "E" being approximately 1.2 miles in diameter set on a darker floor was seen in crater from with a 150mm aperture (assuming mean distance and a diameter close to shown) suggests the same approximation for resolution to lie slightly larger than the Raleigh limit at 1.03” arc, as expected. That 1.2 miles (approx) is closer to 7/D. However, the modified Raleigh limit is closer to 0.83” arc, so the loss is somewhat more significant. This is about 1.2 * the modified Raleigh limit for an obstructed aperture. Applying the same figure to a clear 150mm aperture we might arrive at a resolution of 138.4 * 1.2 = 166/Dmm for Plato craterlets, at least or about 1.3 miles in diameter. Maybe better, but that’s about 8/D.

Such is the effect Plato’s contrast has on resolution; we lose the Raleigh limit by a factor of about 1.2, it seems.

Again, applying the small angle formula using the moon's mean distance we arrive at 1" arc resolution for one Plato craterlet (“E” at 1.2miles approximately) on that night, at least. This is slightly above the Raleigh limit for a 150mm aperture and is expected because beginning object contrast on Plato is reduced. So, since contrast and spacial frequency are inextricably bound, we'd expect the diameter to be a bit larger to leave sufficient object contrast transferred to the focal plane.

Thus, the diameter of crater's that can be seen is not so much a function of diameter, but of object contrast. And on Plato, they have to be a bit larger than normal or require slightly larger aperture.

The math above is an approximation based on my own experience with craterlets against the moons brighter surface and on Plato. It does not define anything, it just gives a range - between conventional Dawes and Raleigh for unobstructed apertures - I think one can expect to observe when the air is diffraction limited. Actually, 9/D is a good approximation for average conditions, but I think it might be a bit pessimistic for excellent conditions which can push toward 7/D. And that's fine, they are only approximations given so many variables exist such as actual distance, diameters, and conditions. On most nights I cannot see "E", and often enough even A through D can be tough. But when seeing is diffraction limited, all 6 can be seen when the lighting is right.

Edited by Asbytec (01/11/14 08:51 AM)


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6305690 - 01/11/14 08:57 AM

Dawes for an aberrant 6" obstructed aperture would be 113.4/150mm * (1 – co^2) ~ 0.69" arc.


Norme,

I thought .76 arc sec was Dawes for a 150mm.


Pete

Edited by azure1961p (01/11/14 08:58 AM)


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6305712 - 01/11/14 09:13 AM

It is, but added diffraction due to an obstruction changes that by a factor of 1-co^2 approximately and for coherent light. So, it is somewhat less than 116/Dmm (or 113/Dmm for Lambda/D criteria for resolution approximating Dawes) depending on the size of the obstruction an with somewhat incoherent light. It might be about 105/Dmm ~ 0.7" arc for a perfect 150mm aperture and somewhat more for a real one. Remember, at this very high spacial frequency is where obstructed apertures /can/ rule and /can/ exceed perfect unobstructed performance given a reasonably good Strehl. This extended spacial frequency can improve high resolution provided the atmosphere is not working against it. So, yes, officially Dawes is 0.76" arc for a 150mm, but it should be a bit less when that aperture is obstructed.

Edited by Asbytec (01/11/14 09:24 AM)


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6305970 - 01/11/14 11:16 AM

Norme in your last photo there is a crater near the rim of Plato at the two o'clock position. That is one that I'm certain I detected last winter and wonder why it's not labeled? I remember that one as being resolved along with 6 others, and crater h was the albedo feature I noted.

A star is a point source of light. If my optic catches enough light from that point source it will form an image my eye can see. Any spot of the lunar surface, like the rim of a craterlet, can act as a point source of light that my optic/eye can detect even though my optic isn't capable of resolving that feature. If I used a photosensitive device and digital image processing, I might be able to discern several point sources of light in a curved line that would indicate the structure, even though my eye couldn't. Those multiple points would have to be separable by my optic of course otherwise they'd appear as one spot.

There is the theory and practice of telescopes on earth being separated by distances so that the total resolution becomes something of the order of the separation distance. I wonder if there are any amateurs engaged in that? Or is it really only practical for radio devices


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6306050 - 01/11/14 11:52 AM

That looks like "f" as labeled in David's graphic at about a mile in diameter. That's a great catch. In your 10" scope? Do you remember what your seeing conditions were or the moon's distance that night?

So, h was a albedo "speck?" That one would be curious to know how it resolves out - as one elongated object (crater or speck) or two distinct features. I cannot remember which specks I saw, would have to dig way back into the CN archives. I don't remember seeing a double speck, anywhere.

Quote:

Any spot of the lunar surface, like the rim of a craterlet, can act as a point source of light that my optic/eye can detect even though my optic isn't capable of resolving that feature.



Absolutely. I guess that's why we see specks, instead. Normally the smallest craters do not form specks in my scope, they have to be something larger than a point source (being defined as 1/4 Airy disc diameter, or about 0.4" arc. That's pretty small, less than 0.4 miles.) Otherwise Plato should be covered with specks and maybe all of the labeled one in David's graphic, at least.

So, it seems we have crater form to some level of resolution (I'm curious about), bright specks below that (kind of curious about that, too), then we see nothing further down the resolution chain. But, we would if they were bright enough. Most are not. But you know...specks might be a bit easier (and crater from more difficult) on Plato because it is a tad dark.

Anyway, I hope you guys can report sightings, if seeing ever allows good look at Plato I'll join in. Resolution is an interesting topic and Plato is an interesting place to try to understand it and the limits of our equipment and conditions. It gives us a feel for what we can expect to see. Maybe we see more specks per capita on Plato than elsewhere?

It would be very interesting to note the affects of seeing in larger apertures, too. They might be hard pressed to reach the diffraction limit, but they are still supposed to resolve quite nicely since their diffraction limit is much smaller, anyway. So, even if they are not at diffraction limited, they are returning smaller discs (short exposure FWHM) even in less than perfect seeing. That's the theory, does it hold? I'd think so.

Edited by Asbytec (01/11/14 11:56 AM)


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Asbytec
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Re: Plato's challenge new [Re: Asbytec]
      #6306149 - 01/11/14 12:44 PM

Quote:

Those multiple points would have to be separable by my optic of course otherwise they'd appear as one spot.




This whole idea and the mechanics behind our ability to probe the world beyond fascinates me to no end. I like to really push it for everything it's worth in the real world and try to understand it in theory. Often the two are not far apart. It's just a step we take to delving into our hobby, not unlike a surfer waxing his board and reading the waves for the best break.

I had to come back to your idea of the expanding point source. At some point larger than about 1/2 Raleigh, the visible disc expands noticeably to the eye. This may well be the curve of a crater rim as much as it would be a Jovian moon. So, at some intermediate point between point source and full blown expanded object, we see an expansion of the spurious disc. I wonder how many specks we observe on Plato are actually expanded in this way at least somewhat. Are they indeed expanded perpendicular to the sun's angle? Is the floor visible at this point, or is this the range of angular dimension that defines a speck without a visible floor? Not a perfectly round speck like a spurious disc, but an elongated one defining a crater rim as a speck to our eye?

That needs a closer look. If so, then a speck might well be resolution of a crater rim even if the floor is too dim to see. Or it could be the two are not mutually exclusive, once you see the rim you see the floor and a speck is still a speck.

Edited by Asbytec (01/11/14 12:52 PM)


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David Knisely
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Re: Plato's challenge new [Re: Asbytec]
      #6306272 - 01/11/14 02:06 PM

Asbytec wrote:

Quote:

Dawes, or actually Lambda/D as an approximation of Dawes, is about 113.4/Dmm. It changes a little with the magnitude of the point source, but we can assume the moon to be mostly bright (crater rims) and any diffraction affects having relatively stable and modest magnitude.




Dawes limit is *only* applicable as an approximate limit for a pair of equal point sources, not for an object that contains extended detail. A craterlet on the moon is an extended object, and point-source limits cannot apply to them. For that, you have to use a limit that is somewhat larger than Dawes. The British observer Wilkins in 1959 did a detailed set of measurements in various apertures and came up with the approximate relationship that a craterlet half-filled with shadow would be visible on average if it had a diameter (in miles) equal to 9/D, where D is the aperture of the telescope in inches. It is again an approximation, but it is somewhat useful, as in a 150mm aperture (5.9 inch), it predicts a minimum size of about 1.5 miles for t he smallest craterlet visible. I have done some work with high-resolution charts and found this guideline to be fairly accurate. Its predictions are much more realistic than a figure derived from Dawes limit. Smaller linear features such as rilles or tiny mounds can be detected in a given aperture at notably smaller sizes than craterlets due to their simpler diffraction structure, but seeing craterlets as the true pits they are requires a somewhat larger telescope. Clear skies to you.


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6306791 - 01/11/14 06:24 PM

You're going deep Norme. Are you angling for a job at JPL

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azure1961p
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Re: Plato's challenge new [Re: nirvanix]
      #6307181 - 01/11/14 10:33 PM

The only caveat in assigning or guesstimating point source contrast on the moon is it would need to be high contrast indeed. A mountain peak at say a quarter mile across seen from the depths of the night side of the terminator could produce such a stellar-like diffraction pattern - though of much less intensity, ie; the .25 mile mountain peak would not be bright enough to illuminate diffraction rings in the said instrument. Of course Im guessing here as I haven't find such a thing but stellar point sources say, in the 1st magnitude certainly are far far higher a surface brightness per unit area producing the pattern. If our telescopic views had planetary bodies with this kind if brilliance wed have a battery of done extremely dark neutral density filters.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6307192 - 01/11/14 10:36 PM

- that all said, if I were looking for detail other than rilles significantly below Rayleigh for example, Id imagine the starry lone peaks emerging from night might be the ticket to some extraudinary examples.

The problem is in measuring off the glint of light creating the sub angular res.

Pete


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Re: Plato's challenge new [Re: nirvanix]
      #6307283 - 01/11/14 11:23 PM

David, observing E seems to best 9/D by a factor of ~ 0.8. I am looking for a reason why that would be. Yes, Dawes technically applies to two moderately bright point sources with 100% object contrast. As a starting point, I agree Dawes is too optimistic for an extended object and actually find Raleigh a bit more achievable (in the thought process and experience above.) Dawes requires 100% object contrast to retain enough after transferring the object into an image on the focal plane.

Raleigh leaves enough contrast from lunar features to be seen, I suppose, and it might be bested when conditions are favorable. Having observed craters down to about 1 mile in diameter away from Plato strongly suggests Raleigh to be a better resolution criteria, even though it also applies to two moderately bright stars set in the blackness of space.

From the data on craterlet E, it should subtend an angular diameter of 1 to 1.1" arc between perigee and apogee. Raleigh is, of course, 0.92" arc so this one just does not quite resolve down to Raleigh if it is a limiting crater with a diameter of 1.2 miles.

If it is, and it can be seen in a 5.9" scope, then that level of resolution is 7/D and even 8/D if "E" is larger in diameter by +0.2 miles. And this makes sense because the object starting contrast is somewhat reduced, which is the essence of the Plato challenge. If E is between 0.98 to 1.1" arc, then it's diameter can range from 1.1 to 1.3 miles in diameter at mean distance which implies resolution from 6.5/D to 7.5/D.

Again, E was only spotted once in a period of excellent seeing, given the opportunity and as infrequently as I view Plato. But, I think it's telling in terms of what can be done. And again, because there are so many variables involved in resolving a crater, and approximation is very difficult to apply across the board to all observers on average nights. It seems 9/D is a reasonable assumption for average to good conditions covering most nights and most observers who observe on those nights. It accurately describes what I see most of the time.

Being able to go deeper really speaks to how important diffraction limited seeing is to everything we do and when we're lucky enough to have such skies. In those instances, and in real terms of what an aperture /can/ do, I suspect something less toward 7/D is possible as a limiting observation...if nothing smaller can be seen in a 5.9" aperture (on Plato) and if E is about 1.2 +/- 0.1 miles in diameter.

So, that's my challenge to Plato observers, to see what shows up in those best moments when seeing is diffraction limited if it get's there. I got 6 in crater form, Nirv got 7. I doubt I can get more having reached what might be a limiting observation, but I bet larger apertures can until they bump into constantly less than diffraction limited seeing with increasing aperture. From that point, resolution begins to deviate from diffraction limited but larger aperture should still best a smaller one unless seeing is very bad.

A good amount of magnification is required, too, to really inspect that realm of the very tiny. The diffraction discs can be seen at 1mm exit pupil, but I suspect they are too bright causing some physiological eye response. Magnification near 0.5mm exit pupil should dim the moon sufficiently without reducing available contrast on the focal plane. I saw E at 0.47mm exit pupil (320x.) The moon is not so dim where the eye's response looses photopic vision.

I find smaller detail is more easily noticed at smaller exit pupils, of course without any increase in resolution in that realm. They are just bigger and dimmer. The point being, maybe it's not good to use 1mm exit pupil in some cases, especially when the object is very bright. You may not notice a tiny feature or loose it in the glare, maybe missing the crater floor near a bright rim when the image is small and bright.

Nirv, hey, it was your comment that drove me to lay awake in bed crunching numbers and concepts when I should have been sound asleep. Job? Na, this is pure interest and enjoyment. That's what drives such long winded posts full of theory, speculation, experiences, and a mix of all the above. This isn't work, is it?.


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Re: Plato's challenge new [Re: Asbytec]
      #6307342 - 01/11/14 11:56 PM

BTW- the reason Norme, that you don't see Plato covered in extraordinarily small craterlets as veritable point sources is that very often these small features have very smoothed *walls* often with no discernible rim. As a result transitioning from plain to crater pit is more gradual and as a result contrast on these very small features is softened still. Apollo 12s site for example is covered in these eroded craterlets, smoothed over time.

I think in theory point source craters exist on the moon and in reality too, but the corridor that would present such a view is narrow and conditional.
You need an isolated point of brilliance - again - against the backdrop of the shadowed terminator/night side.

Pete


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6307358 - 01/12/14 12:16 AM

Quote:

...often with no discernible rim...as a result contrast on these very small features is softened still.

You need an isolated point of brilliance - again - against the backdrop of the shadowed terminator/night side.




Makes sense, Pete, that seeing a speck is a matter of illumination and contrast. As the sun angle rises on even a small rimless crater, it illuminates the far wall. As that source of illumination grows, maybe it will have enough illumination from the rim/wall to be visible as a speck if it's lit surface area reflects enough light against the lower grazing angles of the general lunar surface. That seems to put a lower bound on the diameter one can see as a speck, just speck-ulating.

But, I can't escape the hypothesis that specks form when the crater wall or rim is large enough to reflect enough light (along with any inherent albedo.) And if they are that large relative to aperture, are they large enough to be seen as extended? That will require some careful observation of tiny specks to detect any elongation and with a preconceived notion of what they might look like. Very difficult at best.

But what about specks at higher sun angles? Do we see fewer or more of them? Does the crater need to be much larger at those sun angles? And does Plato's dark floor help bring them out?

We've seen elongated specks over the terminator, sometimes I even focus on and evaluate seeing with them. Thinking about it, though, at those sun angles those features are most likely higher peaks. Yea?


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Re: Plato's challenge new [Re: Asbytec]
      #6307789 - 01/12/14 10:12 AM

Not all albedo spots are craterlets. We can be fooled into thinking a spot we see on the lunar surface is a craterlet, when it is not. And many times when a craterlet is at high sun angles, it will be difficult or impossible to see the craterlet as anything but an albedo spot. Depending on aperture, some craterlets can never be seen except as albedo spots.

IME & IMO, the best course is to consult high resolution lunar photos when in doubt about whether an albedo spot is a craterlet or not.

Mike


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Re: Plato's challenge new [Re: Asbytec]
      #6307825 - 01/12/14 10:33 AM

Quote:

But what about specks at higher sun angles? Do we see fewer or more of them? Does the crater need to be much larger at those sun angles? And does Plato's dark floor help bring them out?




I see more albedo spots most everywhere on the Moon at higher sun angles. To my eyes, Full Moon reveals more albedo spots at one time than any other phase. The contrast between spot material and surrounding regolith will determine if we see an albedo spot or not. Some albedo spots will be craters that we cannot resolve. Others will be domes. Still others will be unusual contrasts between a local area and the surrounding area, for whatever reason, such as Reiner Gamma.

Quote:

We've seen elongated specks over the terminator, sometimes I even focus on and evaluate seeing with them. Thinking about it, though, at those sun angles those features are most likely higher peaks. Yea?




I've seen these terminator specks many times. To me, they are some of the most enjoyable lunar phenomena to observe. The specks can be most anything that is more highly elevated than the surrounding area. They can be mountain peaks, crater rims, domes, dorsa, even rupes and rimae, I suppose.

Mike


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azure1961p
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Re: Plato's challenge new [Re: Sarkikos]
      #6309018 - 01/12/14 08:18 PM

Full moon is an excellent lab of sorts to study composition independent of light/shadow intrusions. A true full moon I dislike though - even a sliver of some terminator 20 miles side is appreciated Mike. We are fortunate much as I think its taken for granted that we can see the high angle lit moon.

Norme,

The thing - alluded to with smoothed craterlets- is that while Rayleigh makes a nice realistic measure for craterlet limit res - its more difficult in arriving at such a thing due to the variance in crater age/erosion. Interestingly, the aged smoothed craters are almost analogous to Dawes with progressively fainter stars beyond 6V until after around 10V (with a medium aperture) Dawes almost doesn't apply at all. So too with craterlets - fresh, nicely chiseled crater walls on a 6.5 or 7/D craterlet and all as should be. But add some parameters beyond that - bright ejecta blanket or eroded shape - and we've exceeded the ?/D parameters.

This isn't to steer away from arriving at such a measure or limit, but to realize like Dawes, there are qualifiers needed in contemplating what candidate craterlets make the cut. The excellent thing here is that these candidates need not lurk in some mist of unverifiable neverland. We've got astonishing images of the entire moon that go beyond the level of resolution needed to sort things out.

Think - Im going to have a look see myself...

Pete


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Re: Plato's challenge new [Re: Sarkikos]
      #6309178 - 01/12/14 09:54 PM

Mike, we might see more albedo features at higher sun angles. That seems intuitive and might agree with my own experience. Or at least my own perception. But what would be the mechanism that makes a crater look like a bright spot instead of disappearing into the high sun lit surface?

It's walls are still angled a bit, that doesn't change with sun angle, of course. But, what does change is the reflected radiation from the 'flat' surface. And if that surface is bright, the crater might still be a bit brighter but the difference (contrast) between the crater and the bright surface would diminish markedly. That would suggest we might see less specks per unit area.

It's also likely true that crater features seen at lower sun angles, they may become more bright speck like features instead. This would increase the total number of specks we see as larger craters transition from crater form to speck, but any specks we see at lower sun angles might disappear in the process. So, we may see more specks, but they may not be the same specks.

I am just speck-ulating here as I am not sure I understand the phenomenon of speck formation. Is it an unresolved crater or dome of any other small reflective feature? Or can resolved craters at a range of diameters become large bright specks without a floor at higher sun angles? So, does this increase the number of specks seen, or do we somehow loose these smaller ones at higher sun angles? I don't know, but surely Plato's darker floor would help preserve bright specks seen. (As a Hypothesis...)

So, if a speck can be any feature, how can we call it resolved as a crater without double checking a chart. In other words, when observing Plato and you note some specks, how can you call one of them 'j', for example. It would be interesting to see how many specks can be seen at lower sun angles and at higher ones. And which craters those would be - if we lost the smaller ones and the larger ones became specks. And why do they become specks, does the angle of their walls reflect more light toward us like a giant mirror?

Just thoughts...


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Asbytec
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Re: Plato's challenge new [Re: Asbytec]
      #6309242 - 01/12/14 10:23 PM

Pete, the thing that still keep haunting me is Raleigh for a 6" is 0.92" arc as calculated using 138.4/Dmm. Using the small angle formula, that translates into a crater 1.1 mile in diameter at the moon's mean distance of 238,855 miles. With CO effects, you /might/ get smaller down to 1 mile if seeing is absolutely lab-like at 8/10 Pickering or better and everything else is working in your favor.

As far as I know, I've gotten down to 1 mile (+/-) given errors in measurement. So, let's say 1.1 mile in diameter is doable in a 6" aperture at Raleigh at the moon's mean distance in excellent seeing, cooled, well collimated, and all that. That's already pushing 1.1 mile ~ 6.6/D for the Raleigh limit. On Plato, I know "e" can be seen in a 5.9" aperture when conditions are nearly perfect. If it is 1.2 miles in diameter, that is 5.9 * 1.2 ~ 7.1/D. In measurements from this site, "e" is actually on the small side toward 1 mile or about 1.7Km, or closer to 1.1 miles in diameter.

But, the figure given by 7/D ~ 1.2 miles is only 0.3 miles short of the figure for 9/D ~ 1.5 miles. So, we're in the ball park where seeing could account for any difference easily. So, on Plato, 1.1 miles in diameter is not quite as good as Raleigh, especially if Raleigh for an obstructed scope should show craters down to 1 mile. That seems to rule out Dawes as a limit as does the remaining contrast transferred from such a small feature.

Sorry, in a hurry...back later. But, yes, these are basic assumptions with so much at play...probably all dealing with object and image contrast.


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Sarkikos
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Re: Plato's challenge new [Re: Asbytec]
      #6309310 - 01/12/14 10:53 PM

Quote:

Mike, we might see more albedo features at higher sun angles. That seems intuitive and might agree with my own experience. Or at least my own perception. But what would be the mechanism that makes a crater look like a bright spot instead of disappearing into the high sun lit surface?




I think we must go back to how the crater originated. When the meteorite hit the surface of the Moon, it may have brought up underlying material that has an albedo different from the surrounding regolith. Or volcanic outflow around the crater may have resulted in a difference in albedo. In any case, it is the contrast between the crater region and the surrounding area which produces the appearance of a bright spot.

And since the sunlight is concentrated into a smaller area of incidence at high sun angles, it seems reasonable to me that the contrast between the albedo spot and its environs would be more obvious at that time.

A different mechanism is working along the terminator to make some areas stand out. Then some areas are literally "standing out" to catch the sun rays, while adjacent areas are in shadow. There is the stark contrast between sunlit features and those in darkness, rather than a difference in albedo emphasized by the intense light of high sun.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6309487 - 01/13/14 02:03 AM

Mike, you're right that craters disturb the dust and have some brighter albedo. At least some do, younger ones, or whatever. Your point is made and it does have an affect. And since it is lighter, it should be brighter. I guess my question is, as the sun rises and the surrounding terrain is more brightly lit by the direct suns rays, if that bright crater falls off in contrast relative to it's brighter surroundings. Maybe to the point it can no longer be "resolved" as a speck in a given aperture. Surely some do, especially smaller ones relative to the resolution of that aperture. This behavior, if it happens, would be interesting to note inside Plato over time...rather than just counting them on a given night.

Possibly some larger craters evolve from crater form at low sun angles into bright spots (larger than pinpoint specks, if specks are pin points) as the sun angle increases probably due to the same albedo material. They are large enough to reflect a lot of light. Maybe being resolvable, they even provide a brightly lit surface area on the retina. If memory serves, A through D - the big 4 - inside Plato, become more like bright spots as the sun rises higher. I am wondering how many of the smaller craterlets can still be seen as specks during Plato's high noon. All of them to some almost resolvable diameter and what diameter would they be? Are there more of the tiny ones, or less of them? And how does that contrast (pun intended) behave with the generally brighter lunar albedo outside Plato?

I dunno, maybe specks do brighten as the shift form being rim lit on less brilliant surface to being fully lit on a brighter surface - effectively neither appearing or disappearing with sun angle. There is just more of them as the larger craters pit's become fully lit, too.

Edited by Asbytec (01/13/14 02:20 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6309504 - 01/13/14 02:35 AM

Pete, you know what else I was thinking? I probably do more double star work that small lunar crater spotting. Maybe because doubles are easier. What I mean is, we can split a Raleigh double fairly easily and quite readily almost regardless of the seeing. But to resolve a crater at that same level of resolution requires an exceptional night. When I first got my scope, I was hunting the smallest craters I could possibly see. It took some effort and very steady moments. A Raleigh double is not nearly as taxing, nor is a Dawes split for that matter. Surely that's a difference in object type and contrast involved.

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Re: Plato's challenge new [Re: Asbytec]
      #6309695 - 01/13/14 08:07 AM

Probably to do with craters appearing smaller than they are since they are dark or black rather and the surrounding contrast bleeds over into this area. Conversely doubles are bright and space is black so they can be resolved closer and easier than a veritable negative of the same spacing. What do you think?

Pete


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Re: Plato's challenge new [Re: Asbytec]
      #6309751 - 01/13/14 08:43 AM

Quote:

I probably do more double star work that small lunar crater spotting. Maybe because doubles are easier. What I mean is, we can split a Raleigh double fairly easily and quite readily almost regardless of the seeing. But to resolve a crater at that same level of resolution requires an exceptional night. When I first got my scope, I was hunting the smallest craters I could possibly see. It took some effort and very steady moments. A Raleigh double is not nearly as taxing, nor is a Dawes split for that matter. Surely that's a difference in object type and contrast involved.




I think this is because of the different types of object involved. Stars are pointicular objects, craters are extended.

When splitting doubles, you are dealing with the diffraction patterns of point sources, or with two overlapping diffraction patterns if they are a tight double. When observing craterlets, you are not at the same intense level of examining diffraction patterns as you are when viewing doubles. A craterlet involves a complex blending of many diffraction patterns, more like a continuum, something quite different than trying to split doubles.

I have heard that planet/lunar observation is more demanding than splitting doubles ... though maybe most doubles enthusiasts would never admit it. For top-tier planet/lunar observation, you need excellent seeing and excellent optics. For splitting doubles, you need only decent seeing and decent optics. As I said, I've only heard this. So far, I have much more experience with planet/lunar than with doubles.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6309849 - 01/13/14 09:36 AM Attachment (23 downloads)

Pete, yes, I think exactly that. The object contrast is a bit higher allowing us to resolve down to Dawes with 5% remaining. I suspect lunar contrast is not 100% meaning after contrast transfer we loose the 5% "required" by Dawes.

However, at Raleigh, the final contrast is much higher at 28% on doubles which appears black. For lunar, since beginning object contrast is not 100% like the black of space, it is also lower after being transferred by the optic. So, at Raleigh I suspect the crater floor "image" should be closer to grey as the crater floor "object" is probably not entirely black. And grey can be seen in the final image. Now, how about if Plato's floor lowers that object and image contrast even more...you need a bigger crater.

Curiously, Raleigh in a 6" subtends a crater about 1.1 miles in diameter at the lunar mean distance. Yet, I reported seeing one at 1 mile. How can that be? Perigee, maybe? Error in measurement? Surely some error. But, it turns out, due to the shrinking Airy disc problem, that is what an obstructed 150mm aperture should see as a limiting observation - right at 1 mile in diameter - at Raleigh.

Yes, they are complex extended objects. Mike, that lunar and planetary is more difficult is the realization that just dawned on me, so you heard it again. But, that's compared to equally bright close pairs, only, of course say at Raleigh or Dawes.

But, yea, it does seem a small crater to be seen needs seeing that makes 52 Ori look like a nice, clean pair of headlights. I think that's because they don't have that much contrast to loose before they become blurred beyond resolution. A bright equal double star's perfect object contrast can afford a little more loss in seeing and such before it is no longer resolved. That's my guess.

Playing around, and if you trust Aberrator. (I do, pretty much.) Notice how the floor of the 1" crater (slightly larger than Raleigh for a 6") is still grey? It gets darker with aperture and improved contrast transfer. Also, the 10" scope is just barely resolving the 0.5" crater. Maybe on a lighter background that dark speck would show better. Also, these images are processed with a slight bit of seeing and about 1/6th SA. They're approximation, surely, but that 1" arc crater looks a lot like "e" to my eye. (It needs to be smaller, though.)

Edited by Asbytec (01/13/14 09:56 AM)


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Sarkikos
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Re: Plato's challenge new [Re: Asbytec]
      #6309879 - 01/13/14 09:57 AM

I think the crux of the matter is that stars are pointicular objects, craterlets are extended objects, different animals entirely. There can only be limited extrapolation of experience and theory from doubles to craterlets. When we observe craterlets, we are not observing just two diffraction patterns as with double stars, but a complex continuum of many.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6310036 - 01/13/14 11:14 AM

Sorry if I wasn't clear, but oh yes, totally agreed. You don't even see diffraction discs unless the object is very small and very bright. Even then, it may itself be an extended object and simply look like an Airy pattern.

But, yea, the whole image is a composite of unseen and infinite numbers of diffraction patterns the brighter of which might be Raleigh's angular separation with dimmer ones between. You might be able to segregate those 'pairs' of infinite discs. (LOL) Or rather treat the image as a finite number of small spots no larger than 1/4th the Airy disc diameter, as an approximation. Yes, it's complex.

What would be your take on a resolution criteria and how might that apply to Plato? The best I've done is 1.2 miles (+/-) on "e." That makes sense to me in terms of Raleigh and object contrast and might even be a limiting observation.

Just grabbed a look at Plato under pretty thick thin clouds, if that makes any sense. The moon was in good seeing, but it was very grey. The sky, too. Quickly, just got 4 specks (the big 4.) That's it. Oh, and "W."


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Re: Plato's challenge new [Re: Asbytec]
      #6310366 - 01/13/14 02:04 PM

Quote:

You don't even see diffraction discs unless the object is very small and very bright. Even then, it may itself be an extended object and simply look like an Airy pattern.




The diffraction disk at high power is an extended object in the sense that it is "extended." But it is still only one diffraction pattern, not a continuum of them, as is the case with planet and lunar surfaces. This is a distinction with a difference and must have some optical consequences.

Mike


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Re: Plato's challenge new [Re: Asbytec]
      #6310384 - 01/13/14 02:12 PM

Quote:

What would be your take on a resolution criteria and how might that apply to Plato? The best I've done is 1.2 miles (+/-) on "e." That makes sense to me in terms of Raleigh and object contrast and might even be a limiting observation.




I've never counted craterlets in Plato, at least not in any systematic way. When I try for challenging lunar features, I usually go after domes or rilles.

The Plato Challenge is something I still need to do under good seeing and a favorable sun angle. The 10" Dob would be my best weapon for that battle. But the 6" SCT or Mak would be much more convenient ... if I can wait for them to cool-down. In my area they are better for summer work.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6311091 - 01/13/14 08:45 PM

Mike, sure, at some very high magnification the Airy disc does behave like an expanded object since it is not infinitely small in and of itself.

Yea, I hope you can do the Plato challenge. It was a challenge.

As they say, it gets worse before it gets better. I hope that applies to our weather. It's been not so goo and seems worse today. Maybe that disturbance will finally pass in a day or two. I may make nightly speck counts on Plato.


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Re: Plato's challenge new [Re: Asbytec]
      #6311207 - 01/13/14 09:46 PM

I missed it for this month , had a few days of clouds.

But I hear the moon a callin' I'll be back agin afore ye knows it


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Re: Plato's challenge new [Re: azure1961p]
      #6312475 - 01/14/14 02:56 PM

Quote:

Dawes for an aberrant 6" obstructed aperture would be 113.4/150mm * (1 – co^2) ~ 0.69" arc.


Norme,

I thought .76 arc sec was Dawes for a 150mm.


Pete




I'm afraid Dawes Limit is not defined for any particular telescope (obstructed or unobstructed). It is merely an empirical (and approximate) limit for the separation of equal double stars based on the observations of English astronomer William R. Dawes (1799-1868). It is not based on any optical physics so you can't just modify it in some way to account for a central obstruction the way that might be done with something like the Rayleigh criterion. Dawes Limit is just:

r = 4.56/D, where "r" is the double's separation in arc seconds and "D" is the aperture of the telescope in inches. For a 150mm (5.9 inch) aperture, Dawes limit would be 0.77 arc seconds. You can read the entire paper where Dawes first described his limit here:

http://articles.adsabs.harvard.edu/full/seri/MNRAS/0027//0000237.000.html

Dawes mentions his limit on page 237. Again, Dawes limit is not strictly applicable to extended objects like the moon and planets. Clear skies to you.


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Re: Plato's challenge new [Re: Asbytec]
      #6312609 - 01/14/14 03:46 PM Attachment (15 downloads)

Asbytec wrote:

Quote:

Playing around, and if you trust Aberrator. (I do, pretty much.) Notice how the floor of the 1" crater (slightly larger than Raleigh for a 6") is still grey? It gets darker with aperture and improved contrast transfer. Also, the 10" scope is just barely resolving the 0.5" crater. Maybe on a lighter background that dark speck would show better. Also, these images are processed with a slight bit of seeing and about 1/6th SA. They're approximation, surely, but that 1" arc crater looks a lot like "e" to my eye. (It needs to be smaller, though.)




You can't use Aberrator quite that way and expect to get results that truly depict what is achieved with the eye observing in an actual telescope. It just isn't highly accurate except for roughly demonstrating what aberrations do to an image. In fact, the creators of the software specifically say:

" The realitive effects from aperture and aberrations on such image will be realistic, but its not what you would encounter at the eyepiece."

Quote:

Curiously, Raleigh in a 6" subtends a crater about 1.1 miles in diameter at the lunar mean distance. Yet, I reported seeing one at 1 mile. How can that be? Perigee, maybe? Error in measurement? Surely some error. But, it turns out, due to the shrinking Airy disc problem, that is what an obstructed 150mm aperture should see as a limiting observation - right at 1 mile in diameter - at Raleigh.





Again point source resolution limits cannot be strictly applied to extended detail on the Moon and planets, so it isn't something to get terribly hung-up on. Just view the moon and record what you see as best you can (and be as certain as you can of exactly *what* you saw).

As for the central obstruction "shrinking" things, that isn't quite the whole story. One frequent statement by some authors is that a larger secondary can help increase the apparent resolving power of a telescope. This is somewhat of an exaggeration. While the diffraction caused by the secondary obstruction does cause a reduction in the diameter of the Airy disk of a star, the actual amount of reduction for common central obstruction sizes is slight, and would not help with detail in extended objects. It may slightly improve the ability of the telescope to resolve some close double stars but only when the obstruction reaches a somewhat large size. Indeed, the diffraction disk of a telescope with a 20 percent central obstruction is only about four percent smaller than that of an unobstructed instrument. Even a 33 percent central obstruction would only yield a 10 percent reduction in the Airy disk size, so for common central obstruction sizes, the "improvement" in effective resolution is minimal. The amount of energy put into the first ring by the obstruction would negate any alleged resolution increase on extended objects, reducing the contrast on high power planetary images and rendering small shallow craterlets near the resolution limit of the telescope more difficult to see. It is still better to keep the secondary obstruction under 25 percent if possible.

I went to the Lunar Reconnaissance Orbiter Camera site and used their PDS Archived Image Interface:

http://wms.lroc.asu.edu/lroc/

I used the scale they supplied at as high a resolution as I could get the craterlets to appear entirely within the frame, and got new somewhat more accurate data for all the craterlets I labeled on my original image:

LUNAR ORBITER RECONNAISSANCE CAMERA
CRATER DIAMETERS FOR SELECTED CRATER PITS
INSIDE THE LUNAR CRATER PLATO

(diameters +/- 0.02 km, measured from rim crest to rim crest)

Craterlet A: 2.51 km (1.56 miles), Craterlet B: 2.00 km (1.24 miles)
Craterlet C: 2.21 km (1.37 miles), Craterlet D: 1.95 km (1.21 miles)
Craterlet W (west wall): 3.14 km (1.95 miles),

Craterlet e: 1.73 km (1.07 miles), Craterlet f: 1.46 km (0.91 miles)
Craterlet g: 1.40 km (0.87 miles),
Craterlet h (triple crater feature 2.24 km x 1.19 km (1.39 miles x 0.74 miles))
components "h-1": 1.19 km, "h-2": 1.08 km, "h-3": 0.79 km

Craterlet i: 1.27 km (0.79 miles), Craterlet j: 1.09 km (0.68 miles)
Craterlet k: 0.95 km (0.59 miles), Craterlet l: 0.94 km (0.58 miles)
Craterlet m: 0.91 km (0.57 miles), Craterlet n: 0.87 km (0.54 miles)
Craterlet o: 1.10 km (0.68 miles)
Craterlet p (triple crater feature approx. 1.8 km x 1.5 km (1.1 mi. x 0.9 mi.))
(components: p1: 1.27 km, p2: 1.04 km, p3: 0.57 km)

Craterlet q (doublet): 0.78 km (0.48 miles)
Craterlet r: 1.19 km (0.70 miles)

Some of the craterlets may be more detectable at lower sun angles due to their more prominent ramparts which extend probably at least 15% to as much as 30% of the crater diameter beyond the actual rim point. This could make them appear larger than their physical rim-to-rim diameters would indicate. For example, the central "A" craterlet is 2.51 km from rim to rim, but from rampart base to rampart base, it is closer to 3.3 km. Indeed, I have seen the "bump" of Craterlet A in Plato with only an 80mm aperture, although clear evidence of the "pit" was not seen. The shadow from one of the rims/ramparts at a very low low sun angle can also make the craterlet appear somewhat larger than when the sun is higher above the lunar horizon. You might see a black dot of the shadow along with a hint of the lighter area up-sun from the up-sun rampart which again, might let you see what appears to be a craterlet fully-resolved. At high sun, of course, you could probably see the lighter albedo of the craterlet and its ejecta blanket at apertures less than that needed to fully resolve the craterlet under low sun angle. Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6313266 - 01/14/14 09:43 PM Attachment (12 downloads)

David, thank you for the discussion. Yes, Dawes is an empirical and approximate limit applicable to stars of a given magnitude. This is why I was referring to Lambda/D as an approximation to Dawes and FWHM. It's reasonably close for a given range of moderate magnitude point sources.

While you cannot modify Dawes, per se, since it is such an empirical limit, the Airy disc dimensions are altered somewhat by the presence of the central obstruction both in terms of peak central intensity due to obscuration and diffraction radii (including the Airy disc radius) due to added diffraction not present in an unobstructed aperture. So, while you really cannot modify Dawes as you say, you can modify Lambda/D as an approximation for Dawes. The amount of modification is unclear, it changes for coherent light and incoherent light.

Quote:

The amount of energy put into the first ring by the obstruction would negate any alleged resolution increase on extended objects, reducing the contrast on high power planetary images and rendering small shallow craterlets near the resolution limit of the telescope more difficult to see.



Yes, I think you are exactly right. Crater floors will be grayed out when they are near the limiting resolution of an aperture. Whether sufficient contrast remains at a given angular diameter is the entire issue. At some point, there is just not enough contrast remaining to resolve the crater floor from any rim brightening or even the general albedo in the area. But is the first ring the culprit or the are brighter central discs finally coming into contact at very small angular diameters. I think you can see 'through' the brightness of the rings (relative to the brightness of the rim) provided the floor has enough contrast and a sufficient angular diameter approaching the Raleigh limit. Maybe even close enough to Raleigh to call that limit in general. Plato is a great place to check this out. My hypothesis is it requires a larger crater diameter, maybe even only by 1/10th or 1/5th of a mile.

I can only assert that there is likely some effect noted viewing doubles near the Dawes limit and slightly below. In diffraction limited seeing, I feel strongly there is room to shave a few hundredths of an arc second from those tight pairs leaving a lesser dark space between them (and given the errors in their recorded separation.) That accords with theory and, again, is highly dependent of the degree of coherence of light observed (which is neither totally coherent nor incoherent.) And it depends on the seeing, too, it cannot add any significant induced aberration to the final image.

An obstruction does have an effect, it's just hard to say exactly how much of an effect. This is the phenomenon that gives the MTF a boost at the highest spacial frequencies over that of a perfect obstructed aperture. So, you can apply the presence of an obstruction to resolution thereby besting the Dawes limit from ~0.91 (approximately Dawes) spacial frequency out to as much as 1.1 spacial frequency (in theory) beyond the spacial frequency normalized 1.

The thing that bugs me is having seen "e" at 1.07 miles. It's angular diameter of course changes with lunar distance, but it's still near 6.3/D. I would be curious to know if it can be resolved in an unobstructed 150mm aperture being that close to Raleigh against a darker floor.

Anyway, David, I do appreciate the discussion. It's a fascinating topic and challenge to explore in theory and in practice.

Edit: Below is an excerpt from a spread sheet (attached) for a 150mm scope using the small angle formula, it shows a difference of about 1/10th of a mile difference between obstructed and unobstructed in theory at Raleigh.

Mean 238855 Miles Theta =0.92" arc d=1.07 Miles Resolved unobstructed d=0.97 Miles Resolved obstructed.

A 6" obstructed can see "e", I have seen it. In theory an unobstructed scope could too just barely in excellent, diffraction limited seeing at 8/10 Pickering or better.



Edited by Asbytec (01/14/14 10:25 PM)


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Re: Plato's challenge new [Re: Asbytec]
      #6313287 - 01/14/14 09:51 PM

Quote:

" The realitive effects from aperture and aberrations on such image will be realistic, but its not what you would encounter at the eyepiece."



Its not clear what they mean by this, do they mean we will not see the diffraction effects as shown? Or do they mean don't expect to see the pattern so clearly due to seeing? I will admit I've had a hard time getting Aberrator to put up patterns that are exactly what I see at the eyepiece, so the latter may be true.

But, as an approximation, it does pretty well with a scaled very good image of Ganymede when applied to an aberrant and obstructed 150mm aperture. Maybe not perfect, but pretty darn close, actually. So, I trust it as far as I can throw it. The image above might not be perfect, but it has characteristics that make it look pretty darn close including the grey floor of a 1" arc craterlet when applied to a 150mm aperture. That is consistent both with my experience and from what I can gather from theory.


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Re: Plato's challenge new [Re: Asbytec]
      #6313416 - 01/14/14 11:26 PM

Asbytec posted:

Quote:

Its not clear what they mean by this




Yes, it is quite clear. The relative effects of central obstruction or aberrations on an image are fairly accurate, but the view will not match that of a given aperture on an actual planetary object. You put in an image of the given object and *not* the actual view of the object itself in that given aperture. In other words, it demonstrates the effect of the degradation caused by obstructions or aberrations on a given image, but does not precisely duplicate what is seen with the actual view with the *real* object. That would require an accurate lower-contrast image that matches what could be obtained with perfect optics and the human eye. This isn't what the program uses (and the limit of 10 pixels per arc second really kills the ability to simulate smaller features).

Quote:

But, as an approximation, it does pretty well with a scaled very good image of Ganymede when applied to an aberrant and obstructed 150mm aperture.




Huh?? Are you saying you have actually seen detail on Ganymede in a 150mm MCT?? Ganymede in a 150mm aperture is basically a featureless disk less than 1.84 arc seconds across. This is *especially* true of a 150mm scope with more than a 30% obstruction (Ganymede's angular diameter is only roughly the diameter of the diffraction disk of a star in a 150mm aperture and not much larger than a bright star's spurious disk). Even in my 9.25 inch SCT near opposition, I can only get the vaguest hint of a bit of darkening in one small area on Ganymede at over 400x. My 10 inch (21% central obstruction, 1/19th wave p-v wavefront primary) does slightly better on showing a vague darker area on that moon, but that feature is of *very* low contrast. Otherwise, there is very little obvious detail on Ganymede in that aperture. In my 14 inch Newtonian (22.5% central obstruction) I can see a little more, but the shadings (when they are visible) are still quite subtle. They have far lower contrast than the heavily stacked and processed CCD images of that moon taken by Damian Peach in his 14 inch telescope. Aberrator is a useful piece of software, but not for simulating what the views of real objects or small scale lunar features will look like precisely when viewed by the eye through the telescope. Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6313710 - 01/15/14 05:47 AM Attachment (13 downloads)

Quote:

Huh?? Are you saying you have actually seen detail on Ganymede in a 150mm MCT??



One of the reasons I am a believer in theory is having seen it working as advertised. But, absolutely a 150mm can resolve features on Ganymede.

I guess it depends on what you mean by resolved, though, and what features are observed. Nothing is perfectly clear and distinct like an image, but you can see Osiris and Phrygia Suclus as brighter specks dancing near the limb easily enough. Any darker features are just that, maybe a bit if very indistinct darkening approaching the limb and nothing more. No riles, no patches, nothing other than a darker hemisphere than the other. I will say, however, that the dark feature Perrine Regio was totally not seen even though it looks possible. As you say, it apparently has not enough contrast. So, outside of a darker hemisphere, I doubt 'real' dark feature resolution can be done easily.

So, dark features maybe, but bright craters are definitely seen on Ganymede.

You're description of seeing with 9 and 10" aperture sounds reasonable and more like a bit higher resolution of those apertures. I can only credit this to excellent tropical seeing conditions, but the brighter craters are there to be seen and maybe, just maybe, a slight hint of darkening. Eddgie can see darker features more clearly in his C14, to me its just a very weak darkening to some point on the disc. I doubt it's as good as your 9 and 10" scope show it, but it is detectable.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6297950/page...

Io has some distinctness about it, too, but nothing "resolved." Those are two Jovian moons a 6" can show as something other than a disc.

Yes, apparently you can resolve detail on an object the diameter of the Airy disc provided, as you say, contrast is large enough (or maybe expansive enough, too.) More to the point, though, the same resolution behavior should exhibit itself on the moon, even though we're not dealing with a single Airy disc (Ganymede might be more than one Airy disc, too, but it's at least an expanded PSF with peaks of varying brightness 4x larger than an optical point source.)

Yea, please don't misunderstand. I agree with you Aberrator is probably not perfect working with extended objects. But it's amazingly close. Here's one of Ganymede with an aberrant 6" applied. Not bad, even though the dark Regio Galileo is better resolved in this image than in the real world, Osiris is plainly visible.

I'd expect similar results with craterlets on Plato's floor. In fact, I am hoping folks report such findings.


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Re: Plato's challenge new [Re: Asbytec]
      #6314366 - 01/15/14 01:07 PM Attachment (12 downloads)

Asbytec wrote:

Quote:

One of the reasons I am a believer in theory is having seen it working as advertised. But, absolutely a 150mm can resolve features on Ganymede.




I am sorry, but a 150mm aperture cannot resolve *any* features on Ganymede. It is utterly impossible, as the diffraction effects in a 150mm aperture will totally obscure *any* detail on that moon (especially with a whopping 31% central obstruction making things even worse). The diffraction disk of a star in a 150mm aperture and the disk of Ganymede are just too similar in size to allow anything to be even remotely detected on that moon's tiny disk (see diagram below). The telescope simply isn't large enough to pick out any real detail on Ganymede. In fact, at only a 150mm aperture, the aperture is just barely large enough to make the disk of Ganymede itself become resolvable rather than just blurring into a spurious disk in the diffraction pattern of a star-like object. Any detail you might seem to see on Ganymede in a 150mm aperture is totally illusionary, possibly caused by the "noise" of the eye/brain system (or perhaps some seeing effects). It isn't real detail.

I'm afraid that if you believe you see detail on Ganymede with such a limited aperture, this might make me wonder just a little bit about your alleged sightings of the e craterlet in Plato. Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6314833 - 01/15/14 04:14 PM

Not true actually Dave. SKY & TELESCOPE some years back had an article about Gary Nowak seeing a polar brightening with a 6" Apo . I duplicated that observation with my 8". The illustration is accurate you portray but the airy disc size comparative isnt representing contrast resolution that can be seen smaller than its radi or diameter. A stellar diffraction pattern is a different matter altogether.

I think you are misunderstanding resolution Dave.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6314963 - 01/15/14 05:29 PM

There appears to be a deficiency in David's diagram: in practice there is a significant brightness gradient in the inner region of the Airy disc, and consequently it doesn't seem unreasonable to be able to resolve high contrast features which are around half the diameter of the Airy disc. I prefer to think of the extended object resolution threshold of an instrument as about the Rayleigh limit (5.45 arc sec divided by the objective diameter in inches). The presence of a central obstruction of the size typical of reflecting or compound instruments of the type likely to be used for lunar/planetary observation really doesn't make much difference, the contraction of the Airy disc with increasing CO being offset by contrast loss.

Anyhow the highest contrast "feature" there is to see on any of the Galilean satellites of Jupiter is the contrast between lit and unlit portions during the beginning or end of an eclipse. At mid eclipse the satellite should show a perfect half phase. Experience is that this is seldom if ever seen with 6" of aperture ...


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Re: Plato's challenge new [Re: azure1961p]
      #6315161 - 01/15/14 07:02 PM Attachment (16 downloads)

Quote:

Not true actually Dave. SKY & TELESCOPE some years back had an article about Gary Nowak seeing a polar brightening with a 6" Apo . I duplicated that observation with my 8". The illustration is accurate you portray but the airy disc size comparative isnt representing contrast resolution that can be seen smaller than its radi or diameter. A stellar diffraction pattern is a different matter altogether.

I think you are misunderstanding resolution Dave.

Pete




No, I am not misunderstanding anything. We are talking about "detection" of detail. People claim to see all sorts of things right at the limits of visual observation (even in Sky and Telescope), but in this case, the physics of the situation kind of trumps the observation. I do fully understand resolution (I have a B.S. in Physics/astronomy). Detection of very low contrast non-linear detail that is significantly smaller than the stellar diffraction disk diameter for a given telescope is just not possible because the diffraction effects that create the pattern tend to obscure that detail. Reliable claims of observations of detail on Ganymede were first done with apertures larger than six inches (example: observations by H. Camichel, N. Lyot, and M. Gentil, using a 15.2 inch (38 cm) refractor on Pic-du-Midi in 1941). Claims of observations of detail on Ganymede in a 5.9 inch Mak-Cassegrain with a whopping 31% central obstruction are very highly questionable to say the least. It also isn't a question of pure resolution either. The magnification needed to get a 1.8 arc second object up to something even half the apparent size of the full moon would be 500x, which would yield a very dim image of that object in only a 5.9 inch telescope. That aperture would have to approach 50% larger (say, something larger than eight inches) for such an observational claim to be even slightly credible.

As for my diagram, for demonstration purposes, it is reasonably close to being fully correct. The central bright disk seen with stars at high power is *not* the "diffraction disk" (and some authors don't even call it the "Airy" disk either). The diameter of the diffraction disk is defined as the diameter of the central diffraction pattern *at the first minimum* of the pattern (the first minimum is the very center of the first dark ring out from the bright central "spurious" disk). For an unobstructed 150mm aperture in visible light, this is 1.845 arc seconds (twice the Rayleigh Criterion figure of just under 0.923 arc seconds). For a 31% obstruction, the first minimum's diameter is slightly smaller at about 1.677 arc seconds, but as can be seen by closely examining the diagram I created pixel by pixel, the 1.8 arc second drawn disk of Ganymede (72 pixels wide) is still just slightly larger than the first minimum of the adjacent star diffraction pattern (67 pixels wide). The largest Ganymede ever gets is around 1.8 arc seconds and right now near the current opposition, it is 1.72 arc seconds across. This is so close to the size of the diffraction disk (and not all that much larger than the bright central "spurious" disk of a star's diffraction pattern) that the effects of the way light is forming that pattern will obscure detail significantly smaller than that diffraction disk's size. Sorry, I just don't buy claims of detail being visible on Ganymede in modest apertures like a mere 150mm. Clear skies to you.


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Asbytec
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Re: Plato's challenge new [Re: David Knisely]
      #6315283 - 01/15/14 08:02 PM

I would think the spurious disc (not the Airy disc) would be the smallest resolvable feature possible, yet we can see objects 4x smaller than the Airy disc.

To begin with, the spurious disc is already about half the diameter, so you're halfway there, already. In point source resolution without a black space, there is plenty of empirical evidence suggesting very tight double stars can be 'resolved' down to 0.5 times the Raleigh limit - 1/4th the Airy disc diameter. (My personal best is 0.62 times Raleigh limit no doubt influenced by the presence of an obstruction, as is the case with 7 Tau easily split with sufficient dark space to indicate something smaller than Dawes is possible.)

At this spacial frequency, there is not sufficient contrast between to brightly lit spurious discs to show a dark space for hard resolution. And we're well beyond Dawes at this point, anyway. This is a different animal than an extended object, but the example shows the Airy disc is not the limiting feature we think it is.

As an extended object begins to exceed 1/4th the Airy disc diameter (the working definition of an optical point source), it's PSF begins to expand noticeably. When the disc radius is equal to Lambda/F it's FWHM (which is an approximation of what we see near Dawes) is much larger than the PSF of the point source Airy disc at FWHM by a factor of two. In other words, Ganymede is twice the diameter of the spurious disc leaving plenty of room for a high (enough) contrast feature to offer an Airy disc of it's own superimposed on the twice as large FWHM of Ganymede.

It's in the form of a gradient, as Brian says. The high contrast bright feature can peak above the surface intensity of Ganymede, as I understand it. And if the peak is high enough (contrast), such a bright object can be seen on the expanded PSF on an object of Airy disc diameter (whose PSF is twice FWHM of a point source Airy disc.) A dark object, too, if it's of sufficient contrast. Otherwise it might appear as an intensity fall off on one hemisphere if the feature is large enough. Galileo Regio is pretty large and seen as a less bright hemisphere (or limb shading), Perrine Regio is not large and was not seen.

If you have ever seen the diffraction rings around Jovian moons, you will note Io and Europa are more star-like in appearance. Ganymede's rings are more washed out indicating it is, indeed, not a point source and therefore does not offer a point source PSF. Io and Europa are at a diameter that is roughly 1" arc, or about half the Airy disc diameter, and their PSF is barely enlarged beyond that of a point source.

One might even resolve a very high contrast feature on either Io or Europa if one existed on their surface. The resolution would be very difficult and very similar to a very tight equally bright double with a separation near half the Raleigh limit. Io does appear elongated and this may be the cause. Resolution on Io? Surely I jest () I dunno, maybe. Depends on the definition of resolution. Maybe from the behavior of its PSF we can say we resolved it's brighter equator from its darker poles even though we cannot see what's actually going on. Nothing is actually 'split', it's simply elongated.

That's theory and accords with my experience with two bright crater 'specks' seen on Ganymede's surface when seeing is at least diffraction limited. Any induced aberration makes detection that much more difficult.

This is high resolution applicable to lunar observing where contrasts are very high. You are correct, the obstruction makes a tiny difference of about 10% in the realm of the very tiny (near the Airy disc and inside the first ring.) That is a difference between resolving a crater that subtends 1" arc and one that subtends 0.9" arc (which turns out to be a the difference between crater about 1.1 mile in diameter and one that is 1 mile in diameter at the lunar mean distance.) It minor, but doable when your scope is operating in near lab like conditions in the real world. I have seen both "e" on Plato, and IIRC, one closer to 1 mile elsewhere, and surface high (enough) contrast features on Ganymede.

Edit: I was upwards of 400x on Ganymede. Of course, there is no further resolution to be had, only image scale and brightness as you say. But, the relative contrast should remain unchanged and the dimming does have (unknown to me) physiological effects. Being up that high didn't seem to hurt anything, it was just easier to look at. I'd assert the presence of an obstruction was helpful, if minor. It was minor enough.

Anyway, it's a great discussion and I think it applies directly to the high resolution needed for small Plato craterlets.


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Asbytec
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Re: Plato's challenge new [Re: Asbytec]
      #6315341 - 01/15/14 08:31 PM

Quote:

...and consequently it doesn't seem unreasonable to be able to resolve high contrast features which are around half the diameter of the Airy disc.



Brian, I agree Raleigh is in the ball park for resolution of features with sufficient contrast. Certainly 100% contrast with about 28% remaining contrast transferred. It is likely more difficult on the moon itself and Plato in particular cine object contrast is lower. This threatens Raleigh limit as a limit for extended objects, but if two points leave 28% contrast and it appears black then lunar features of that angular separation can leave something less than 28% final transferred contrast and appear grey.

Yes, the first bright ring (mostly) does seem to make any high contrast features, such as a crater floor, much more grey than black provided it is of a dimension that is lies under those rings in a very complex way. As long as that grey is a different level than it's surroundings, maybe by about 5% in accord with Dawes, then that crater floor should be seen if it is large enough to separate the brighter (and infinite number of) spurious discs in the vicinity.

On your quote above, actually I'd think you could see anything smaller than 1/2 the Airy disc diameter for bright sources all the way down to a geometrical point provided it is bright enough. It will form it's own spurious disc that will be about half the diameter of the Airy disc. Imagine being able to 'resolve' geometrical points on the lunar surface or Jupiter, for that matter. Now that's some resolution when you can 'resolve' points on an extended object.

But we should see them in the same way we see stars - as spurious discs at about FWHM when the extended object disc is at least FWHM or larger - if transferred contrast is sufficient, as you say. On the moon, this could affect the detection of crater specks. We might not know how small they are, we'd only know how bright or how much contrast they offer. One might imagine they'd have to be of some diameter and albedo to reflect enough light putting up enough final contrast.

Fascinating discussion...the proof lay on Plato's floor.

Edited by Asbytec (01/15/14 08:41 PM)


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azure1961p
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Re: Plato's challenge new [Re: David Knisely]
      #6315537 - 01/15/14 10:19 PM Attachment (19 downloads)

I would still disagree (funny because Im not the one making the observation with 150mm but I haven't tried either) .

Buddy, seeing a half a Ganymede , or rather a crescent of Ganymede via an eipse by another Galilean moon was actually had with a 4" apo as reported on thes boards by Buddy Barby. It goes back a couple years but I recall his reporting that quite clearly. And mind you, he wasn't seeking it out as a threshold achievement infact he didn't expect to see such a thing but alas, he reports he had.

David, The trouble that's muddying thes waters is that a stellar diffraction pattern is created by a virtual point source. Ther can be no such contrasts - even if there were to be had from such a minuscule point - hence the pokerface diffraction pattern. By contrast (literally) the surface area of a galillean moon is a different dynamic altogether. Its not a virtual point source at all and the area subtended (granted beyond the angular res if the aperture) is producing a sizable surface area light at any point .

Take Io for example. Before there was a CN with an imaging forum packed with egg shaped Io images, Pickering saw it as ovular with a 5" aperture - not even a 150mm. By using the eclipsed Ganymede as an example though Brian you could say that Pickering couldn't possibly detect the polar darkening evidenced by the ovular Io he observed. Of course he didnt realize it was albedo effect at the poles he assumed it was egg shaped in fact. The truth of course is Pickering with the 5" refractor was RESOLVING the lesser albedo of the poles (however crudely) - and on a disc virtually 1" across. A far greater feat than seeing a half a Ganymede in semi-eclipse.

The trouble here is the moons aren't stars and while diffraction effects certainly serve to mask contrasts it doesn't obliterate them to the degree of absolute erasure. Pickerings Io observation is strong evidence of that this is the case . The fact that Io's poles are hardly black like that of an semi eclipsed Ganymede and it underscores the point. Merely darker material was enough to change the apparent shape of the object. When you factor in the understanding the brighter equator of Io is only about 0.3 to 0.5 arc second this should have been completely missed in such a hole aperture.

I'm bypassing Norme here and going for Pickerings example as its from a time when no high res images were available of course and so that observer couldnt be fooled by prior suggestion.

I respect both of you but Ive got to disagree .


Pete

Edited by azure1961p (01/15/14 10:21 PM)


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David Knisely
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Re: Plato's challenge new [Re: azure1961p]
      #6315705 - 01/16/14 12:25 AM

azure1961p wrote:

Quote:

David, The trouble that's muddying thes waters is that a stellar diffraction pattern is created by a virtual point source. Ther can be no such contrasts - even if there were to be had from such a minuscule point - hence the pokerface diffraction pattern. By contrast (literally) the surface area of a galillean moon is a different dynamic altogether. Its not a virtual point source at all and the area subtended (granted beyond the angular res if the aperture) is producing a sizable surface area light at any point .

Take Io for example. Before there was a CN with an imaging forum packed with egg shaped Io images, Pickering saw it as ovular with a 5" aperture - not even a 150mm. By using the eclipsed Ganymede as an example though Brian you could say that Pickering couldn't possibly detect the polar darkening evidenced by the ovular Io he observed. Of course he didnt realize it was albedo effect at the poles he assumed it was egg shaped in fact. The truth of course is Pickering with the 5" refractor was RESOLVING the lesser albedo of the poles (however crudely) - and on a disc virtually 1" across. A far greater feat than seeing a half a Ganymede in semi-eclipse.




With the eclipse, you have a very high contrast large-scale feature (the shadow of another Galilean moon) which is a good percentage of the diameter of the moon itself. That is not the case with finer albedo features on the Galilean moon's surface. The times when I have seen even a hint of albedo features on Ganymede, it was using my 9.25 inch and 10 inch apertures. They were hardly obvious in those apertures (pretty darn marginal in the 9.25 inch SCT actually), so I really have a something of a problem believing that much if anything of them can be seen in a 150mm aperture (especially one with such a large central obstruction). Probably the best view I ever got of the Galilean detail was during a transit of Ganymede across Jupiter, as then, you could see both the color and variable intensity of that moon's disk. Against the black background of space, it wasn't nearly as obvious. Shadows or large-scale high-contrast albedo features are one thing, but Ganymede's surface markings are somewhat different.

It would be a lot easier to get back to talking about craterlets on the moon, where the contrast is frequently fairly high even at some physically small scales. Clear skies to you.


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Asbytec
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Re: Plato's challenge new [Re: David Knisely]
      #6315998 - 01/16/14 08:49 AM

Pete, you can bypass me all you want.

Retracing Pickering's observations was an enormous treat, a taste of history repeated. You were there as was Jason and Edggie, et al. I thank Jason Berry for bring the subject up, something I never thought possible. But it is, Just as Pickering claimed. He may not be a nut case, after all. Maybe I am.

I respect everyone who's participated in this discussion and have a deep appreciation for David's lasting and meaningful continuations. And he's right, this is a topic of Plato's craters. We should be discussing that. Barring that, however, we can talk about resolution for a bit because it pertains to Plato while we wait for observations to trickle in.

Pete, you are so right, though. Pickering did not know what he was looking at. We do, but that makes repeating his observation no less exciting. And diffraction does hamper observation, we just have to know at what point this is so.

As I've said before, with emphasis, this is a great discussion and I look forward to reports, once again, from Plato. Not only is it exciting, but we can learn a lot about ourselves and our equipment. And theory and the real world.


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Re: Plato's challenge new [Re: edosaurusrex]
      #6317564 - 01/16/14 10:36 PM Attachment (20 downloads)

Looks like "JAN 22 2214 SETTING" is the next opportunity to observe Plato. It's late in the evening, so maybe seeing will improve somewhat.

Maybe at this sun angle, enough of the craterlet floor will be dark allowing resolution, too. At higher sun angles it would appear that contrasting darker shadow would be minimal and probably fall below Raleigh limit for the smallest craters.

David, above you refer to the CO as a brighter first ring effect. That's correct. Its interesting I think of the CO affects in terms of smaller spurious disc. Both are minimal, and maybe the smaller disc is more minimal. Both can have an effect of offering less contrast on the crater floor but allowing us to resolve slightly smaller until that crater floor is lost in the balance of both effects.

By the way, don't forget Plato's albedo. It can be quite challenging, too. Below is my visual impression and cannot swear it matches images very well.

Edited by Asbytec (01/17/14 12:45 AM)


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Asbytec
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Re: Plato's challenge new [Re: Asbytec]
      #6317810 - 01/17/14 01:57 AM Attachment (22 downloads)

Back to Ganymede and the topic of resolution as it may relate to Plato for a moment. Here is an image of Ganymede taken with an 8" SCT. It's not a clear image, but it tells me the contrast is on the focal plane. Otherwise the camera would not have been able to detect and enhance it. And if enough contrast is on the focal plane, it can be seen by the human eye, too, though clearly not nearly as well as the image.

Also, note the level of resolution available with an Airy disc ~1.4" arc in diameter (or maybe closer to 1.2" arc obstructed) on a disc ~1.8" arc in diameter. Clearly resolution below the level of the Airy disc (smaller by ~0.4" arc than a 6" aperture) is already well underway on an a extended object not much larger than the Airy disc itself. This suggests resolution is also occurring within a 6" Airy disc, albeit more weakly.

Below is an Aberrator simulation of Ganymede through an 8" aperture. It probably resembles, though not perfectly, closely the human eye response than a processed image. Maybe some processing of this image might reveal something similar to the image above, if the image below contains the dynamic range necessary.

But, this just shows what smaller apertures can do near the Raleigh limit. I expect similar results on Plato if anyone reports them in the coming weeks.


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edosaurusrex
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Re: Plato's challenge new [Re: Asbytec]
      #6319252 - 01/17/14 06:52 PM

The sunset time is when the Sun's altitude will be 12 degrees at Plato's center and getting lower. Start looking for the craterlets before the sunset dates.

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Asbytec
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Re: Plato's challenge new [Re: edosaurusrex]
      #6319427 - 01/17/14 08:51 PM

Okay, a couple of nights prior, maybe tomorrow. If the weather will ever clear, again, within the span of a human life time.

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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6319634 - 01/17/14 11:10 PM

The sim looks close - but my observations are too long ago when I had good seeing 9-Puckering or better . I do recall with utter certainty on of the poles appearing like it had a polar cap - about 25-30 percent of the disc from the pole end - somewhat like a Martian polar good. That particular night ( being the best ) I had the serendipity of seeing the exact same image the next day online the following morning by the owner if excelsior optics - Mauro D. He photographed more than I saw with my eye (with a ten inch newt) but the polar brightening was spot on. Other times I had seen vague shadings - without the saturday morning serendipity if a follow up photo ( this is prior to CCDs catching on as big as now) The image you link to gives a nice feel for the size of the details that are visible , though a darn sight more pale! With some advice from on of the experts he did less processing and farther down the page his image is clearer. I don't think Im getting 9 Pickering anytime soon this winter so it may be a while before I can duplicate those sightings. An interesting topic nonetheless.

Other observers who've seen details on Ganymede with medium apertures is Carlos Hernandez with his 9" Mak and David Gray with a 10" f/7 newt.
Both were able to actually see fine streak like details . I'm happy with the polar hood look!

Pete


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Re: Plato's challenge new [Re: Asbytec]
      #6333160 - 01/24/14 04:41 PM

wait wait wait, it has mini craters?!

I need to go setup, bbl


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Asbytec
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Re: Plato's challenge new [Re: OrlandoMatt]
      #6333776 - 01/24/14 10:48 PM

Quote:

wait wait wait, it has mini craters?!

I need to go setup, bbl






Report back. I missed my chance on the 22nd. But, I guess the mini craters are still there. Dunno, haven't seen them in a while.


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azure1961p
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Re: Plato's challenge new [Re: OrlandoMatt]
      #6335829 - 01/25/14 11:59 PM

Quote:

wait wait wait, it has mini craters?!

I need to go setup, bbl




Sure does but boy they are not easy.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6338826 - 01/27/14 01:48 PM

Being new to the moon and remembering it being the first thing I saw as a kid; Plato is easily one of my favorite objects! It's just so round! Anyways I'm really going to investigate it after all the info in this thread. I'll report back soon!

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azure1961p
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Re: Plato's challenge new [Re: OrlandoMatt]
      #6339809 - 01/27/14 10:13 PM

Plato is one of those great potential areas for me that I consistently miss best lighting for. Either its way too dark and shadow cast or the lighting more often then not at my observing hour, is so steep its pointless. Its just off in longitude enough my schedule rarely allows for a great lighting opportunity when I can observe it. The challenges are there and craters all the way down to invisibly small but I'm usually witness to the bright four or five.

Pete

Edited by azure1961p (01/27/14 10:15 PM)


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photonovore
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Re: Plato's challenge new [Re: azure1961p]
      #6340125 - 01/28/14 02:38 AM

Set up your 6" scope in a field and set up a target board. Have an assistant put up alternate sheets of white paper with one of the following symbols(each equal diameter)upon each printed in black-- show to the observer in random order and multiple times (including intermittently repeating the same figure)--and sized/at a distance which equals ~1-1.5"arc apparent angular dimension:

c e a o @ *

or make up some little disc graphics with "bites" out of cardinal parts of the circumference with a crescent or two thrown in for good measure.

Attempt to identify each individual symbol as it is presented and compile the results and correlate.

You will end up with an answer as to what you can and cannot resolve with that telescope at such an angular dimension--this with nearly perfect "seeing" and with near perfect contrast. If you only make a hash of consistently identifying the various figures in this exercise you can rest assured that anything in the sky of similar angular size within which you *think* you are seeing detail... you certainly are not.


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azure1961p
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Re: Plato's challenge new [Re: photonovore]
      #6340351 - 01/28/14 08:12 AM

A way to condense or shorten the distance if this set up is to use a reflective ball like a silver Christmas bauble with the reflection of the words within it. By breaking the baubles size down by degrees and arc seconds per its diameter you can get the size of the type or letters, fonts, whatever. If say the larger but farther the symbols are from the bauble the better so as not to get fisheye distortions. I mention this because doing it another way can be really hazardous to the image with ground thermals boiling away the details . The bauble closes this distance for a cassegrain of 6" to under 100 yards . You could focus nearer but then the mirror spacing for near focus introduces SA aberrations.

Pete


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Asbytec
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Re: Plato's challenge new [Re: photonovore]
      #6340484 - 01/28/14 09:29 AM

Quote:

If you only make a hash of consistently identifying the various figures in this exercise you can rest assured that anything in the sky of similar angular size within which you *think* you are seeing detail... you certainly are not.




It's an interesting test, in near lab like conditions, if someone wants to conduct it. It'll tell you what you should be seeing if real world seeing is diffraction limited. I might be interested to perform it to know what is possible in the "lab", rather than what is probable in the real world. When seeing permits, what is probable comes pretty close to what is possible. If 1", for example, is well within what is probable, then something smaller might be possible.

The moon, actually, is such a target at a known distance with 1" and smaller features on it. When seeing is diffraction limited one can discern, minus the ambiguity of various and random characters, familiar features such as craterlet floors. There may be some level of "thinking" we see it, but experience will be a good guide as to whether that fluttering dark spot is a crater floor or not. Then you can say, "you certainly do."

As a hypothesis, experience tells me I could easily discern o and c at 1" arc. Letters a and e will likely be grayed out, and might be able to see the larger space in the lower half of the a. There's probably no chance of resolving the more narrow space in the upper e, but the e might be discerned as such, anyway. The ampersand might show a white feature in it's center, but I doubt the double arcing lines will be resolved. The asterisk will likely just be a dark spot. It would be interesting to note whether the asterisk's spikes can be resolved.

Successfully and knowingly observing sub arc second features on both Jupiter and Ganymede in diffraction limited seeing have given me the experience to know about what my scope and acuity can do. A similar test with pin points simulating double stars might be interesting, though. Maybe this rainy season, right now Jupiter awaits on the zenith and I await the last of the day's clouds to vanish.

Anyway, the thing is, the difference between thinking we saw something and knowing we saw something just come with experience and personal integrity. If I resolved the space in the upper e or the spikes on the asterisk, would anyone believe it? Not until they tried it themselves, and probably dependent on whether they succeeded or failed.


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6342092 - 01/28/14 11:19 PM

Frankly its a little pointless to test if you know you saw it then all it becomes is someone inventing a test to test YOU.

It is the lousy downside of observational astronomy in deepsky or lunar/planetary and stellar. As Stephen James Omeara pointed out some time ago (after hearing Barbara Wilson being told she was imagining things) we have to learn to realize we don't all see with the same eyes and brain and its a sober fact some can see what others can't. There's a limit in this too - I don't believe an astronomers reports of ultraviolet and infrared details.

This usually gets ignored but one of the chief abilities of the better visual observers is the brains response time - processing stimuli faster than most. Its also sonethibg that can be improved through training (more observing).

Pete


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photonovore
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Re: Plato's challenge new [Re: azure1961p]
      #6342262 - 01/29/14 02:07 AM

Quote:

Frankly its a little pointless to test if you know you saw it then all it becomes is someone inventing a test to test YOU.






Only if you have delusions of infallibility I suppose. For myself, I like to check myself: anyone is susceptible to erroneous self-validation...


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Re: Plato's challenge new [Re: photonovore]
      #6342339 - 01/29/14 04:00 AM

Mardi - you *cannot* possibly convince these eagle-eyed guys to conduct any objective experiments: they claim to see details on *Ganymede*, so the Moon should merely be a walk in the park

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Re: Plato's challenge new [Re: Mare Nectaris]
      #6342581 - 01/29/14 09:01 AM

Those who don't trust themselves are missing so much. Those who think such things are impossible are doomed not to enjoy them. You simply have to observe Ganymede on a good night to believe it, preferably when one of its brighter craters is visible.

Here's one you surely won't believe. Try observing the 'apparent' elongation of Io. It can be done with at least 150mm aperture in diffraction limited seeing. But, don't take my word for it. Pickering urged folks to observe it in modest apertures about 5" or so because he knew it could be observed. I know it can be done - having seen it. It's not easy, but it's not impossible.

Same with lunar craters. There's no mistaking a tiny dark shimmering craterlet floor when it's there. It's a test, a real world test. It does not require delusions of infallibility when, indeed, marginal observations can be achieved with confidence.

It is really too much to believe craterlet's a through E and W can be resolved in crater form in a small scope without a conducting a test to check yourself? I'm waiting for folks to observe them and prove it can be done.

More folks should observe such things when conditions permit. Ganymede should be common knowledge instead of a doubtful mystery. Io is a little tougher, but it should be common knowledge, too. Craterlet's a through E and W should be on everyone's checked off observing list - not just mine.

If you doubt, try it. Trust what you see, trust yourself. If not, you're missing out on so much. Often times I trust the view of a faint festoon, and just as often it turns out reasonably close. That's a confidence builder and a verification of one's infallible delusion.

It's not so much about being eagle eyed as it is about operating in conditions where a cooled and collimated aperture is the limiting factors, taking the time to actually observe something, and trusting your observation regardless whether others trust it or not.

I still cannot see bands on Uranus and might have glimpsed a small stretch of the Alpine rile exactly twice in three years. Sometimes I see oval 7a, sometimes not. Sometimes 42 Ori is easy, other times it's a tough call. Thought I saw Enke's once, turns out it's essentially impossible and a real let down. Observation varies widely and it can be fallible ONLY if you make a bogus call.

So, who's gonna observe Plato, anyway, and find out what they can or cannot see instead of bantering about it? This is the observing forum.


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6342627 - 01/29/14 09:23 AM

Mare Nectaris,

Ganymede is NOT a difficult object to detect contrasts on when the seeing permits. Its not glaring but its not unbelievably pale either - just subtle. The point here is the seeing. If I get one or two great nights like that in a year (and it has to be summer) - it was a good year. Suffice it to say my chances of Ganymede details in winter in CT is slim to nil. But that's no reason to waft a hand at it.

Pete

Edited by azure1961p (01/30/14 09:59 PM)


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nirvanix
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Re: Plato's challenge new [Re: azure1961p]
      #6342972 - 01/29/14 12:10 PM

"If you doubt, try it. Trust what you see, trust yourself. If not, you're missing out on so much. Often times I trust the view of a faint festoon, and just as often it turns out reasonably close."

Agree absolutely Norme. Too often in our society we overthrow our own mind and senses to place our belief in some "authorities" view. I listen to everyone, follow no one. Observe often, with an open mind, and build up your own ideas about what's out there.

A challenge for me this winter has been hooking up the timing for seeing Plato's craterlets with good enough seeing conditions to do it, but I'll keep trying.


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Re: Plato's challenge new [Re: nirvanix]
      #6343037 - 01/29/14 12:37 PM

Mardi suggested a simple experiment - with a scope and a piece of paper with markings on it - to simply test and replicate observations under varying conditions.

This is what empirical research - and Mythbusters, BTW - is based on.

To believe and trust oneself is healthy on a certain scale, but to be able to replicate and verify an observation is the foundation of knowledge.

So, can you walk the walk - or do you just talk the talk


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Sarkikos
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Re: Plato's challenge new [Re: Mare Nectaris]
      #6343046 - 01/29/14 12:39 PM

"Scientific" data should inform our experience, not dictate it.

Mike


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6343069 - 01/29/14 12:49 PM

Hi Nirv, yea, you know that's a good policy. Listen to everyone, follow no one. Being a moderate, that pretty much sums it up.

But, definitely observe often with an open mind and build up your own ideas of what is out there. There is often debate over theory and real world observing. Truthfully, and maybe ironically, I love "lab like" tests to know what you can see, am a believer in contrast transfer (MTF) despite other's claim it's not real world, and theory in general. It's because in lab like diffraction limited, real world seeing it all makes sense.

Try splitting 7 Tau (~0.75" arc) with a dark space using a 6" scope. When seeing settles, there's a dark space - below the Dawes limit (as reported) but with room to spare for even tighter split. That's what's out there and it seems consistent with theory and what a lab like test /should/ show you. And what's out there is beautifully stunning. It really is amazing what diffraction limited can do.

My Avatar is one of my best Jupiter observations. I still cannot believe this stuff can be seen in a modest 6" scope. But, if you analyze it, there is nothing there that theoretically cannot be seen. Note the absence of white oval 7, my infallible whatever just didn't allow me to imagine it was there - even though I know it is.

Yea, understood about the weather and the timing of Plato's daytime. I missed a chance on the 22nd for the same reason - clouded out.


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Asbytec
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Re: Plato's challenge new [Re: Asbytec]
      #6343101 - 01/29/14 01:06 PM

Quote:

...but to be able to replicate and verify an observation is the foundation of knowledge.



Totally agree, and I wait with baited breath for reports on Plato - hopefully with balmy temperatures and sufficiently good seeing and betting folks can observe more than just the big 4.

By the way, Mythbusters is a great show, but they messed up a little on the cabin pressure experiment. Their "test" was static on the ground with a build up of cabin pressure, it did not replicate an aircraft over 400 knots at 35,000 feet. Nothing they showed proves the Hawaiian airline stewardess did not get blown out of the cabin.

Mike's point is also noted. I find theory pretty accurate in so much as I can observe the differences between what is possible and what is probably under less than lab like conditions. There are limits, but what are those limits. Are they black and white or grey? Do they vary among observers? (Sure they do.)

If it's not on the focal plane you will not see it. If it is there, there's a chance you will. So, the question becomes, is it theoretically on the focal plane? Does it transfer enough contrast, color, or resolution for the "eagle eye" to detect? If so, then it can be seen. But, not always.

Quote:

So, can you walk the walk - or do you just talk the talk...



When you walk the walk, folks should be able to follow (contrary to Nirv's advice above. )

If you talk a good story, no one should be able to repeat your observation. Folks have repeated the apparent Io elongation. I am sure more folks can repeat Ganymede when they catch a higher contrast feature in excellent seeing. And I am sure someone will observe "e" in a modest aperture (if nothing more than with the power of my suggestion ). Any wagers?

What amazes me most is how stunning diffraction limited observing really is. Get a little wind blowing across the object, and all bets are off - including the wager on 'e' above.


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Mare Nectaris
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Re: Plato's challenge new [Re: Asbytec]
      #6343117 - 01/29/14 01:11 PM

When I see somebody use quotation marks around the word science, that pretty much wraps the thing up for me.

To me that means - you just talk the talk


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Re: Plato's challenge new [Re: Mare Nectaris]
      #6343127 - 01/29/14 01:16 PM Attachment (15 downloads)

Well, there's no convincing you then. Shame. You are missing out held back by your own perceived limits.

If you believe you cannot see bright craters on Ganymede, then you probably won't even bother trying and trying again until, finally one good night, you would see them - and know you saw them, and get reports form others who have seen them. And seeing them probably doesn't violate any theory so you can feel safe about seeing them and amaze yourself as the world opens up before you.

Same is true with Plato.

I guarantee you I most assuredly walk the walk, I just wish you could tread up that way a little and see for yourself. Jove in a 6", yes or no? Hint: the answer is yes. There is nothing on there that cannot be on the focal plane. Ask me how I know that is the case. (It did not require a field test, just some good old fashioned observing when conditions are favorable.)

Edited by Asbytec (01/29/14 01:39 PM)


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Sarkikos
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Re: Plato's challenge new [Re: Mare Nectaris]
      #6343166 - 01/29/14 01:39 PM

Quote:

When I see somebody use quotation marks around the word science, that pretty much wraps the thing up for me.

To me that means - you just talk the talk




Who used the word "science" in this thread? No one, until you used it yourself in your post.

I used the word "scientific" in my post. I put the word "scientific" in quotes to signify that not all data deemed scientific necessarily agrees with observed reality in the field. There might be variables at work in the field that are not taken into account on the test bench.

Mike


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Sarkikos
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Re: Plato's challenge new [Re: Asbytec]
      #6343190 - 01/29/14 01:45 PM

Norme,

Great drawing of Jupiter!

The detail you see is similar to what I observe through my 10" f/4.8 Dob on a night of good seeing. I think, though, that through the 10" I can see more detail and mottling in the EB's. There is really not enough time to draw all the detail. I save some time by keeping to a black and white drawing.

I haven't sketched in a while. If I go back to it, I'll probably do sketches of selected areas of the disk, not the entire face.

Mike


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Asbytec
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Re: Plato's challenge new [Re: Sarkikos]
      #6343326 - 01/29/14 03:00 PM

Mike no doubt you observe a lot more molting and finer detail. I'd bet it quickly becomes daunting both theoretically and practically. Heck, its all I can do to keep up with a six inch. Anyway, the point was to illustrate how good seeing and patient, determined observing allows one to "walk the walk." That includes Ganymede, Io, tight doubles at or below Dawes, and Plato craterlets.

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nirvanix
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Re: Plato's challenge new [Re: Mare Nectaris]
      #6343658 - 01/29/14 04:55 PM

Quote:

Mardi suggested a simple experiment - with a scope and a piece of paper with markings on it - to simply test and replicate observations under varying conditions.

This is what empirical research - and Mythbusters, BTW - is based on.

To believe and trust oneself is healthy on a certain scale, but to be able to replicate and verify an observation is the foundation of knowledge.

So, can you walk the walk - or do you just talk the talk




To observe often is empirical research. To observe often and throw out your observations because someone with a certification says you can't see that might be foolhardy.

As far as Mythbusters, please, this is TV's version of empirical science, but is somewhat laughable.


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azure1961p
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Re: Plato's challenge new [Re: nirvanix]
      #6344276 - 01/29/14 11:05 PM

+1 Nirv.

The test thing isn't this wonderful truth detector at all if you've ever tried resolution tests at a hundred yards (or more). If its at night or just before dawn or prior to sun warming the ground its doable. Outside of that its horrendous in a way I hope I never see skyward. That's not why its not such a fine ideal to hold up as some kind of benchmark test . Simply put, if you don't want to believe the observers telescopic work you can just as easily dismiss the test results as biased, edited, omitted.

I personally can't think of a reason in hell for the test if its a personal insight on ones own capabilities. Excuse me but that's what the heavens are for. The only delusional aspect here is the notion that such a test would sway anyone's opinion on wether or not you actually saw anything.

I saw Cassinis last summer almost all the way around given the seeing I had. It appeared to stop just prior to limbs edge. LOL - I don't need to start printing lines and fonts to convince myself how much of the division I actually traced.

Pete


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6344362 - 01/29/14 11:56 PM

Quote:

The test thing isn't this wonderful truth detector...



I guess that's the rub. It's nice if you want to learn your limits or what the scope can do. It's interesting. But the sky is a real test in itself. I've seen Cassini almost all the way around, too, just last year. Yes, even in front of the planet. That's no mystery, it's just beautiful and one of the reasons I set up my scope as often as possible. The things we actually do see is the reason we enjoy this hobby.

Lies and exaggerations don't motivate one to set up nightly or crow about the weather. It'll get boring real fast. There's nothing like a sweet view of anything out there, including Plato...and capturing it's craterlets has it's innate rewards. Not the praise from others, but the real feeling of accomplishment you can believe in. That's where it's at.


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Re: Plato's challenge new [Re: Asbytec]
      #6344493 - 01/30/14 02:49 AM

Your target is a 12point sized disc with grayed out "detail" spots viewed telescopically at a distance of 100 yards at 60X (which roughly equates to the apparent diameter of a 1.2" object at 50x/inch in a 6" scope.) See "detail" in *that* with your 6" reflector. Good luck. (as a target shooter with a good deal of experience looking through spotting scopes at 100yard targets I have a pretty good idea what a "challenge" this would be...)

During the hundreds of sessions I have observed the moon telescopically over the most recent decade, one thing i always do is assess the resolution limit. A lunar craterlet is the highest inherent contrast non-stellar object in the sky. To resolve it into shadow and highlight is of the simplest, grossest order of "detail". The maximum resolution I have ever been able to make out, as a craterlet, is one of about 1.7km --which equates to the diffraction limit of the 6" refractor I was using at the time and was done at seeing which equaled or exceeded the diffraction limit of that scope. (when i had my observatory, standard observing equipment included a hardbound copy of LOPAM, a steel 1/64th inch ruler and a magnifying loupe.) I haven't been able to beat that with an 8" sct (which i have owned and observed with since '08). The optics in the latter scope are noticeably softer than the refractor, understandably, but it is still fun to use.

Now based on this, observing a small object like Ganymede at a crescent phase, as some shape other than a disc, is probably possible. However, seeing gross surface detail *within* a disc that size, which is necessarily of several magnitudes of contrast -less- than a lunar craterlet, IMO, is seeing nothing but diffraction effects animated by seeing and the observer's imagination. If you knew _anything_ about contrast response of the eye you would know this is self-evident...as the resolution threshold of the craterlet requires nearly 100% innate contrast which, when translated by the telescopes optics, is reduced to the eye's contrast threshold, which is around 10%. So *less* innate contrast than a lunar craterlet would be well beneath that threshold--which, BTW can be (and has been ad nauseum) empirically tested (see http://neurovision.berkeley.edu/Demonstrations/VSOC/vsoc/vsoc_main.html) This is all about as "theoretical" in optics as evolution is in biology.

Now, azure1961p, if you are so desirous of "experience", you might listen to David...if anyone here has that, he does. And he has already given you his considered opinion. Also, i would observe that anyone who *attempts* to argue using appeals to (self)authority and juvenile & insinuative ad hominem attacks is going to be taken seriously by *no* one who actually possesses "observational acumen or experience".

I'd also observe that "trusting what you see" is advice worthy of Percival Lowell. And ultimately similarly embarrassing.


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Asbytec
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Re: Plato's challenge new [Re: photonovore]
      #6344526 - 01/30/14 04:13 AM

Mardi, it sounds like we're in general agreement on lunar crater resolution. I, too, have seen down to about the diffraction limit. According to David's figures, 'e' is about 1.7Km and it even begins with something less than 100% contrast at that spacial frequency.

Ganymede is a disc, but it is not a diffraction (spurious) disc in a 6" aperture. It is more of a hybrid between a point source, with faint and diffuse diffraction rings, and an extended object. I am fairly well familiar with random diffraction effects across a small disc like surface. What I saw was far more stable or fixed and became impossible with any amount of seeing. Seeing induced and diffraction effects become much more random and any such 'fixed' sighting becomes much more uncertain. Even in the best of times, it is a dancing point of light that generally hugs the limb in exactly the place it should be.

I do not know the science of such objects, but suspect it behaves something like a bright, equal, close binary system. There is a brightness gradient across Ganymede that may be seen as long as the stable of fixed feature reflects enough light similar to a bright, close companion star. It may not be true resolution in the sense high contrast is required at such high spacial frequencies to separate two points with a dark space, but the feature can be seen regardless, as a gradient across the disc.

You can certainly resolve bright double separated by 100% contrast at the angular diameter of Ganymede. And you can resolve a dark crater floor at higher contrast at about half that angular diameter. It certainly seems possible to resolve a brighter 'spot' on a hybrid object like Ganymede and between point source and a crater half the diameter of Ganymede.

There is no greater resolution in terms of aperture, but at 60x per inch I suspect Ganymede's detain is more easily seen. It's probably the same effect as really magnifying a planetary nebula.

As for Io, I will let Pickering and other observers who "most assuredly" - their words - speak to the issue. One trusted observer noted elongation (even stopped down to 6" clear aperture) with enough accuracy to determine a PA (IIRC that was done at larger aperture.)

Edited by Asbytec (01/30/14 05:41 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6344553 - 01/30/14 05:25 AM

Thought experiment:

We can obviously resolve Sirius from the black of space. Given some artificial and natural lighting, it's not 100% contrast but well more than enough contrast remains to allow Sirius to be seen very easily.

Now, drag Sirius's bright spurious disc and superimpose it over Plato's floor? Think you can see it? Certainly. In effect you are seeing a bright enough point source on an extended object. In fact, you can probably crank down the luminosity of Sirius by quite a bit and still detect it. It no longer has the close to 100% contrast it had against the black of space, but enough contrast remains transferred to the focal plane at some point so that it can be barely seen.

Now, drag Sirius's fully bright spurious disc over Ganymede. Think you could see Sirius? Certainly. In fact it will probably swamp Ganymede's ~5th magnitude surface brightness. Contrast will not be 100% (even at this spacial frequency, if such a concept applies) but there is obviously enough contrast transferred to observe it's brighter spurious disc. In fact, you can again tone down Sirius's brilliance to something much less that 100% contrast until it's just visible against Ganymede. That would resemble the view in a 6" aperture at much less than 100% starting contrast but maybe about 5% at least final contrast.

Bottom line is, you can resolve point sources on extended objects as long as the contrast difference remaining on the focal plane is sufficient for the eye to detect it. Raleigh and spacial frequency may not even apply as long as the disc is an extended object - a hybrid form of resolution that is neither strictly two point sources or an extended object, but a little of both. The result seems to be a gradient detectable by the human eye.

You do not need to be eagle eyed to observe it as long as the feature is bright enough. Ganymede's craters are point sources and are, apparently, just bright enough to be seen much like Sirius would be against Ganymede's disc.

This relates directly to observing Europa at various distances from Jupiter's limb. It can be seen where contrast is at least high enough. There is never 100% contrast needed viewing a point source against an extended object background. So, not sure spacial frequency means anything as it might with a tiny crater floor.


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Re: Plato's challenge new [Re: Asbytec]
      #6345241 - 01/30/14 02:00 PM

Asbytec wrote:

Quote:

We can obviously resolve Sirius from the black of space.




No, you do not "resolve" Sirius. You only can detect the light from Sirius which is gathered by the telescope and focused to a point where the photons from that star interfere and create the diffraction pattern. "Resolving" means separating one detail, object, or point of light from another similar detail, object, or point of light. "Resolving" Sirius would mean actually seeing the true disk of that star instead of its spurious disk. Sirius is only 0.00563 arc seconds across, and the resolution of that disk is beyond most single-aperture Earth-based telescopes (would require something around a 20.6 meter aperture to begin to resolve as a true disk).

Quote:

Bottom line is, you can resolve point sources on extended objects as long as the contrast difference remaining on the focal plane is sufficient for the eye to detect it.




No, you cannot. It is a matter of size, and here, unless the detail separation is comparable to or larger than the size of the diffraction disk for the given aperture, it will not be visible as detail. The size of the disk of Ganymede is simply too close to the diameter of the diffraction disk of a 5.9 inch aperture to allow any significant *surface* detail on that moon to be visible. The actual contrast of the brighter impact spots on Ganymede is far lower than what you often see in images of that moon and would be totally swamped by the diffraction effects of such a limited aperture. Any detail that you might believe you are seeing is spurious and not real. This applies to the craterlets in Plato as well. Indeed, due to diffraction, most craterlets would probably need to be slightly larger in angular size than a telescope's resolution limit in order to appear as significant detail, since they are more complex in their structure than just a simple pair of adjacent points of light like stars. I have observed the moons of Jupiter and have seen no detail on them in apertures smaller than nine inches. Indeed, when detail was visible on Ganymede, it was of the *darker* variety and still was not all that prominent even in apertures 1.5 to 2 times that size. I still have significant doubts about a 5.9 inch being able to resolve craterlets significantly less than about 2 km wide on the moon. If you wish to continue the discussion on Ganymede, it might be better to start a new thread about that in the solar system forum and not here, as this is supposed to be "lunar territory". Clear skies to you.


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Asbytec
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Re: Plato's challenge new [Re: David Knisely]
      #6346104 - 01/30/14 09:45 PM

Quote:

The size of the disk of Ganymede is simply too close to the diameter of the diffraction disk of a 5.9 inch aperture to allow any significant *surface* detail on that moon to be visible.




Ganymede is nearly the angular diameter of an Airy disc, it is therefore NOT a point source. Osiris is a point source. An 8" can resolve it in an image, so it's probably not a resolution problem. It's a contrast problem, which image processing can enhance, and not an extended object on extended object problem like a lunar crater. It is similar to a lunar speck while darker features are much more elusive.

Yes, this requires a new thread, maybe I will start one.

Quote:

Indeed, due to diffraction, most craterlets would probably need to be slightly larger in angular size than a telescope's resolution limit in order to appear as significant detail, since they are more complex in their structure than just a simple pair of adjacent points of light like stars.



Totally agreed. But what can I tell you other than 'e' just sat there in the FOV as a small, faint shimmering dark spot laying on Plato's floor in crater form. That speaks not to the size of the crater at that lunar distance but to the resolution limit that might apply with aperture. It's size was large enough to be seen implying resolution near Raleigh - which is only one of many resolution limits.

So which one of them applies, which resolution criteria must a feature be somewhat larger than? Dawes? Or Raleigh modified by obstruction diffraction effects? I suspect the latter, in this case 'e' would be larger than Raleigh criteria modified by an obstruction. (Again, this seems to be science and theory observed empirically.)

It seems, thus far, Raleigh applies despite the complexity of dark circular features against a surrounding brighter background with the contrast between them somewhat reduced from 100% due to the albedo on Plato's floor. And the craterlet's floor might not be totally black, as well, further reducing contrast.

So, if something this small can be discerned at less than 100% contrast, this tells me an aperture can push even smaller elsewhere on the moon where contrast might be even higher. I cannot say that I have observed anything smaller given the measurement errors involved, but the possibility is there given favorable conditions.

I am hoping someone will take and pass the Plato challenge in excellent conditions and show this to be the case.

Anyway, it's a great discussion.


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Re: Plato's challenge new [Re: Asbytec]
      #6346495 - 01/31/14 03:33 AM

Asbytek wrote:

Quote:

Ganymede is nearly the angular diameter of an Airy disc, it is therefore NOT a point source.




I never said it was a point source! Its size, however, is very close to that of the spurious disk of a star. Diffraction effects on that scale will completely obliterate any small-scale detail like the albedo features on Ganymede. There is simply no way to get around that. All one can say for certain is that a 5.9 inch will resolve the disk of Ganymede, showing it to be slightly larger than the diffraction disk of a similar magnitude star, but that is all that can be said about it.

Quote:

So which one of them applies, which resolution criteria must a feature be somewhat larger than? Dawes? Or Raleigh modified by obstruction diffraction effects? I suspect the latter, in this case 'e' would be larger than Raleigh criteria modified by an obstruction. (Again, this seems to be science and theory observed empirically.)




Again, Dawes limit cannot be applied here as it only applies to double stars. The Rayleigh resolution limit also is for point sources, although it can serve as a "rule of thumb" guide in the case for certain detail. For a 5.9 inch 31% obstruction at 5500 angstroms, it would be 0.834 arc seconds, and at the moon's mean distance of 384,400 km, that would represent a linear distance of about 1.55 kilometers. Again, due to the way that extended objects have a more complex diffraction structure than just two adjacent (and overlapping) diffraction patterns, the actual minimum diameter of a craterlet visible as the true pit it is in a 5.9 inch would have to be somewhat larger than this in order to be seen as anything more than a blurry barely detectable "something". I might suggest doing some research on other craters of known diameter. One that could be a good target would be Linne, which is about 2.22 km in diameter and has both a well raised rim and a small bright ejecta halo. Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6346530 - 01/31/14 05:41 AM

David, yea you never said it was a point, but you said it was the size of the Airy disc and that can get confusing. I was clarifying and emphasizing because it likely means different rules apply to Osiris on Ganymede than strict Raleigh or Dawes. It behaves more like a transit of Europa easily seen on the limb and gradually fading due to contrast falling off. Osiris seems to be relatively bright enough - just so - to be detected as a speck. Darker features are much more elusive, maybe a 9" is required to really see them as something other than a soft limb darkening.

I trust your calculation of 1.55km at the lunar mean distance based on your calculation of an obstructed Airy disc diameter. And also agree that a crater somewhat larger than the pure Raleigh limit (0.83" arc) might be required due to less than 100% object contrast resulting in less contrast transferred to the focal plane. That fits with theory and my own calculations. In my view that also, in turn, fits with an empirical observation of 'e' with a diameter of 1.73km despite - and maybe resulting from - it's contrast environment. It's these types of observations tending to agree with theory that makes me a believer theoretical diffraction limited performance can indeed be observed.

So, to say Raleigh might be a limiting rule of thumb makes sense, if we define Raleigh as 1.22 Lambda/D. A 6" obstructed aperture can probably resolve down to it (being larger that 0.83" arc resolution at a given distance), an unobstructed 6" aperture might not requiring something larger than 0.92" arc. Without grinding through the math, again, I think this small difference in Airy disc radius implies about 0.1 mile resolution advantage for an obstructed aperture and consistent with theory.

The interesting thing about 'e' is it seems to push resolution closer to an obstructed Raleigh limit suggesting resolution is somewhere between 1.73 and 1.55km at the lunar mean distance or a bit closer toward 0.83" arc at any distance. Craterlet 'e' is still larger than obstructed Airy disc diameter, and should be resolved as expected.

Craterlet 'e' was indeed a blurry something. It was a dark shimmering spot on Plato's floor that swayed even in very good seeing. If memory serves it had no distinct lip or other more crater-like features as Linne or larger craters with a wealth of detail. Craterlet 'e' was devoid of any of that. Nor did it suffer any diffraction effects to blur it's image into an indistinct mess or a speck.

So, I interpreted the tiny shimmering dark patch as it's crater floor hence determined 'e' to be resolved in crater form. I watched it shimmering there for several minutes, plain as day.

Anyway, it's a great discussion. I just hope others are following along as we explore the complex subject of extended object resolution, empirically and in theory.


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azure1961p
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Re: Plato's challenge new [Re: David Knisely]
      #6346721 - 01/31/14 08:57 AM

Quote:

Asbytek wrote:

Quote:

Ganymede is nearly the angular diameter of an Airy disc, it is therefore NOT a point source.




I never said it was a point source! Its size, however, is very close to that of the spurious disk of a star. Diffraction effects on that scale will completely obliterate any small-scale detail like the albedo features on Ganymede. There is simply no way to get around that. All one can say for certain is that a 5.9 inch will resolve the disk of Ganymede, showing it to be slightly larger than the diffraction disk of a similar magnitude star, but that is all that can be said about it.
.




This doesnt appear to be so though David. There's more going on here than the formation of a poker faced Ganymede masked by its own diffraction effects of modest aperture. The case for my disagreement harkens back to Pickering seeing Io as egg shaped (which they now image frequently). If diffraction effects truly masked any surface details Io through Pickerings 5" would have been averaged out as a disc without any deviation from a circle. I've not dont the 5" Io thing but I saw it through my 8" - its difficult but easier than Ganymedes details. Io I can see egg-like in good Pickering 6 while the latter is 9+. It may truly be Ill never see a shading again till its a summer object but that's my finds anyway. I don't think diffraction obliterates in these cases but is an aggravating factor.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6347027 - 01/31/14 11:35 AM

You seem to refer frequently to William Henry Pickering and observations on Io. - Please read "The Story of Jupiter's Egg Moons" in Sky & Telescope, January 2004, pp. 114-120, written By Thomas Dobbins and William Sheehan.

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azure1961p
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Re: Plato's challenge new [Re: Mare Nectaris]
      #6347940 - 01/31/14 07:44 PM

Yes Im very familiar with it. What it underscores is the fact that a small medium aperture is capable of *resolving* detail on a disc virtually 1" across. The egg shape is a hamfisted diffraction effect of the true nature of the darker polar regions versus the brighter equatorial region. If diffraction effects obliterate detail at this level no such egg shape would be evident and the contrasts would be averaged out in a poker face circle.


Where Pickering derails his own efforts is assuming he'd hit some higher truth about all the moons and so in turn hallucinated all moons as being egg shape!!! Its a fine article by two of the best out there. Or one of the two best.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6348138 - 01/31/14 09:52 PM

Retracing Pickering's historical observation was a real treat. I felt honored. As a result, the observation was one of the most exciting to date. I guess that's the point of these difficult observations, including the Plato challenge. They are rewarding and beautiful.

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Re: Plato's challenge new [Re: Asbytec]
      #6348744 - 02/01/14 09:41 AM

The authors of the article simply come to the conclusion that Pickering was a victim of refractor tube currents - and of not being able to let go of his fixation based on a mere illusion.

From the article: ”William did work hard at his observing. At Arequipa he used the Boyden Telescope, a 13-inch refractor made by the renowned Alvan Clark firm, to measure the diameters of the Galilean satellites using a filar micrometer. These were delicate observations – Ganymede, the largest of the Galilean satellites, never appears larger than 1.6 arcseconds across, and the smallest Europa, is a paltry 1.0 arcseconds wide. That’s just a little larger than the Airy disk of the diffraction pattern produced by a point source in a 13-inch telescope. Pickering’s customary magnification was 700x, with occasional resource of power as high as 1,305x.” (p. 115).

When a famous astronomer Edward Emerson Barnard was able to confirm Io being round – and observe a light horizontal pattern on Io’s surface – using the 36-inch Lick observatory Clark refractor, Pickering did not believe but responded (p. 118): ”a phenomenon which appeared to us so obvious at Arequipa has not been confirmed with the 36-inch telescope.” And the article continues (p. 118): ”Pickering lamely countered that a large telescope like the Lick refractor ”gives far too much light to enable one to distinguish the shapes of the satellites clearly.” He encouraged amateurs to verify his observations, claming that under good conditions the satellite’s distorted disks were ”readily visible with a 5-inch telescope, and can be seen with one of 4-inches aperture.” During 1894 Pickering and Douglass continued their studies of the Galilean satellites at Lowell observatory in Flagstaff, Arizona. … It’s hard not to chuckle when contemplating the long hours they spent at the eypiece mistaking activity for accomplishment.”

The authors of the article call Pickering’s claims on the shape of Jovian moons ”one of the strangest misadventures in the history of observational astronomy” (p. 114). – They cite Joseph Ashbrook writing on Sky & Telescope December 1963: ”How could it happen that a competent astronomer spent decades in such a blind alley? There is no easy answer. I suspect that some actual phenomenon – for example, deformations of disk outlined by seeing – was habitually interpreted as real, and that Pickering trained his fellow observers to interpret as he did.” (p. 116).

The authors also cite (p. 120) the ”Adjustment and Testing of Telescope Objectives” (published in 1891) by H. Dennis Taylor: ”The effect of cooling upon the tube [of a refractor] and its enclosed air is to cause peculiar slow flickerings of the image, and sometimes to produce a pronunced astigmatic effect, owing to the gathering of the warmer air towards the upper side of the tube… All these effects seem to be more noticeable in the case of tubes which are only just large enough to pass all the light from the objective; a tube with plenty of room in it certainly tends to better images.”

And the authors continue (p. 120): ”Is it any coincidence that for three decades Pickering’s observations of the Galilean satellites were all made with refractors from the firm of Alvan Clark and Sons, all of which had close-fitting tubes? Pickering’s 12-inch Newtonian reflector, which had an octagonal wooden tube ventilated with an electric fan, newer showed Jupiter’s moons as ellipses. Pickering even cited this failure as an example of the refractor’s inferior definition!”

The authors also refer to their own experince: ”On five nights in August 1995, we were able to eamine the Galilean satellites through the 36-inch Lick refractor… on two evenings shortly after sunset the satellites appeared distinctly elliptical at magnifications of 568 x and 1,176 x. Altough they undulated due to atmospheric turbulence, the major axes of these ellipses remained roughly aligned with the vertical diameter of the telescope’s tube. We suspect that a similar view made a profound impression on Pickering on that fateful evening of October 9, 1892. His judgement was so impaired that when he recalled the numerous occasions over the years when he saw the moons as round when his ephemerides predicted ellipses, he dismissed the circular appearances as ”merely a subjective phenomenon”. It is especially ironic that Pickering fell victim to these illusions since he was keenly aware of the effects of tube currents.” (p. 120).


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Re: Plato's challenge new [Re: Mare Nectaris]
      #6348756 - 02/01/14 09:56 AM

Here is an interesting blurb on Pickering from the Moon Wiki:

Quote:

Despite the fact that W.H.Pickering's "odd" lunar observations and descriptions of so-called "insect swarms" at and near craters such as Eratosthenes were (and are) seen as some kind of "madman's disease", we should keep in mind that newly discovered terrestrial lifeforms (extremophiles) are capable of living in very hostile environment, such as space and direct cosmic radiation! If cometary nuclei or small asteroids contain possible quantities of some sort of interplanetary extremophiles, then...




Lunar Observers

Pickering's career appears to have been a series of inspired hits and idiosyncratic misses.

William Henry Pickering

Mike


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Re: Plato's challenge new [Re: Mare Nectaris]
      #6348816 - 02/01/14 10:33 AM

Well, there ya go. When you cite authoritative works or respected observers, then all claims of lesser known or observers with less credentials must be discounted as tube currents. I feel Pickering's pain and believed in his work even before I knew about it. So he was unlikely to convince me prior to observing.

In fact, I only hoped to observe its apparent elongation against the backdrop of Jupiter's clouds as images capture regularly. While waiting for Io to transit one night, with Europa in the FOV, Io began to hint of elongation in excellent seeing at well above 50x per inch.

I don't mind being a pariah if being one encourages others to push deeper into observing such things, whether it's Jovian moons or Plato - I know what can be seen and the pariah moniker will wear off. I report what I see, not illusions and certainly not tube currents. Currents do not exist in my well collimated scope at night in the moderate tropical climate with diffraction limited seeing - I check for them often. And it was not tube currents I was seeing "aligned with the scope's vertical axis" or otherwise, especially with Europa in the FOV NOT exhibiting the same behavior. It was Io's "appearance" of elongation, especially when compared to Europa or Ganymede, just as Pickering claimed we could observe in modest apertures.

You can write it off as tube currents or delusions if you want. You can even claim supernatural influences from little green men, I could care less. It's not uncommon for folks to cite references in support of their own skeptical disbelief. It's a lot harder and more exciting to observe it and learn to believe with some form of zeal for exploration. It's easier to disbelieve than to believe. So be it, it's the way of things.

As for Pickering's observation itself, I assert it is a function of diffraction and contrast transfer as the moons are certainly not elliptical as proven in larger apertures (and befuddled Pickering as he was indeed wrong about their shape). They only appear that way in smaller apertures. Larger apertures will show them disc-like with maybe a brighter equator.

"It is especially ironic that Pickering fell victim to these illusions since he was keenly aware of the effects of tube currents.” Ah, poor Pickering, he doesn't know any better. Indeed, nor do I. And we're both being discredited by that very phenomenon that simply does not discount the very real "appearance" of elongation if one cares to take a careful look at the risk of fooling yourself. But, there are those who prefer the safety of common knowledge, while frankly Ganymede and Io should be common knowledge.

So, who is going to observe 'e' and chalk one up for the Gipper?


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Re: Plato's challenge new [Re: Asbytec]
      #6349208 - 02/01/14 01:36 PM


I wish I had the article now.

Io was correctly seen by Pickering as ovular. Its not thermals, its not a selective waft of air distorting that moon only - it appears oval due to diffraction - the brighter wide equatorial zone with dark polar regions causes the round moon to appear ovular due to the smaller aperture not having the resolving power to define the issue at hand.

That Barnard saw it as round is no argument against the fundamental effects of diffraction at play. As I mentioned previously - where Pickering details himself is in viewing elongated moons due to seeing and thinking he had struck a higher truth. This is a text book example where his unsound judgements were at work.

That the poor soul spent years chasing poor seeing is tragic ( I find it hard to chuckle as he was passionate) but that does utterly nothing to sway fact that Io appears oval through apertures similar to his instruments. Here's links to photos showing what can also be seen visually.


http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6334144/page...

Here's a movie of it :
http://www.youtube.com/watch?v=PpEdBplDHxM&feature=youtu.be

Scroll down you'll see - and this is through a 6":
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5548739/page...


What's puzzling here is all you've outlined is the negative in that article completely bypassing even the graphics that spell out how Io could appear this way.

I've even seen an image of oblate Io shot by a 5" apo - and the other moons are perfectly round. If a 5" can image it I certainly can see it through my 8". The 36" results are proof in the pudding that the effects are purely diffraction.

Give it a whirl yourself. You need at least Pickering (ha!)6 or better and something like 250x and up. Europa makes a perfect control in this visual experiment as its clearly apparent roundness serves to help define IOS oblate appearance.

Pete

Edited by azure1961p (02/01/14 01:37 PM)


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Re: Plato's challenge new [Re: azure1961p]
      #6349236 - 02/01/14 01:48 PM

Lastly and to a better place - the following link is where one amateur having seen Io as oblate and questions it has the topic explored and expanded on with lustrations and if course that article. Its worth a read :

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5540082/page...

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6349409 - 02/01/14 03:27 PM

What can I say

P l e a s e *read* the whole article yourself: "The Story of Jupiter's Egg Moons" in Sky & Telescope, January 2004, pp. 114-120, written by Thomas Dobbins and William Sheehan.

Do not merely trust a Wikipedia article, citing only a tiny part of the original text.

In the briefing above, I have *not* only selected critical parts of the article. On the contrary, I was careful in duplicating the main findings of the article, word by word. The article actually is *very* critical and realistic in arguing the case of Pickering observing the shape of Jovian moons.


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Re: Plato's challenge new [Re: Mare Nectaris]
      #6349417 - 02/01/14 03:30 PM

No no no I had the entire article a year ago or so. Must've deleted it - darn it all!!! The whole thing is he went to hell with himself on self suggested prejudgements - a knack of his - and to look at all the moons as a failed observation js to erase the one virtue in his whole endeavor.

I see egg moons more often than not around Jupiter. Even if its fine under Pickering 7 - once I hit 400x alas the trailer eggs smeared by seeing. That's why its my contention such excellent seeing is needed to glean a shading off Ganymede as it usually falls apart just at the point you hit the right magnification.

Timo - give that link a gander by Jason Burry, Ed Moreno weighs in with sone authority there too . Mind you not on Pickerings dreamt errors but his one true call on Io.



Pete

Edited by azure1961p (02/01/14 03:37 PM)


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Re: Plato's challenge new [Re: azure1961p]
      #6350067 - 02/01/14 09:25 PM

The article was available online at the time of Jason's thread, I think we all read it.

It certainly feels as though selective parts of the article were highlighted above to disprove the elongation. It may prove that Io is not elongated and Pickering was mistaken, and it turns out he was. However it doesn't disprove it appeared to be that way to him. Io is not egg shaped, we know that, but it certainly can appear elongated.

Quote:

He encouraged amateurs to verify his observations, claiming that under good conditions the satellite’s distorted disks were ”readily visible with a 5-inch telescope, and can be seen with one of 4-inches aperture."



And this is all I am saying is correct and an exciting observation in itself.

Here's the kicker. If Io's albedo can show elongation, likely due to it's darker poles, it might be said it's brighter equator can be observed. Detail on Io?

Edited by Asbytec (02/02/14 12:10 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6350331 - 02/02/14 12:05 AM

Well if there were no detail to be seen it'd appear like a yellow peachy Europa but as we know that's not he case.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6350360 - 02/02/14 12:23 AM

Yea, the definition of "resolution" comes into play here. Is it resolved? I would think so.

Trying to keep this extended object excursion on topic with Plato, as I think extended object resolution is pertinent in any form, we can probably toss the book out the window and go see what we can see - resolved or otherwise.

Some things may not be resolved per the accepted resolution limits, but they can be observed. Extended object resolution does not follow the rules nor definitions precisely, craterlet resolution (vs speck detection) comes close approximating Raleigh, IME. But even that is complex as David explains.

Plato offers us a chance to test those limits. I've pushed the bar to 'e' in a 150mm aperture quite by a chance sighting of 'e' on a good night. (And I have witnessed first hand Pickering's account of Io and seen features on Ganymede.) Like Pickering, I encourage others to observe these things as well, beginning with Plato, when conditions permit.


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Re: Plato's challenge new [Re: azure1961p]
      #6351332 - 02/02/14 02:13 PM

Quote:

Quote:

Asbytek wrote:

Quote:

Ganymede is nearly the angular diameter of an Airy disc, it is therefore NOT a point source.




I never said it was a point source! Its size, however, is very close to that of the spurious disk of a star. Diffraction effects on that scale will completely obliterate any small-scale detail like the albedo features on Ganymede. There is simply no way to get around that. All one can say for certain is that a 5.9 inch will resolve the disk of Ganymede, showing it to be slightly larger than the diffraction disk of a similar magnitude star, but that is all that can be said about it.
.




This doesnt appear to be so though David. There's more going on here than the formation of a poker faced Ganymede masked by its own diffraction effects of modest aperture. The case for my disagreement harkens back to Pickering seeing Io as egg shaped (which they now image frequently). If diffraction effects truly masked any surface details Io through Pickerings 5" would have been averaged out as a disc without any deviation from a circle. I've not dont the 5" Io thing but I saw it through my 8" - its difficult but easier than Ganymedes details. Io I can see egg-like in good Pickering 6 while the latter is 9+. It may truly be Ill never see a shading again till its a summer object but that's my finds anyway. I don't think diffraction obliterates in these cases but is an aggravating factor.

Pete




Over the past 46+ years since my first view of Io way back in 1967 in my first telescope (3" f/10 Newtonian), it has never appeared as anything other than a dot or a small disk. It never appears out of round, and even in my 14 inch, it just shows its pale dirty yellowish disk. The only time I ever got to see any major detail on that disk was during the Nebraska Star Party using a 30 inch Newtonian at over 500x. Even then there wasn't a lot of detail to see. The polar regions were only very slightly darker (and *not* uniformly so) than the rest of the moon's disk with rather low contrast. Sorry, but elongation of that moon just hasn't been in the cards for me (and Pickering's observations are not worth commenting on, as they clearly represent something other than a true level of detail or resolution). Imaging to support "elongation" also has some problems, as the transiting Io will tend to have adjacent linear detail change the shape of the dot of Io in a way that is not necessarily matched visually. Again, the resolution of the disks of the moons of Jupiter and any detail they might show would be best done on a different forum. Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6351486 - 02/02/14 03:29 PM

Quote:

Over the past 46+ years since my first view of Io way back in 1967 in my first telescope (3" f/10 Newtonian), it has never appeared as anything other than a dot or a small disk. It never appears out of round, and even in my 14 inch, it just shows its pale dirty yellowish disk.



Similar experience here - when Io is seen against a dark sky. I'm pretty sure that irridation has a major effect in reducing the visibility of albedo markings on the tiny disk, with such a large contrast between the bright disk edge and the black sky.

However when Io (or Ganymede) is in transit across Jupiter's face, irridation is far less of an issue & with sufficient aperture (I'd say 8"+) and good, steady seeing conditions, albedo markings may be glimpsed ... but contrast effects against the variable brightness of Jupiter's belts, zones and spots may well be a factor.

I've suspected albedo markings on Ganymede a few times and Io once, with 8" & 11" SCTs, when in transit but not otherwise. Europa is more difficult (smaller size & much more uniform surface) whilst Callisto in transit is dark enough for irradiation from the planet's surface to be a serious handicap. Perhaps Callisto might yield albedo markings when in transit against the limb, but transits of Callisto are relatively rare & opportunities for observing at this phase correspondingly limited.

I think that irradiation effects are at least as much of a factor as diffraction, for observations made with moderate apertures and/or in less than perfect seeing.

This sort of observation is very difficult: I would refer you to the drawings of Jupiter's moons in Webb's "Celestial Objects for Common Telescopes" which show a large variety of near polygonal shapes for the satellites and surface features which again bear little if any relation to the actual features revealed by space probes. Mercury's surface albedo features are a lot easier than those of the Jovian satellites (when not in transit) but the rotation period derived from visual observations was proved to be completely wrong by radar in the 1960s.

Edited by brianb11213 (02/02/14 03:32 PM)


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Re: Plato's challenge new [Re: brianb11213]
      #6351585 - 02/02/14 04:19 PM

Quote:

whilst Callisto in transit is dark enough for irradiation from the planet's surface to be a serious handicap. Perhaps Callisto might yield albedo markings when in transit against the limb, but transits of Callisto are relatively rare & opportunities for observing at this phase correspondingly limited.




http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6294206/page...

Not wanting to contribute to further 'off-topic' here .

Been otherwise detained (again) but have been following things on this thread, and CN in general, and have something to contribute - elsewhere in due course

Regards All.


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Re: Plato's challenge new [Re: David Gray]
      #6351725 - 02/02/14 05:21 PM

I look forward to it Dave.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6352133 - 02/02/14 09:55 PM

I guess the whole point of discussing all these various extended objects is not to be bound by accepted resolution limits as often asserted or interpreted as limits and to get out and see what you can see - without fooling yourself or falling victim to seeing or diffraction effects. That includes Plato as well as Io, Ganymede, or Callisto. (I've not tried to see detail on the latter, it does look very weak requiring some aperture.)

If science is your guide, and it should be, you might find yourself surprised. Using science as a guide probably means understanding the type of detail and where the theoretical limits really are defined. As Mardi wanted to show above with a 'test', any of these objects can be a real test.

To be clear, I am not claiming to have directly seen albedo features on Io - only the appearance of elongation. Depending on how one might interpret resolution, though, it's entirely possible Io's apparent shape is a result of albedo differences and not because it's disc is actually elongated, egg shaped, or anything other than circular - in appearance. And it's repeatable, but folks tend not to believe it because they might be unsure how to interpret what Raleigh, contrast, or diffraction theory say is or is not possible - on paper verses the sky.

Irradiation plays an important role, surely. All I can say with any assiduity is that comparing Io's apparent disc to Europa's there is something 'wrong' with Io's disc. It does not appear round even though it certainly is. Maybe I should not have seen 'e' according to how theory might be applied to lunar resolution, but it was most certainly there.

I don't believe observing 'e' (Io, or Ganymede, or David's observation of Callisto for that matter) violates theory, rather pushes back our interpretation of what theory might suggest is a limit.

We've all seen some discussion on extended object resolution, but I am not aware of a serious mathematical treatment or model explaining it. Theoretically, if contrast must be very high in accordance with spacial frequencies involved, then we should not see Europa transit any part of Jupiter's disc - contrast is just not 100%. Of course it does fade toward the meridian as contrast falls off, but what are the limits of contrast?

Viewing a speck on Plato's floor is probably a single point source form of resolution against a bright background much like Osiris is on Ganymede. If brighter specks can be seen on the moon, then why is it not possible to barely see a fainter speck on Ganymede? Why would not Io erupt into a series of diffraction patterns when its disc is larger than an optical point (1/4 Airy disc diameter?)

It's quite possible Io's PSF can be elongated along the axis of it's brighter equator markings and compressed slightly along it's central meridian with the poles at either end in much the same way a dimmer star is slightly smaller than a brighter one - irradiation or diffraction causing this appearance. And 'e' may well follow the rule of thumb for Raleigh depending on how one calculates that limit (obstructed vs unobstructed.)

Again, I am not convinced theory is in error, but rather our interpretation of what theory might say seems to be somewhat restrictive. Diffraction limited seeing is truly beautiful in that theory can be observed rather than discussed.


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Re: Plato's challenge new [Re: David Gray]
      #6352160 - 02/02/14 10:12 PM

Quote:

Been otherwise detained (again) but have been following things on this thread, and CN in general, and have something to contribute - elsewhere in due course...



I look forward to it as well, David. Maybe we need a separate thread, but I don't mind discussing each aspect of extended object resolution while we wait for observations of Plato to roll in. It all applies, really.


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Re: Plato's challenge new [Re: Asbytec]
      #6353142 - 02/03/14 12:15 PM

Keeping this thread on Plato is a good idea.

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Asbytec
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Re: Plato's challenge new [Re: star drop]
      #6354487 - 02/03/14 10:19 PM

Plato should be visible in a few days, I'm hoping the weather will allow someone to report on it. I plan to observe it again. Craterlet 'e' is of particular interest, but may be better seen during Plato's sunset a few weeks from now.

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Re: Plato's challenge new [Re: Asbytec]
      #6363440 - 02/08/14 07:12 AM

Okay, first glance at Plato on 8 Feb 1200UT just emerged from the terminator. IMO, Plato's floor is still too dark with glancing sunlight.

I could see the big 4 as faint light arcs and maybe, just maybe darker pits. However, when I say the big 4, I mean the 'c' and 'd' were kind of seen together and not resolved individually.

Craterlet 'w' was a solid dark spot against the wall. Craterlet 'e' was difficult, but it showed itself a few times as a faint, fleeting light arc like the big 4.

It's too early, need another day (per edosaurusrex post), I think to see them better. But the seeing was good and it was clear...was clear, so I took a chance on it.


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Re: Plato's challenge new [Re: Asbytec]
      #6363451 - 02/08/14 07:26 AM

Good work Norme. I had a quick peek at Plato last night through the clouds. Definitely the crater floor was too dark to make an attempt. Wishing us both good skies tonight.

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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6363454 - 02/08/14 07:29 AM

Thanks, Nirv.

Gotta check the skies. Not a cloud on weather radar, but it certainly closed in regardless...low stuff.


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Re: Plato's challenge new [Re: Asbytec]
      #6365591 - 02/09/14 08:41 AM

Okay, add 'g' to the list of craters in crater form! Serious as I can be, confirmed with it showing nice floor and a crescent rim brightening twice in a half hour of viewing. No question about it, full on crater form with a dark pit and a sunlit crescent confirmed twice. (Edit: and again a third time at 1330UT while sketching.)

I also spotted 'h' for sure and I suspect 'i' and only /suspect/ having glimpsed each with a dark pit once or twice. Actually I did see a dark spot there only fleetingly, so it is way too uncertain to call with any confidence. These two were mostly brighter specks than rolled into and out of view with the relatively good seeing.

I held 'e' for long periods of time in crater form. No question about it, no tomfoolery. Plain as day. It was somewhat dimmer with a fainter floor and dimmer crescent shaped sunlit inner pit than the big four. I did not notice a thinner crescent outer rim. The thing about 'e' is it sits kind of in a darker albedo area, but seems to have a brighter albedo streak pushing across it.

The big four were in full crater form with 'A' showing not only a dark pit, but also a crescent shaped sunlit inner pit and a bright outer rim. Craterlet 'B' same description. Craterlets 'C' and 'D' were well resolved with a nice dark pit and sunlit crescent interior as well. However, their sunlit outer rim was less prominent.

Feb 9th at 1100UT, seeing was excellent (8/10 or better mostly.) Transparency was descent. I was at 320x with 6mm TMB II. The moon's distance is about 400,000Km (402,678 according the JPL sim and 398,086 according to Virtual moon Atlas.)

Man, I could not be happier to have such great nights to be thankful for. On such nights, if you'll forgive the religious reference, I just have to give a prayer of thanks. Serious, just as we do on Thanksgiving. WOW

Edited by Asbytec (02/09/14 08:42 AM)


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6365863 - 02/09/14 11:47 AM

Hey, congrats Norme! Have to admit I'm a little jealous

What is your total Plato craterlet count? Are you at eight? That's a fine accomplishment for a 6 inch scope.

I was out last night but my sky was as lumpy as oatmeal. Looked over to Plato and the alpine valley, and did spot the three biggest 'lets', but no chance for gravy and glory.


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6366040 - 02/09/14 12:56 PM

I am at 7 in crater form: A through D, e, and w makes 6 then g tonight makes 7. I think you are, too, yea? Specks were pretty hard to see tonight. I am not calling 'h' or 'i' as crater form sightings, wish I could.

Yea, Nirv, seeing is totally everything. Please excuse me admitting I just love that 6" Mak under nice skies. It never ceases to amaze. Never. I'm simply awestruck.

Were you able to observe this evening?


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Re: Plato's challenge new [Re: Asbytec]
      #6366177 - 02/09/14 01:56 PM

Hi Norme,

Was your first sighting of "g" at 1100UT? If not, tell me when it was so I can update the prediction table.

Thanks,

Ed


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Re: Plato's challenge new [Re: edosaurusrex]
      #6366687 - 02/09/14 05:37 PM

Been following this thread with interest, last month I had cloudy skies, and so far this month it has been one storm after another.
However, tonight is clear, and while the seeing conditions are not the best I had a go with my 6 inch f/15 refractor at 180x power.
A,B,C, and D seen as crater form. G was glimpsed in better seeing moments as a bright spot. E was observed, but was difficult,
appearing as a bright spot during moments of better seeing..


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6366884 - 02/09/14 06:54 PM

Quote:

I am at 7 in crater form: A through D, e, and w makes 6 then g tonight makes 7. I think you are, too, yea? Specks were pretty hard to see tonight. I am not calling 'h' or 'i' as crater form sightings, wish I could.

Yea, Nirv, seeing is totally everything. Please excuse me admitting I just love that 6" Mak under nice skies. It never ceases to amaze. Never. I'm simply awestruck.

Were you able to observe this evening?




I've got clear skies tonight so will be trying again. Last year I got 7 plus an albedo feature.

You should enjoy and be proud of your Mak! Did you try for the alpine rille? I will look for it tonight also.


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Asbytec
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Re: Plato's challenge new [Re: edosaurusrex]
      #6367166 - 02/09/14 08:54 PM

Quote:

Hi Norme,

Was your first sighting of "g" at 1100UT? If not, tell me when it was so I can update the prediction table.

Thanks,

Ed




Hi Ed, do you need accurate time for that? I began observing at 1110UT through 1145UT, my first sightings were between those times. Both were within a few minutes of each other, I would estimate about halfway though pretty near 1125UT.

Having observed on the 8th, the big 4 were more difficult as faint arcs seen against Plato's darker floor. The improvement tonight was spot on according to your predictions earlier in this thread.

Quote:

...and while the seeing conditions are not the best I had a go with my 6 inch f/15 refractor at 180x power.
A,B,C, and D seen as crater form. G was glimpsed in better seeing moments as a bright spot. E was observed, but was difficult,appearing as a bright spot during moments of better seeing.




Rich, I bet you could have nailed e if seeing settled into a perfect moment. In such seeing, I was able to hold it for long periods, I am fully confident you would have done likewise.

I got the feeling it was slightly elongated, but not sure why. Maybe it is, maybe they all are to some degree due to the angle we view Plato, but it was just more obvious with e than the others. There were some brighter spots or albedo nearby toward Plato's center and toward w.

I was literally stunned to notice g, however. It did roll in and out most of the time as a faint white something. I would not call it a bright speck, just kind of a faint indistinct faint and fleeting smudge. About twice as I noticed it and once again a bit later (taking a break from sketching as seeing had improved again), it just settled into a very tiny, dark gray shadow with a lit rim crescent for a third time.

What's interesting is h is apparently two craters or at least an elongated one. In sum, but maybe not individually, it is much larger than e or g, yet I never managed to resolve it. It was the same faint and fleeting white smudge and maybe once viewed as a dark spot. I (I believe) was the same.

I am wondering if 'f' can be seen, I didn't notice it. But then again I didn't think to look up there that close to the wall with shadow cast along the floor. It may have been in shadow, dunno. I do not remember seeing the east wall pit.


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6367226 - 02/09/14 09:33 PM

Quote:

Thanks Norme. I've seen A-E and g,h. Will have to try for i,j. There is no l,n, o ?




Ah, okay, Nirv, reading back I see you nailed g and h. You don't list w, which is pretty easy when the west wall is not in shadow. You can pick that one nicely for a total of 8, no problem.

Again, h is interesting in that combined it is fairly large. Yet I could not resolve it as a combined or elongated form. Maybe just gonna have to try harder next time.

Good luck with the smaller ones, I'm pulling for you. You have a nice ten inch aperture, right? It'll be interesting to see if conditions will allow it, if so I'm betting you can.


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Re: Plato's challenge new [Re: Asbytec]
      #6367230 - 02/09/14 09:40 PM

At this point can you provide a notated image of Plato Norme? I'm very happy for every one here .


Pete


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6367290 - 02/09/14 10:14 PM Attachment (13 downloads)

Sure, was thinking the same. Something like this.

The one in the north was kind of hard to place, it was about there. The spot just above 'e', not sure what that was. But, it was persistent. Maybe albedo? It was too close to 'e' to be 'p.' I do not think I saw 'l.'

Over by 'n' was a small string of albedo or specks not well defined, one of them was likely 'n', that bright spot was in the right place.



Edited by Asbytec (02/09/14 10:32 PM)


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6367380 - 02/09/14 11:07 PM

Well how do all? I spent another two hours out this evening in -25C, but it was fine until the wind picked up and drove me inside. My nose felt like it was being bit off.

The first half on my time was spent watching a lovely transit on Jupiter, but then turned attention to Plato mostly, and a few minutes on the Alpine Rille, with a brief stop prior to my moon landing to split out the e and f from the trap. It was straight forward task.

My sky was cycling with short (1-3 secs) bursts of very good seeing between the continuing bubbles. I'm starting to be bold now as the seeing improves and going straight for the gusto of high mags. Started out on Jove with 400x and stayed at that power for the duration of the night.

I was able to spot sections of the Alpine Rille, but never the whole length in one go. As for Plato, A-E, W easy, and I would say that during a few really good cycles I noted g and h as more than just albedo features - they looked structural. Try as I might couldn't make out much for k,p,q,m,i,j. Maybe a speckle for k and m. Perhaps the illumination isn't quite right, but I'm too cold and stiff to go back out! Kind regards and happy hunting.


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Re: Plato's challenge new [Re: Asbytec]
      #6367396 - 02/09/14 11:15 PM

Okay, here's what I know to be true having seen g with a crater pit and a faint crescent. Apparently g is about 1.5km in diameter and the moon's distance is about 400,000km or close enough for both measurements.

Using the small angle formula (which I think is an approximation itself) then g subtends an angle of ~0.77" arc. Yes, that's the Dawes limit for a 150mm aperture. But, here's the kicker, my aperture is obstructed and that has diffraction effects altering the diameter of the Airy disc by an approximate factor of 1 - co^2. Actual Raleigh type resolution falls from 138.4/150 = 0.92" arc to about 0.83" arc. The Dawes equivalent falls to closer to 0.69" arc.

So, seeing g and maybe f in an obstructed aperture is actually is not that mysterious of an observation so long as seeing is diffraction limited at 8/10 Pickering or better. It falls within what would be the Raleigh and Dawes limits for an obstructed aperture.

And this is the realm of the MTF where obstructed apertures pull ahead of even perfect unobstructed apertures - at those highest spacial frequencies. Some will say that tiny bit of performance boost near the Dawes limit is not significant because it is so often swamped by seeing. That's true, but I'd argue otherwise when it allows me to observe 7 tiny craters on Plato's floor or split tighter nearly equal doubles when seeing does not swamp that realm of the very tiny.

It's these types of observations that make me a believer in theory. Theory seems to explain seeing 'g' and 'e'. Most of us (maybe most of us, at least I do) think of diffraction limited as kind of a bad optic, nothing special, kind of blah. When in truth, diffraction limited even in a 150mm aperture is quite stunning to behold. And that beauty very often rests nearly entirely with the observing conditions and not the optic. But when your scope hits that diffraction limited performance, I am sure you will agree how so much nicer it can be.

So, the point being, I hope conditions permit others to observe 'e', 'g' in a modest aperture, or whatever other craterlets your aperture can theoretically resolve. If conditions are right, I am sure Nirv's 10" can nail many of the much smaller ones. I wish him, et al, Godspeed because I know it can be done.

Good luck and may you succeed - I want 'f'!

Edited by Asbytec (02/09/14 11:18 PM)


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6367424 - 02/09/14 11:26 PM

Quote:

As for Plato, A-E, W easy, and I would say that during a few really good cycles I noted g and h as more than just albedo features - they looked structural.




So, that's 8 for you, well done. Yea, specks were not as evident for me either, you're probably correct saying the sun angle isn't optimum. I'd bet you can count a lot more in a week's time. Get out your clicker.

So, your nose was bit off and my jaw fell off. We need a new hobby.

What do you recon your seeing was? You have a 10" aperture, which is ideal as it tends to be right at the aperture for the best atmospheric seeing. What you might see as 7/10, I might see as 8/10 or better in a 6". Being that 8/10 or better is diffraction limited, I would think your seeing was a tad less at about 7/10. Would that be a safe guess?


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edosaurusrex
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Re: Plato's challenge new [Re: Asbytec]
      #6367439 - 02/09/14 11:41 PM

Here are the predicted times for the Sun altitude to be 11.15 degrees rising, 12 degrees setting, at Plato's center to agree with Norme's sighting. Rising time plus a few days or setting time minus a few days should put viewing at the conditions stated in the earlier posts.

PLATO PREDICTIONS FOR 2014
MMM DD HHMM UT

FEB 09 1125 RISING *correlation*
FEB 21 1157 SETTING

MAR 11 0231 RISING
MAR 22 2356 SETTING

APR 09 1728 RISING
APR 21 1028 SETTING

MAY 09 0739 RISING
MAY 20 2013 SETTING

JUN 07 2042 RISING
JUN 19 0559 SETTING

JUL 07 0833 RISING
JUL 18 1629 SETTING

AUG 05 1923 RISING
AUG 17 0416 SETTING

SEP 04 0537 RISING
SEP 15 1733 SETTING

OCT 03 1553 RISING
OCT 15 0813 SETTING

NOV 02 0253 RISING
NOV 13 2345 SETTING

DEC 01 1509 RISING
DEC 13 1525 SETTING
DEC 31 0454 RISING


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6367446 - 02/09/14 11:50 PM

You're spot on the money Norme. I'd say seeing was P 7 in the good moments. Transparency was a bit off tonight, but that may help in crater hunting.

This evening I collimated several times as the scope cooled after noticing a few days ago the collimation does go off as the scope drops from +20 to -25C. Have to keep that up from now on. With familiarity I'm enjoying using the Astrosystems Lightpipe and auto-collimator. The Lightpipe has a feature that I heretofore had not used but I feel makes it better than a run of the mill cheshire.


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Re: Plato's challenge new [Re: nirvanix]
      #6367481 - 02/10/14 12:18 AM

Yea, collimation and cooling helped, without any doubt. Yea, I figured maybe just below 8/10 seeing other wise I am sure you would have nailed craters down to less than 1km. That opens up a bunch of them when the chance presents itself.

Transparency is interesting, I can tell a difference with Jupiter between descent and modest transparency. Of course, in the former it is also brighter affecting our perception. But, some thin humid overcast can affect Jove's softer contrast features, IME. At first, my own transparency was modest last night observing Plato with a noticeable haze around the moon. That cleared up in short order.

So, sure, transparency seems important even with lunar high contrast features (that are really low contrast on the focal plane when they are very small. Yea?) You just need that little extra contrast oomph to get the smallest ones, lessor transparency just get's in the way.

Rex, hey, what does the correlation mean? In your previous post you show "FEB 09 1412 RISING" as a good time, and above is adjusted to 1125UT. Does this mean the sun was at exactly the right angle - a sweet spot at 12 degrees - at that time instead of your earlier forecast? Or would 1412UT have been better?


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Re: Plato's challenge new [Re: Asbytec]
      #6369109 - 02/10/14 07:15 PM

Norme,

There was nothing special about the 12 degree Sun elevation when I made the original table. I figured a day after terminator crossing at 1/2degree per hour (12 deg) would be a good time to start looking. Your report noted you saw "g" at around 1100UT, or 3 hours earlier, so I corrected the Sun elevation for the RISING condition to agree (correlate) with your observation.

Ed


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Re: Plato's challenge new [Re: edosaurusrex]
      #6369154 - 02/10/14 07:40 PM

Rex, okay. Thank you.

Caught 'f' last night as a fleeting bright speck, but not in crater form. Seeing was such that 'e' was not held constantly.


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Re: Plato's challenge new [Re: Asbytec]
      #6369312 - 02/10/14 08:48 PM

I'll be going out shortly to look for more craterlets! Temperature gauge says -23C, a heat wave! Maybe I'll skip the second layer of goose down.

Norme, I used to have the Orion Starmax 127mm. Great little scope, especially in the tropics I would imagine. The diurnal temperature profile for my locale is very desert like so the scope was always chasing equilibrium. That's the reason I sold it, no qualms with the scope itself.


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6369329 - 02/10/14 08:59 PM

Nirv, understood. Yea, here in the tropics diurnal temps drop into the bone numbing 70's and tend to stay there. A Mak, any scope really, is in it's element.

Good luck, man. I'm hoping you can grab some smaller ones.


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azure1961p
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Re: Plato's challenge new [Re: nirvanix]
      #6369330 - 02/10/14 09:00 PM

Just to reiterate something here Norme - the smallish craters that are age old and worn will show a smaller shadow filled than a fresher crater with a well defined rim. Said another way, you might be able to see a smaller crate than you have if its fresh and better defined. Just some basalt for thought!

Pete


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mikewirths
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Re: Plato's challenge new [Re: azure1961p]
      #6370300 - 02/11/14 11:53 AM

Hi all,

SO I decided to re-visit a Plato video sequence that had some superb seeing. This time I stacked almost half the sequence and it pulled out finer details in the floor of Plato. Perhaps imaging this one day earlier would have been better, and more image scale too.

still its my best so far! 18" Starmaster, ASi120MM camera

http://imageshack.com/a/img850/9484/7ya0.jpg

cheers

Mike


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nirvanix
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Re: Plato's challenge new [Re: mikewirths]
      #6370421 - 02/11/14 01:12 PM

Wow Mike! You've got the whole alphabet there. Beautiful shot.

There's a crater in your photo that doesn't have a letter attached to it (in some of the previous posts), but I'm pretty sure I visually spotted it last year. Ah, just looked it up: it's f. Ok, Norme I have spotted f last year!


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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6370451 - 02/11/14 01:23 PM

Nirv, good on you. In crater form, I bet?

Mike, that is a great shot. I like the way you can tell why 'h' is more difficult than 'g'.


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nirvanix
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Re: Plato's challenge new [Re: Asbytec]
      #6370500 - 02/11/14 01:56 PM

Quote:

Nirv, good on you. In crater form, I bet?





Yes indeed, and depending on the sun angle, it's easier to spot than g or h.

PS - Mike, I love Mons Pico in your photo. It looks like a snow covered mountain. One of my favorite lunar objects.


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moonnerd
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Re: Plato's challenge new [Re: nirvanix]
      #6370955 - 02/11/14 06:47 PM

That photo is insane. Great work! Thanks for sharing with us.

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Asbytec
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Re: Plato's challenge new [Re: nirvanix]
      #6371308 - 02/11/14 10:15 PM

Quote:

Yes indeed, and depending on the sun angle, it's easier to spot than g or h.




You just amplified the challenge a lot.

I want 'f', too. If it's easier than 'g', hey...


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6371883 - 02/12/14 09:39 AM

Insane indeed - this is a new level of res for amateur instruments.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6371920 - 02/12/14 09:56 AM

Pete,

We in the northeast will have to wait for better seeing ... and for the snow and ice to melt. Also, not too safe carrying my 10" Dob down porch steps and around the corner of my house in slippery conditions.

Mike


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Mare Nectaris
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Re: Plato's challenge new [Re: azure1961p]
      #6371921 - 02/12/14 09:56 AM

But remember - there is one reference for even the most eagle-eyed observers: Chuck Norris does not *see* craterlets on Plato; they *reveal* themselves to him.



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nirvanix
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Re: Plato's challenge new [Re: Sarkikos]
      #6371961 - 02/12/14 10:16 AM

Quote:

Pete,

We in the northeast will have to wait for better seeing ... and for the snow and ice to melt. Also, not too safe carrying my 10" Dob down porch steps and around the corner of my house in slippery conditions.

Mike




Mike, my entire backyard has been a 6 inch thick sheet of ice for months. I still carry the 10" dob down two steps and plop it out on the ice many nights. You can do it!

Chuck Norris doesn't even require averted vision, he scares everything in to revealing themselves.


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Sarkikos
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Re: Plato's challenge new [Re: nirvanix]
      #6371968 - 02/12/14 10:20 AM

No I can't. I'm not Chuck Norris.

Also, plop, plunk and plonk are not good for sensitive optical instruments!


Mike


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Rareth
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Re: Plato's challenge new [Re: Sarkikos]
      #6372008 - 02/12/14 10:42 AM

Last night had some breaks in the clouds for Lunar Observations from MD., but of course with Brown due to deliver a new mount and tripod today....

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Sarkikos
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Re: Plato's challenge new [Re: Rareth]
      #6372038 - 02/12/14 10:53 AM

I don't think I'll be bringing out more than a 6" scope at home until Spring. But if the weather cooperates I will take my 10" Dob to a dark site during New Moon. It's actually safer dealing with heavy scopes there than at my house.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6372051 - 02/12/14 10:57 AM

Very nice detail.

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Re: Plato's challenge new [Re: Mare Nectaris]
      #6372315 - 02/12/14 01:13 PM

Quote:

But remember - there is one reference for even the most eagle-eyed observers: Chuck Norris does not *see* craterlets on Plato; they *reveal* themselves to him.






Chuck Norris trains a lot. Seek and ye shall find.


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Re: Plato's challenge new [Re: NeilMac]
      #6372421 - 02/12/14 02:05 PM

thanks for the "likes" guys! I think I can do better this year (if the seeing cooperates) I've made some improvements, like a 1/30th wave secondary,better camera, and a Zeiss Abbe barlow

cheers

Mike


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Re: Plato's challenge new [Re: mikewirths]
      #6373207 - 02/12/14 09:29 PM

Mike, according to measurements using quickmap, you are resolving craters down to 0.3 miles across. I have not done the math, but surely that's less than 0.5" arc - the average best the atmosphere can put up, they say. In terms of aperture, you are resolving down to 0.3 * 18, or 5.5/D(inches). That is totally consistent with observing 'g' in a 6" at 0.93 miles * 5.9" ~ 5.5/D as well. In fact, 'g' appears the same as your image. It's just a small with a dimmer floor as the smallest craters you imaged in crater form. In crater form, no less, and in excellent seeing, of course.

What's interesting is you are seeing shadows at about half that angular diameter. Pit shadows might be be crater form, but they are lacking the brighter rim. So, to see the rim, you need a larger crater consisting of a pit and a rim which means the angular diameter is larger than just a dark pit.

Now, that's interesting because I think I noted above having barely glimpsed dark pits on craters smaller than 'g' at ~0.9 miles. So, extended object resolution is a very complex thing depending on how you define it: crater form with rim, pit shadow only, or just a speck. And if so, then without doing the math, yet, 1.5 mile is about Raleigh limit. Down to about 0.75 miles would be 0.5R (the same empirical limit used for splitting very tight equal doubles.) I am not sure how 0.5R applies or correlates between extended object and point source resolution, but the thought they may have a similar empirical limit is interesting.

I think as long as the shadow and rim is 5.5D, you /could/ see it in crater form if seeing permitted. The aperture is capable of that, conditions might not be. At higher sun angles, the pit shadow shrinks and disappears. We loose the crater. We might resolve it in terms of angular resolution, but it's not visible to us because the contrast is gone. But, we should be able to see pits down to about 3/D because 5.5/D includes room for the brighter rim and the pit shadow. But just barely, fleetingly, and only in perfect seeing (cooled and collimated, of course.)


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azure1961p
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Re: Plato's challenge new [Re: Asbytec]
      #6373255 - 02/12/14 09:58 PM

Well it makes sense - though I haven't done it - knowingly. I've seen those pepper specks wavering but never made a concerted effort for measure. Though I can't join in on these observations due to a number of seasonal reasons - I'm saving it all for better sky's and snow free ground!

It makes sense - the same sense though of a different dynamic in resolving doubles as elongated down to .5/Raleigh.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6373325 - 02/12/14 10:29 PM

I think so, too, Pete, need to think on it some more. I believe 9/D is a great rule of thumb for what we can see on an average night. It's consistent with the big four being difficult at times. However, I think we can do better down to 5.5/D as an aperture - diffraction - limit rather than a seeing limit.

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Re: Plato's challenge new [Re: Asbytec]
      #6373650 - 02/13/14 07:05 AM

Crunching some numbers for a 150mm aperture viewing the moon at 250,000 miles (400,000km) on 9 Feb 1125UT, Seeing 8/10 Pickering, Transparency 4/5, at 320x with 6mm TMB II.

Raleigh is 0.92" arc, 1.1 Miles or 1.8 Km
CO is 0.83" arc, 1.0 Miles or 1.6 Km

Dawes is 0.77" arc, 0.9 Miles or 1.5 Km
CO is 0.70" arc, 0.8 Miles or 1.4 Km

Lambda/D is 0.76" arc, 0.9 Miles or 1.5 Km
CO is 0.68" arc, 0.8 Miles or 1.3 Km

Raleigh/2 is 0.46" arc, 0.6 Miles or 0.9 Km
CO is 0.42" arc, 0.5 Miles or 0.8 Km
------------------------------------------------------------
Crater diameter below were measured from quickmap.

Crater 'g' is 0.67" arc, 0.8 Miles or 1.3 Km - Seen in crater form
Shadow is 0.54" arc, 0.7 Miles or 1.0 Km - Seen

Crater 'h' is 0.57" arc, 0.7 Miles or 1.1 Km - Larger not seen in crater form
Shadow is 0.43" arc, 0.5 Miles or 0.8 Km - Larger possibly seen once or twice as fleeting dark spot
------------------------------------------------------------
Seeing crater 'g' seems to correlate nicely with the CO modified Lambda/D limit just below Dawes. That appears to be impossibly small, yet it was surely seen regardless of what I think about it. Observing 'g' might actually make sense as this is where the FWHM of two 6th magnitude stars just begin to touch. It is the limit of resolution in that sense. I'm not sure of the correlation as the moon is an extended object. Still, it does not change the fact 'g' was observed and is reasonably consistent with the smallest craters Mike resolved in his aperture.

Possibly observing a dark spot at 'h' (presumibly the larger of the two) seems to /suggest/ resolution approaching 0.5R as modified. This is near an empirical limit for viewing very tight, bright, and equal doubles. Right now that is just interesting and not conclusive. But, it's interesting if 'h' shadow was about 80% of it's pit diameter on the date of the observation. (That figure was assumed for 'g', as well.) Despite 'h' being a double crater, I saw neither nor did I see them as one elongated form. Crater 'g', however, was seen clearly at least 3 times during this observation.

In any case, the observation of 'g' and lack of observation of 'h' seems to suggest the 0.1 mile difference in their diameter (as measured on quickmap and is an approximation) might define an extended object resolution limit near this angular diameter. And it's not so much about being eagle eyed as it is with the aperture and conditions. If it wasn't on the focal plane, it would not have been seen.

By the way, 'e' was held in crater form for long periods of time, 'g' was fleeting in crater form (as 'f' might be if confirmed), 'h' was not much more than a blurry something that /may have/ offered a dark spot from time to time. Crater 'i' was another potential dark spot about the same diameter as 'h'. Below makes some intuitive, progressive sense to me:

Crater 'e' at 1.0 mile across: easily held for long periods.
Crater 'g' at 0.8 mile across: fleeting, but crater form.
Crater 'h' at 0.7 mile across: the larger nor the pair not seen except as /possibly/ a rare and very fleeting dark spot only possibly glimpsed. I know that sounds weird as maybe the pair could be seen as one. Wish I could say they were, but they were not.

Edited by Asbytec (02/13/14 07:51 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6373868 - 02/13/14 10:37 AM

Hi Norme,

Great report...

That E and G were held in crater form, ie; shadow, rim, brighter sunlit side of crater, would clearly suggest the 9/D rule is in need of some revision. I think it still holds merit but not with any particularly stringent threshold rule.
I know Ive seen crater "spots" well past but without certain measure how far.

I could see how H might appear as a transient blemish - that's the ragged edge Norme. The peril here though is in the double crater slurring together to form a pseudo crater form - somewhat like two threshold faint stars of fine seperation appearing as one faint star - brightness combined.

Harold Hill whose got the excellent portfolio of lunar drawings book in an interview I believe stated with his ten inch reflector he was gliding stars down to a third of a mile or so in Plato. It was a sky and tel article interview - wish I had the certain number - it was clearly under half a mile though.

The 80% pit shadow would seem to be a player here - got all crater involved Id think. I don't really know - the 80% shadow fill would seem optimum but at some point the low sun angle darkens the surrounding terrain so much its a matter of diminishing returns. The angle of the terrain could be a big player here too. Its something to ponder as there's a lot involved potentially to create that exceptional view.

Pete


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nirvanix
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Re: Plato's challenge new [Re: azure1961p]
      #6373900 - 02/13/14 10:52 AM

Quote:



Harold Hill whose got the excellent portfolio of lunar drawings book in an interview I believe stated with his ten inch reflector he was gliding stars down to a third of a mile or so in Plato. It was a sky and tel article interview - wish I had the certain number - it was clearly under half a mile though.

Pete




Thanks Pete,
What exactly did he mean by 'gliding stars'? I take it he spotted something like a speckle of light that he knew to be a crater? That gives me encouragement to go after the smaller craters in Plato when seeing allows.


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Re: Plato's challenge new [Re: nirvanix]
      #6373925 - 02/13/14 11:16 AM

Yea, Pete, the low angle contrast is something I am still mulling over. That was very evident when Nirv and I observed Plato on the 8th. On that night, 'e' was faintly seen as a tiny fleeting crescent of light. All of them were. They were much cleaner the following night. On the 8th, just as Plato was leaving the terminator, the contrast between it's floor and the crater pits was just too low (for me) to see. However, the faintly lit rims could be seen.

I am not sure 9/D has to be revised. We just need to differentiate what it is telling us. It's a great rule of thumb for resolution in average seeing - an atmospheric limit. It is not a diffraction limit based on Raleigh or anything else.

That limit seems to be much smaller. If you perform the math above on Mike's image, you will get consistent results with a much smaller diffraction limit on the order of 5.5/D. That's what his resolution of craters 0.3 miles in diameter proves - it was on the focal plane. It was resolved. As for highly processed images, there may be a difference in processing bright low contrast objects like Jupiter and bright high contrast objects like the moon. But, Mike's images prove such small resolution is possible. I hope to have proved it can be seen.

Edited by Asbytec (02/13/14 11:48 AM)


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azure1961p
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Re: Plato's challenge new [Re: nirvanix]
      #6374233 - 02/13/14 02:04 PM

Quote:

Quote:



Harold Hill whose got the excellent portfolio of lunar drawings book in an interview I believe stated with his ten inch reflector he was gliding stars down to a third of a mile or so in Plato. It was a sky and tel article interview - wish I had the certain number - it was clearly under half a mile though.

Pete




Thanks Pete,
What exactly did he mean by 'gliding stars'? I take it he spotted something like a speckle of light that he knew to be a crater? That gives me encouragement to go after the smaller craters in Plato when seeing allows.




Glimpsing craters!!!! - gliding stars" was my creative auto-correct at work - lol - sorry for the confusion.
Pete


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Re: Plato's challenge new [Re: Asbytec]
      #6374265 - 02/13/14 02:34 PM

After a little revision (and using the LRO PDS Archive Interface for better projection), here are the diameters of the craterlets in Plato that I labeled in my original article:

LUNAR ORBITER RECONNAISSANCE CAMERA CRATER DIAMETERS
FOR CRATER PITS INSIDE LUNAR CRATER PLATO
(diameters +/- 0.03 km)

Craterlet A: 2.48 km (1.54 miles), Craterlet B: 2.00 km (1.24 miles)
Craterlet C: 2.20 km (1.37 miles), Craterlet D: 1.91 km (1.19 miles)
Craterlet W (west wall): 3.13 km (1.94 miles),

Craterlet e: 1.73 km (1.07 miles), Craterlet f: 1.46 km (0.91 miles)
Craterlet g: 1.40 km (0.87 miles),
Craterlet h (triple crater feature 2.24 km x 1.19 km (1.39 miles x 0.74 miles))
components "h-1": 1.19 km, "h-2": 1.08 km, "h-3": 0.79 km

Craterlet i: 1.27 km (0.79 miles), Craterlet j: 1.09 km (0.68 miles)
Craterlet k: 0.95 km (0.59 miles), Craterlet l: 0.94 km (0.58 miles)
Craterlet m: 0.91 km (0.57 miles), Craterlet n: 0.87 km (0.54 miles)
Craterlet o: 1.10 km (0.68 miles)
Craterlet p (triple crater feature approx. 1.8 km x 1.5 km (1.1 mi. x 0.9 mi.))
(components: p1: 1.27 km, p2: 1.04 km, p3: 0.57 km)

Craterlet q (doublet): 0.78 km (0.48 miles)
Craterlet r: 1.19 km (0.70 miles)

Craterlet h is a triple (2.4 km x 1.19 km roughly), so it is difficult to resolve as anything but an irregular albedo feature. Again, you cannot use Dawes Limit for extended detail on the moon. All you can do is see what you can see. Clear skies to you.


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Sarkikos
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Re: Plato's challenge new [Re: David Knisely]
      #6374538 - 02/13/14 05:35 PM

Great info, David. Accurate to +/- 0.03 km! Thanks.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6374603 - 02/13/14 06:16 PM Attachment (10 downloads)

David, that 'g' is closer to 0.9 miles makes sense, it's actually more consistent with Mike's image than being 0.8 miles. I got 1.3km (0.8 Miles) from rim to rim using quickmap. Thanks for the work to get a better measurement. That changes the results above slightly from obstructed lambda/D to obstructed Dawes criterion. (And it's actually consistent with my tightest double star with dark space split to date: STT507 is 7 and 8 magnitude pair reported at ~0.7" arc or maybe slightly wider near 0.72" arc.)

Thinking more about this, it may have been that Plato's floor actually improves the chance of resolution. If we can think of extended objects as an infinite number of spurious discs, then Plato's darker floor would consist of smaller discs than those comprising brighter lunar surface.

One would think at such small scales, however, that higher contrast would be needed in line with their spacial frequency. Indeed 'g's floor was faintly grey. Apparently we can get away with some unknown level of high contrast instead of 100% contrast required at frequencies near and above Dawes or Raleigh. I'm not sure what contrast level is required, but it does not seem to be 100%. Maybe just being a "high contrast" lunar object is good enough.


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Re: Plato's challenge new [Re: Asbytec]
      #6374858 - 02/13/14 08:47 PM

Norme the dark floor would not be to an advantage however if the brighter partitions of the craft puts are that much darker as well.

Mike, Id think the error is greater than .03 simply and it has nothing to do with absolute accuracy of the image resolution but that ambiguous transition between plain, crater rim and crater floor. Fresher craters make easier work of this but its still has this null zone that can be challenging in knowing where to consistently draw the line. When you get into the details it gets hard to get better accuracy a lot of times than a quarter mile. Defined rilles can make this An easier task. My finds anyway. Id guess accuracy is generally between .10 and .20 depending in target.

Pete

Edited by azure1961p (02/13/14 08:48 PM)


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Asbytec
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Re: Plato's challenge new [Re: azure1961p]
      #6374897 - 02/13/14 09:07 PM

Yea, Pete, our findings can only be as accurate as our measurements of various features and their characteristics, especially as seen from a distance. I am not sure how accurate these tools are. For a 6", there is some variation of about 0.1 mile difference between Raleigh (1.0), Dawes (0.9) and Lambda/D (0.8). Raleigh could be 1.1 to 0.9, Dawes 1.0 to 0.8, etc. So, our best guess is to measure as best we can and work with as few significant digits as possible.

Still, so far, 'g' can be seen and 'h1' cannot. So whatever size they are seems to hint they define boundaries to the diffraction limit - until someone reports 'h1' as resolved. Then we convert them to some resolution criteria so we can apply them to different apertures. Then seeing decreasing with aperture at increased resolution begins to complicate things further.

Yea, it is all about having enough image contrast transferred to the focal plane, a certain object contrast, and the feature has to be large enough to be seen. For a diffraction limit, per experience and Mike's images, that seems to be near 5.5/D on a very good night. As for contrast, well, might need some way to measure it. However, empirically, one day out of the terminator, there was not enough contrast - for me. One more day's increase in sun angle provided enough contrast - for me, on that night, in the conditions present. So, whatever those levels of contrast were seems to define what is needed. I am sure it was not 100% during either observation.

Edited by Asbytec (02/13/14 09:29 PM)


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Re: Plato's challenge new [Re: Asbytec]
      #6374939 - 02/13/14 09:24 PM

Hi Guys,

Interesting discussion! Of course any image is a static representation of many tiny moments of best seeing, so the visual experience is much more dynamic. But I wonder if these tiny "at the limit" features that are more spots than resolved craterlets are also bound by the quality of a given nights transparency (and not just how good the seeing is). A mountaintop observing session with equal good seeing compared to say a really good night in the Fla keys should be superior in terms of ferreting out the smallest low contrast spots.

just my 2 cents

Mike


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Re: Plato's challenge new [Re: mikewirths]
      #6374973 - 02/13/14 09:36 PM

Mike, great point...and as you can tell, I find the discussion fascinating, too.

Yea, transparency seems to be a factor, of course depending on how good or bad it is. You cannot see anything with overcast skies - exaggerating to make a point.

Particulates, as I understand it, cause humidity to become more opaque and scatter(?) light. This scattered light would seem to dim contrast. And if significant, likely could affect detection of smaller, grey crater floors presumably already hampered by diffraction contrast loss.

By the way, I'd think memory of that observation is much like your static image being that it consists of three still frames of 'g', as well.


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Re: Plato's challenge new [Re: Asbytec]
      #6375381 - 02/14/14 02:51 AM

Asbytec wrote:

Quote:

David, that 'g' is closer to 0.9 miles makes sense, it's actually more consistent with Mike's image than being 0.8 miles. I got 1.3km (0.8 Miles) from rim to rim using quickmap.




The "line" tool in Quickmap appears to underestimate linear size by as much as 3.7 percent. I use the PDS Archive Interface and then use the scale on the lower-left of the images to get diameters. Most of the problem with the diameter estimates is getting a precise location for the opposing rims, as with the highest resolution images, determining the crest of each rim can be a little imprecise (hence, the +/- 0.03 km figure, which might be a hair liberal, as the error could be as much as 0.05 km or even slightly more). Clear skies to you.


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Re: Plato's challenge new [Re: David Knisely]
      #6375385 - 02/14/14 03:03 AM

Agreed, David. It's not so hard to know resolution and estimate how large that would be at a distance. It's a little more difficult to measure something and determine resolution. Anyway, we do the best we can. I find this whole observing challenge and the discussion fascinating.

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Re: Plato's challenge new [Re: David Knisely]
      #6375593 - 02/14/14 08:48 AM

Quote:

Asbytec wrote:

Quote:

David, that 'g' is closer to 0.9 miles makes sense, it's actually more consistent with Mike's image than being 0.8 miles. I got 1.3km (0.8 Miles) from rim to rim using quickmap.




The "line" tool in Quickmap appears to underestimate linear size by as much as 3.7 percent. I use the PDS Archive Interface and then use the scale on the lower-left of the images to get diameters. Most of the problem with the diameter estimates is getting a precise location for the opposing rims, as with the highest resolution images, determining the crest of each rim can be a little imprecise (hence, the +/- 0.03 km figure, which might be a hair liberal, as the error could be as much as 0.05 km or even slightly more). Clear skies to you.





Exactly - its a little dicey but I did enjoy doing that on some areas . Id like to do it here but alas a lousy laptop.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6390066 - 02/22/14 09:00 AM Attachment (15 downloads)

Here's what I think is happening with Plato g...in terms of contrast.

Again, Mike resolved down to 0.3 miles in an 18". A third of the aperture is a third of the resolution, so 6" should resolve 0.9 miles - a third as good as three times the aperture.

Resolution is not a problem. Image processing enhances contrast, not improving resolution (far as I know.) So, 'g' is a contrast problem, and this has to be the solution. I suspect we're essentially looking through the rim's first diffraction inter-space which is not opaque to objects within it.

There is an intensity drop off between two PSF at the Dawes limit. Because the opposite point is much less intense than an equal double Dawes split, that intensity drop off between the peaks is much deeper - enough to be seen after contrast transfer. That has to be the case.

The first inter-space fro a 150mm 31% obstructed aperture is ~ 0.83" arc. Plato 'g' had an angular measure of about 0.72" arc - just above an approximate Dawes limit (~ 0.70" arc) for the same optic.

The graphic is not to scale, I wish I had the data to make it so. It's only an illustration of the concepts involved. The light blue rectangular area shows an approximate gap greater than 5% contrast between the visible edges of two opposing spurious discs.

Edited by Asbytec (02/22/14 09:30 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6390266 - 02/22/14 11:04 AM

Good thoughts Norme. Can't remember whether you stated or not that you resolved g in your 6" to your satisfaction?

Not sure if Mike's image processing software does it , but there are mathematical/software methods (interpolation) for increasing resolution. I dabbled in it about 3 decades ago (yeesh!). For example, a recent paper:

Resolution by interpolation

It could be that if you hit a 'sharpen image' button in the software it's doing something of the sort.
For g and h I've gotten more than just a bright 'pixel' in my observations, more like a collection of light and dark pixels. Wonder if my brain performs some sort of interpolation to make it seem like something structural.

Maybe I should haul my dob over there and we can do some comparisons.


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Re: Plato's challenge new [Re: nirvanix]
      #6390488 - 02/22/14 12:51 PM

Nirv, the thought hasn't escaped me that our eyes actually see nothing - our brain processes input. Maybe there are some mysterious tricks at work that cause the brain to see what it wants to see. For all we know the entire world is an illusion and one person's green is another person's red. I am no expert on all that, how to make it work, or when it just happens spontaneously. But, yes, I did "see" 'g' in crater form - much to my own amazement.

I didn't "want" to see it so badly that my brain would have been motivated to do the trick for me. I didn't even know whether it could be seen or not. No clue. I was just happy to have gotten 'e.' I expected maybe a white speck - my brain should have processed that desire into reality. But, there 'g' was plain as day...thrice.

Yea, I image some image processing software cleans up an image - tightens up some stray light and puts it where it's supposed to be. But, if the optic does not resolve the feature, the software has nothing to work with to process a resolved image from the raw image of the focal plane. (Barring having read your paper.) I just don't know much about the topic beyond that, or whether if what little I do think I know is accurate.

In any case, my brain processed it and I saw it. And it's consistent with Mike's image. So, what's a guy to think?


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Re: Plato's challenge new [Re: Asbytec]
      #6390661 - 02/22/14 02:43 PM

Quote:

For all we know the entire world is an illusion





I think you're on to something there Norme!

I'm sure you got g.

As for interpolation, it's amazing what you can 'resolve' using the right algorithms. All you need is some pixels and you can see things that are beyond the power of your optic. Of course there's a small amount of uncertainly in the result, as they are ultimately a deductive guess. This has military application among other uses, and I suspect the mathematical formulation has become quite complex.


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Re: Plato's challenge new [Re: nirvanix]
      #6390715 - 02/22/14 03:25 PM

Our eyes register sense data, our nerves transmit the signals, our brain sees the world.

The world is not an illusion. Objective reality exists. But the path to it is not direct.

Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6391294 - 02/22/14 09:45 PM

Quote:

Of course there's a small amount of uncertainly in the result, as they are ultimately a deductive guess.



I cannot say I have ever seen ghosts or alien spacecraft. Yes, sometimes even I doubt myself sometimes, maybe we all do. Especially over time. One might begin to wonder if they really saw that thing. Uncertainty creeps in.

But, one thing is certain. My brain processed a image of something that looked like a tiny crater where 'g' should be. I guess that's all one can say with any certainty. The vision is still in my head and without uncertainty about that 'processed' mental image. So, one has to ask if we saw it or imagined it. Is it real or some magic trick designed to fool us.

If I imagined it, then I cannot trust the image of my monitor sitting in front of me, either, as I type some imaginary letters into what looks like a text box. If not, it can be said we do not see craters or monitors. Nor feel, smell, taste or hear them, either. We cannot trust our senses, or can we just not trust our brain?

I think Mike is correct. The world is real and we perceive it as such, unless we're being fooled by some slight of hand, misdirection, or bump in the night. For most sane folks, I am sure the brain doesn't make things up unless it has no data to explain something. Well, it must be a ghost, in that case because we don;t know what it really was. Our brain might have trouble interpreting that bump in the night we actually heard coming from somewhere. We might think it came from a monster under our bed when in fact it was dishes settling downstairs.

I trust my eyes enough to believe when I am focused and observing - seeing nothing unusual, something that should not be there, something that does not make sense, or cannot be explained - then the mind is acting rationally and the object can be said to exist. It's not like a magic trick where the magician's coin is not in the hand we think it is - nature is not trying to fool us.

If we cannot trust our senses and perception, then millions of years of evolution have been for not developing our senses and perception to just make up the world around us as we travel through it. There would be no reason to trust the sensations at my finger tips as being keys on a keyboard with the proper letters printed on them.

If we can trust our senses and perception, then the task become to describe it in the context of theory that describes what we should and did see - in reality. Science explains what we do see in the best way we can explain it. Maybe the only fooling we suffer from is the illusion we do not see (nearly) everything explained by theory. So, instead of fooling ourselves into not seeing them, we interpret theory in such a way that explains why we do not - when in fact we should.

In the end, if we cannot trust what we see and explain it using an interpretation of theory, then we're limited to observing the easy stuff. I've seen it many times. So, why observe at all, if what we see is not real. Because we enjoy our overactive imaginations? That's not worth staking my reputation on - success is.

Edited by Asbytec (02/22/14 11:40 PM)


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Re: Plato's challenge new [Re: Asbytec]
      #6391559 - 02/23/14 01:19 AM

Interesting illustration Norme.

Still trying to wrap my head around it. This may be interesting though...

We know the point spread function classic profile as illustrated - bright point on a darker back ground. Okay - and them I see how you are working the crater into this but for clarity - how about this...

Forget the crater and its rim and so forth. Make an illustration of a surface area of overlapping PSFs surrounding a small black dot. No rim or anything / just a clearing in the PSF forest of profiles - how would this illustration look in profile surrounding a 1 arc second black dot? Arrive at that first - then later add the rims and so on.

We ever have the stellar point PSF against black space. Lets see a negative of this by inverting contrasts. Black spots won't form a PSF but it'd be interesting to see how the bright overlapping points frame and even irradiate into it.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6391630 - 02/23/14 02:16 AM

Pete, it depends on how intense those intensity peaks are. If they are equally bright and we can see them to FWHM, then we'd essentially have a Dawes split circling a tiny black spot in the center that would appear very grey. Being completely encircled, though, it's likely that dark spot would disappear from view all together, especially one at Dawes. Maybe not one at Raleigh or above.

I have thought about the idea and I am not sure how to explain it, really. The only explanation I have (other than some mental illness or propensity to fool myself) is those spurious discs surrounding the crater pit have to have a diameter smaller than FWHM (approximately)...so their edges do not visually touch at the obstructed Dawes limit.

This is why it would help to either know how bright two or more tiny point sources are on the moon or to better understand the mechanics of infinite spurious discs on extended objects. If we apply infinite spurious disc method, the above is the best I can come up with. It's the only model I am aware of and it uses dark space resolution in terms of Dawes or Raleigh.

There may very well be something else at work describing extended object resolution - a different model than describing it in terms of infinite points. That's what makes this observation so interesting and unbelievable. It's interesting and above reproach, so I try to explain it. It's unbelievable because no one else has explained it interpreting theory with conventional understanding of what is or is not possible.

Maybe neither really apply, even though it appears Dawes might. If Dawes appears to be the limit in this particular case, then maybe the best one can say is Dawes applies. The real answer is, it can be done. I thought 'e' was a limiting observation of a dark crater pit on a dark floor. It's not, not for a single crater.



Edited by Asbytec (02/23/14 04:16 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6391705 - 02/23/14 04:21 AM

What you are describing might, however, better apply to 'h'. It seems one should be able to easily resolve it's elongated shape. It's plenty large in that axis. The problem seems to be each is very small to begin with, smaller than 'g'. But it's further complicated having two bright rims involved separated by about the diameter of 'g' given the space between them.

One bright rim belongs to one crater and the other to it's neighbor near the middle of this east to west elongated form. Being individually smaller than Dawes and having two bright rims (slightly further separated to near Dawes) might make one of them sandwiched between the two bright rims (depending on the sun's direction) unresolved as a brighter speck. (Maybe even a Dawes split of the bright rims, though, imagine that.) The other with one associated rim, who knows. A fleeting dark spot?

Anyway, the spurious discs have to be small. Imagine 1.6" arc Ganymede having a point on its limb. If that point was at FWHM, it would be about lambda/D ~0.70" arc larger on each side. In other words, Ganymede might appear to be as large as 1.6" arc (actual) plus another 1.4" arc (diffraction) or about 3" arc in diameter. It might appear a little bigger, but I don't think it's nearly twice as large as it should be.

So, something is happening on extended objects or Dawes is happening but we have to interpret it as narrow peaks of lessor intensity. If so, this opens up the Dawes gap. On Ganymede, this makes some sense due to limb darkening. That same darkening may apply to craters on Plato's floor - but not on brighter lunar terrain and despite the improved object contrast. In this case, the improved contrast is a hindrance.

Edited by Asbytec (02/23/14 04:41 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6391785 - 02/23/14 07:22 AM Attachment (7 downloads)

Is the Airy disc opaque? When looking at a star we might be forgiven for thinking it's diffraction image is opaque. All we see is a rather evenly lit bright disc and some rings with dark spaces separating them. But, why do we see black space at all - there's a disc in the way. Sure, the black inter-space defines an intensity minimum in the disc's structure and also to the eye. But, the disc itself is not black and opaque to objects behind it. The black we see comes from the lack of light from space itself. The space behind it is black.

In an abstract way, if space were red then the diffraction inter space would be red. Now, I understand if we saw red that it would imply the presence of longer frequency light waves subject to the diffraction of the same optic. A red point source would have an inter space where light is cancelled a that would appear black. But, it would be transparent - this is why one Airy disc does not blot out a companion star inside the first ring and Dawes splits are possible.

On an extended object things get interesting because there are infinite numbers of tiny spurious discs comprising not only the point source in question, but every point source surrounding it. And since each PSF is transparent, we can - at some point - begin to see discs "though it" as it's intensity falls off and the other is bright enough to show through. The Airy disc does not obscure everything behind it making resolution impossible. With individual stars, there just is nothing but the waveform diffraction image to see. On tight doubles, there's a companion. On extended objects there are infinite nearly equal "companions" and we can see them and through them.

But there is an example that might explain what I mean. And it may help explain why such small dark things can be seen on the moon as we look "through" the PSFs formed by a brightly lit curved crater rim. This concept hit me observing Moltke. I wondered why I only saw one diffraction arc when it's rim was very brightly lit.

Motlke's rim Was bright enough to produce a diffraction artifact. Between that artifact and the bright rim I saw the normal dark inter-space just like the one formed in an Airy pattern. The space between them was black because the moon was black. Away from the sun, Moltke's walls case a nice black shadow and I could see that shadow right up to the bright rim. In fact, the diffraction artifact cut across it (and, I suspect, filled the interior which was also black.)

So, black was seen and not so surprising until you realize it's not the dark inter-space we are seeing - its the shadow cast by Moltke we're seeing. The intriguing observation came when I realized there was no visible diffraction artifact on the sunlit side of Moltke's rampart. I could see the sunlit rampart right up to the black crater pit (or up to the diffraction limit.) Suppose there was a diffraction artifact over the bright sunlit rampart, but it's contrast was too low to be seen. But, I was not seeing black through the minimum inter-space, I was actually seeing Moltke's bright grey rampart.

This seems to suggest the diffraction PSF is not opaque, it much be transparent. And if it's transparent, it's possible to look through it and see a crater pit or something else - provided it subtends an angular diameter larger than the brightest portion of the spurious disc(s). And if that nearby point source reflects any light at all, the closer into the spurious disc we can see it. Especially if it's much brighter, in which case the brighter one would dominate the fainter one. If they are the same intensity, they move pretty close together (Sparrow limit) and we see both with a constant, unresolved intensity. If one is dimmer, it still shows "through" the brighter one, but only to a point it's intensity is the same as the dimmer one...then the dimmer one blends into the brighter one and disappears.

I am not sure how this applies, but certainly being transparent might mean higher resolution up tp the Dawes limit for bright extended objects because we can see through the PSF of the brighter source. At Dawes is where the brighter PSFs become too bright to allow anything at smaller angular separations to show through and be seen...unless that very close object is tad brighter and begins to dominate the scene (such as bright craters on Ganymede, they are brighter than surrounding PSFs, but not so bright as to completely dominate all of Ganymede's disc. I bring this up because, while Ganymede lacks black spaces allowing black diffraction inter-space to be seen thus defining resolution, it does have slightly brighter bright spots in it. The same thing is happening on Plato's floor, except there are black spaces to be seen through the transparent spurious discs as soon as the intensity falls below the visible threshold.)

Edited by Asbytec (02/23/14 07:24 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6391821 - 02/23/14 08:30 AM

The reason I bring this up (above) is because there has to be something magical happening to allow such fine resolution down to Dawes on lunar extended objects. Normally we think of resolution as a hard and fast number, like 113.4/D, and that's it. This implies a hard radius through which nothing closer can be seen. And it makes intuitive sense because the spurious disc does not appear to have a gradient when indeed it does have one.

But, if the Airy pattern is transparent, then resolution becomes a function of intensity rather than a hard radius limit. The bright circle of intensity through which nothing closer (and of equal brightness or dimmer) can be seen can vary widely in angular size depending on it's intensity and the eye's response to that intensity.

Take Ganymede for example quoted from above.
Quote:

Anyway, the spurious discs have to be small. Imagine 1.6" arc Ganymede having a point on its limb. If that point was at FWHM, it would be about lambda/D ~0.70" arc larger on each side. In other words, Ganymede might appear to be as large as 1.6" arc (actual) plus another 1.4" arc (diffraction) or about 3" arc in diameter. It might appear a little bigger, but I don't think it's nearly twice as large as it should be.



I wish I knew the apparent angular size of Ganymede in a 150mm aperture due to diffraction. Knowing this could allow one to estimate the size of the visible spurious disc along Ganymede's dimmer limb and even if Ganymede's limb darkening is not entirely pronounced visually. At about 5th magnitude in total, I'd wager those limb point source discs are pretty small and do not expand Ganymede's apparent diameter all that much (I think Astrojensen argues this point.) If so, then the same process can be happening on the moon - and smaller spurious discs mean higher resolution. Maybe the effect is not all that great, but if it's any smaller than lambda/D (as an approximation for Dawes) then Dawes level resolution seems very reasonable.

Edited by Asbytec (02/23/14 08:34 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6392058 - 02/23/14 10:59 AM

The problem I am trying to solve is why 'g's floor was light grey instead of black. Diffraction is the obvious answer, but how. It's outer rim subtending only 0.72" arc diameter easily fits within the first minimum at 0.83" arc radius and is well within the diffraction ring produced by any point on it's edge. That ring is well beyond 0.83" arc, anyway, out beyond the crater's entire diameter. So points along the crater (and brightly lit rim, especially) do not contribute loss of contrast overlapping their rings structures.

Especially noteworthy, is at 0.72" arc in diameter it fits neatly inside the first minimum of the brighter rim diffraction. The second maximum (first ring) is well outside the pit - so how does this ring overlap the pit destroying contrast. It doesn't. In that case, are dimmer PSFs further out in angular diameter from g's pit center overlapping their own first ring into the pit? Or does the intensity profile bordering the pit still have some energy as it closes the gap with other profiles along the edge of the image - thus contributing to the less than black contrast transfer of the black pit? I suspect the latter might be the case, and if so, the edge of the PSF extending into the pit would have to be transparent in order to see the pit through it.

Put an infinite amount of transparent (to the eye) peak intensities lining the crater's perimeter together and you might get a small build up of light across the pit - enough to turn it grey when the image is transferred through the optic.

Forget the rings causing any problem, the floor is relatively dim further out and the rings are probably not seen at all, anyway. Or at best extremely dim. But, as for the PSF, maybe it's insufficiently bright to be seen, but many of them can build up enough intensity across the pit to grey it out. In any case, the PSF does subtend across the pit because it extends all the way out to 0.83" arc, anyway. The peak intensity extends out to the first minimum beyond the pit and so covers the black pit with some energy. It has to. So maybe it's the cause of the contrast transfer rather than the much dimmer first rings of much less intense points further out.

Edited by Asbytec (02/23/14 11:13 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6393122 - 02/23/14 08:44 PM

I'm not fully understanding the spot inside Moltke - is this something you saw or a theoretical point?

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6393390 - 02/23/14 11:26 PM

Well, I did see a bright point inside Moltke, I just didn't know what it was. Was it a feature on the floor? If so, there has to be a feature present that can be seen in a 6" scope under the conditions present. That does not appear (really) to be the case. There are some rocks down there, but one might imagine they are not easily resolved. So I suspect it was a diffraction artifact and tried to explain it as such.

But, the observation was enlightening as the crater's parts were visible "through" diffraction artifacts and not blotted out by them. There is something about this effect that seems to allow 'g' to be observed at Dawes for a 150mm obstructed aperture. I am exploring that reason and I think Moltke holds a clue.


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Re: Plato's challenge new [Re: Asbytec]
      #6393686 - 02/24/14 05:22 AM Attachment (9 downloads)

Here's the problem. When I observed 'g' it was in crater form plain as day - it looked like a crater and not a Dawes split. It was bright on the lit rim , grey across the pit, and a little brighter across Plato's floor. It looked like a crater in exactly the same way Mike's image shows them. Exactly. It was not a series of intense and less intense spots (and would not be with infinite points), nor was the floor simply looking like the dark space between two brighter points as in a Dawes split.

In order to see the crater, I have to be able to see through the PSF (light yellow in the image below). At some point I cannot see through it (dark yellow in the image below) because there is nothing brighter to see. But there is something darker to see.

When we see the Airy disc set against the high contrast blackness of space the eye sees a bright spot and interprets it as not having a gradient. It's just bright and the eye sees that. Intensity simply falls off abruptly giving the disc it's edge at about FWHM. There is nothing so see behind that intensity gradient in the vastness of black space - the eye just sees something bright. (By the way, the gradient is visible in much longer focal lengths, but not in amateur focal ratios.)

On the moon, an extended object, there is something fairly bright to be seen very near any given point and right up to and including that point - as Moltke shows. As such, the eye no longer has that high contrast black of space to compare brightness with. It's possible than on extended objects the eye does, indeed, see the PSF gradient - which very rapidly falls off to the intensity surrounding it leaving a very small radius. Actually nothing but a point exists because of the gradient.

We do not see each point down to FWHM as we do in the void of space without light, we see only the very peak of each point source intensity infinitely close together. If the surface is uniform in intensity, each PSF has no visible radius - it's just a point. But, you can see the point next too it of equal brightness because each PSF itself is transparent, other wise you could only see one of them at a time and not all of them simultaneously by looking through each of them. If it is brighter, then it's brighter radius increases a tiny bit and outshines points directly near it.

The PSF gradient is seen not to FWHM on extended objects, it is seen to the intensity of the points adjacent to it. It's that intensity difference than defines the radius of the visible disc hence resolution. On bright extended objects, the background intensity is much higher than the black of space and the resulting 'visible' discs (if you COULD seen one) are much smaller. I think this explains why something closer to Dawes is possible and does not require a Raleigh or larger object diameter.

In the image below, I have to be able to see through the PSF until it becomes brighter than anything superimposed on it - at that peak's (and only that peak's) visible threshold. If there is another bright one, so be it. They compete to be seen and you see both.

I know this is confusing, it's just a budding idea in my own mind, too. Again, Moltke holds a clue, as does Ganymede, as to why 'g' can be observed near the Dawes limit. It's a function of intensity of any one point and every other point near it than defines the limit of resolution - because we can see those points nearby. Even at Dawes, 'g' looked like a crater and not just a faint drop off in intensity. That bugs me.

Edited by Asbytec (02/24/14 05:37 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6393812 - 02/24/14 08:30 AM

Ok mulling this over - heading off to work.


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Re: Plato's challenge new [Re: Asbytec]
      #6393850 - 02/24/14 08:51 AM


Ok so since the moon in this case isn't providing the blackness of space for which to observe bright assemblage of airy disc points that firm features we see the narrow tips of these PSF's which are smaller in diameter allowing higher resolution than Raleigh or Dawes would suggest with their competitively swollen airy discs. Makes sense and this would explain Thomas' ball bearing views of details far below the R and D limits of seperation- again because the airy discs are not bright enough to show their full width height max. Ok.

I'm still not getting the spurious disc floating in moltke though.


Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6393909 - 02/24/14 09:41 AM

Pete, yes. The surrounding intensity defines the size of a visible disc of a brighter point (or series of points) such as a crater rim. Exactly. The black of space is devoid of intensity and allows the PSF to fall into blackness at it's full width at half maximum - the visual cutoff point after which all else is black. On the moon, this width is defined by the brighter surroundings with infinite point sources of it's own. So, the visible cutoff is much higher on the central peak intensity.

I have not worked out, yet, how the black crater pit doesn't allow a bright rim point to fall to FWHM. But the infinite number of points surrounding 'g' and inside the first minimum of a bright rim point (including the lack of points in it's pit) can only be seen if the points on the bright rim are transparent at some point. I can see the crater right "through" them because their intensity falls off enough and /maybe/ because they are smaller in diameter, too. Not much smaller, but small enough to allow something at Dawes to be seen "clearly" as a crater instead of a Dawes split with bright points and a fall off in contrast between them. I think...

Now, there is a fall off in contrast caused by a build up in intensity from the transparent parts of those infinite Airy discs surrounding the black crater pit. Not the rings, mind you. Those are out beyond the crater's diameter. So, it has to be a combination of very weak (otherwise transparent) intensity from each Airy disc bordering the crater. This means the brightest portions of those discs is small and the remainder out to the first minimum is transparent enough to see 'g' in crater form by looking right through them (since their first minimum is also larger than the crater diameter.)

Edit: I think this is why 'g' looked more like a nice crater as it did in Mike's image. Because the surrounding intensity was less and the area around 'g' (minus the bright rim) became an infinite number of equally less intense and smaller unresolved 'points' - of which we can only see the very tops of, so they actually are points. It's a smooth image like a crater in that sense, rather than a more crude "Dawes split" appearance it seems it should have been. However, the bright rim has to affect it somehow because it is brighter and somewhat larger in visible diameter. Still thinking this through.

On Moltke, the rim is a series of infinite bright points looped in a circle. Each of these points has a ring around it, which means energy inside and outside the ring - inside and outside that ring of bright points forming the rim. That bright spot in the middle is the convolution of all the inside energy combining in some unknown way - but in the same way it forms a diffraction ring along the outside of the rim...and along the limb of the moon, too, for that matter.

Edit: Okay, Moltke is 6.5km in diameter. Using the small angle formula, Moltke is 3.5" arc across at the moon's estimated distance of 382,000km on 6 Feb. From the rim to the center of the pit is ~1.8" arc. The first bright ring for an obstructed 150mm aperture is 1.61 lambda/D ~1.2" arc. So the inner diffraction artifact - the first ring, if there is one, should be just shy of half way (0.6" arc) into the crater pit. It's inconclusive that was what I was seeing. Maybe that's close enough. Something bright was there. Dunno what else it would have been if not an artifact. Rubble in its floor at that sun angle?

Make sense?

Edited by Asbytec (02/24/14 11:40 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6394869 - 02/24/14 07:38 PM

I don't think it'd produce a spot like that Norme. I see the convolution point as you explain it but I don't think it'd be visible like that or there'd be far more of these pseudo peaks arising. Two things come to mind:

Maybe there was afterall a stretch of sunshine on the floor. Moltke has no peak and is a smooth bowl of a crater at any resolution an amateur might make.

It could be a spurious brightening in the eye of the observer. This is a phenomena much like some times seeing the central star in m57 when it should be quite invisible for observer and OTA. The mind could be filling in the gap here. Trouble with suggesting this is it then offers a lever for doubters to pull in order to douse the claim with credibility issues. There's always going to be this segment of observers who will couch these opinions - afterall - we do it ourselves sometimes. Not to dilute your achievements here but this is a phenomenon that might hold here - or maybe not...

Still -

The spot would seem to make sense within a circular ring of light about a dark crater pit. Because its circular these rings which would even be invisible along a straight edged feature however compound in contrast as the circle overlaps them - hence forming a spot. My problem with this is it would be a fairly common thing then that would even be well documented by this point - particularly to the chagrin of lunar cartographers gone by who had already had their share of these kinds of problems brought up.

Curious thing. It distantly reminds me of Stanislas' drawing of Ganymede or a white disc a mile away he drew - I forget the particulars. A sketch anyway of a white disc with center spot with a wavering com centricity about it of central dot - ring-limb . Picture a very pale bullseye on a white disk. Stan stated these were edge effects created by diffraction . It looked like an irradiation spot - again, diffraction afterall. Perhaps that's what's at work here in an inverse way. I don't know.

A curious thing. Wish I were able to do a simultaneous on of this with you. Ehhh such is the 12,000 mile time difference!

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6394915 - 02/24/14 08:04 PM

I dunno what it was, Pete. I can only imagine at the right diameter a diffraction artifact might show inside the pit. Maybe not. I just don't know. Maybe it was an illusion that looked like a non existent central peak. I do not know why a diffraction artifact would NOT show up in the center. Since I do not see that central spot illusion in every dark pit and Moltke has no central peak, I thought diffraction was the best explanation.

In any case, the real treat of Moltke is the idea you can see light and shadow inside the diffraction artifacts. I could see shadow and bright rampart inside them. I think this is a clue as to why 'g' could be seen.

Edited by Asbytec (02/24/14 08:17 PM)


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Re: Plato's challenge new [Re: Asbytec]
      #6394981 - 02/24/14 08:35 PM

What's interesting here is that you could see something DARK through the pattern - meaning its at least translucent. If it were - only brighter makes it through the pattern - well then you'd say its opaque and the peak of brightness gas to be strong enough to make it through . With something DARK showing through then its a different ball game in that it isn't ALL about peak brightness coming through but the transparency or translucence allowing such a view.

My personal belief in these matters Norme is that for you to come to the bottom of it you have to artificially create these contrasts and manipulate them to glean the information you seek. Not that telescopic observation won't eventually get you there but if you could artificially create a crater and replicate what's happened here - and most importantly - manipulate it - you'd have your answers far sooner with a deeper understanding. My feelings anyway.

Perhaps a moltke mockup made of plaster of Paris - illuminated at night - make the crater an inch across - and use just your finder scope perhaps and see what budges. Make differing sized craters etc perhaps. Leave the plaster white - shadows will delineate form.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6395083 - 02/24/14 09:56 PM Attachment (6 downloads)

I thought to use the term translucent, too. But I do not think it fits. 'G' could be seen clearly in (very small) crater form albeit grayed out by diffracting effects - of the central peak intensity profile, not the diffraction rings. The central peak intensity has to be transparent and that means something in terms of seeing small light and dark features superimposed on the diffraction image. That has implications for 'resolution' limits.

Here's an artificial example of what I actually saw. It's an approximate illustration of the concepts. Note how you can see yellow (Plato's floor) points inside the Airy disc formed by a bright rim point. This should not be surprising because it's basically a double star problem. Now add an infinite number of 'companion' points of the same floor intensity and it begins to build up a clear image of 'g'.

Not just one, as in the case of a double star, but infinite number of them can be seen "through" the brightest point Airy disc - because that disc is transparent at some point. And that point - where nothing else is bright enough to show through - is much smaller than 'g' itself. In effect, it is opaque only because there is nothing brighter to be seen.

The green points are intended to show points of equal intensity as the edge of the brightest PSF, thereby defining the visible diameter of that bright point (much smaller than FWHM and a lack of light as in space.) I think this is what allows at least Dawes to be resolved on the moon in high res "picture perfect" form - not just a grey space between a bunch of bright ones. (Which it is, but not like we might envision a bright ring with a fall off in intensity in the middle. It was in picture perfect crater form.)

Also note how 'g' fits nicely into the Airy disc first minimum (dotted line) of every point on it's circumference. 'G' can be seen because each intensity is not only small, but beyond that small circle of (opaque intensity) the disc is also transparent. 'G' was almost photographic in appearance - not a crude Dawes split.

Yes, not only am I claiming 'g' was resolved, I am asserting emphatically, and without wavering, it was resolved in clear crater form. That's what bugs me. The bright rim was not bloated and blotting out the pit, it was pretty well defined. And it's edges were not noticeably blurred. They may have been, but on such a small feature it was just hard to notice well.

Edited by Asbytec (02/24/14 10:26 PM)


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Re: Plato's challenge new [Re: Asbytec]
      #6395232 - 02/24/14 11:24 PM

Arrrgghhh!!!!

This is confusing, even abstracting!!!!

I'm sorry Norme. I'm there with you on G and all but this illustration is making me cross eyed. Plus I'm tired.

And aggravated.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6395274 - 02/24/14 11:55 PM

Okay, 2 shots of rum later:

Hey it makes sense!

Yes it would seem that G and your Mak has the serendipity of the minima just outside it though - this is such new territory in a way I'm still unclear if having the minima straddle G would be pro or con.

Bottom line what's happening here is you got two extremes at work in opposite directions:

You've got the super high contrast moon with its severe light and shadow putting up an extended object you won't see anywhere else celestially. Doubles have their own rules and planetary doesn't begin to approach the values of light and dark that's here. I'm tempted to at the moon has its own res limits not transferable from other objects, ie: doublestars.

For all that though - look what's happening here. You have the stark FHWM
of airy discs whittled down to their peak intensity widths because the surrounding terrain on the moon is not too far behind it, ie: bright crater rim versus crater plains. Said anotherway - if all those infinite points were showing FHWM normally seen in stars your angular res would take a hit as the bloated points smoothed away the finer details. In doubles you don't get this resolution advantage because for the peak intensities to be small enough to show a finer separation they have to be so dim the eye grains out and its a case of diminishing returns. If that were not the case wed be getting these amazing sub arc sec splits on 14v doubles. But that's doubles. With the moon the higher angular resolution can be had because the lower intensity of peak brightness is made up for by so much lunar area of infinite points. Its a matter of more infinity LOL'!!! - versus the paltry infinity of a double!

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6395298 - 02/25/14 12:07 AM

I'm curious...

Ok we have G here with the first diffraction ring "serendipitously" outside it. I'm guessing then in bigger Moltke where the ring DID cross the craters center the convolution of all the rings (or confluence?) produced that spot?

Hmmm.

Pete


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Re: Plato's challenge new [Re: azure1961p]
      #6395538 - 02/25/14 04:44 AM Attachment (7 downloads)

Quote:

Doubles have their own rules and planetary doesn't begin to approach the values of light and dark that's here. I'm tempted to at the moon has its own res limits not transferable from other objects, ie: doublestars.



Actually, I believe doubles and extended object resolution is the same problem. With a double you normally have only one other point tucked in close. Whether the normally dimmer companion is seen or not might depend on it's intensity at some radius from the brighter primary point source. If it shows inside the Airy disc and very close (smaller than Dawes) to the primary, then it can be seen because the primary's PSF is transparent to the intense light of the companion.

On the moon you do not have one intense companion, you have an infinite number of them. Same problem multiplied by every infinite point observed within the Airy disc of a bright point - from a crater rim, for example.

This may not be the mechanics actually at work with infinite points of varying brightness forming a smooth image. But, it may be a way to think about it. It may be that points close together each diffract not only themselves but amplify and cancel with points nearby in a very complex way. It could be this effect that might diminish the diameter of a single point allowing greater resolution. There may be a completely different explanation, but the effect seems to be the same. Somehow the bright spurious discs do not blot out the crater's pit leaving an indistinct dark spot, but they do make it gray. The image is clearly a crater (observing 'g' at this level) and not a grey spot.

At FWHM, the radius of a 6th magnitude point source is about Lambda/D. That's about 0.68" arc for a 30% obstructed 150mm aperture. That 0.68" arc is almost exactly enough to completely cover 'g' at 0.72" arc. Add a few more points and you can see how the overlap would diminish the pit to a grey depression. Maybe an indistinct one.

Now, it could be points on the moon are not 6th magnitude and are somewhat dimmer putting up less intensity and smaller FWHM. That could account for it, if the change in FWHM is significant enough from a 6th magnitude star. Still, even if the less intense PSF and smaller FWHM ar half the diameter of 'g' we might still have something of a problem. Put another bright point opposite it and it's FWHM will meet the other in the center of the pit - likely - making it a gray depression, still. It may not be a clear image with just two opposing points, now add the infinite rest of them.

So I have to ask not why 'g' was seen - but why it was seen so clearly. And I still have not worked out why the PSF does not APPEAR to expand noticeably into the dark pit blotting it out like we might expect. The visible discs of each infinite point must be pretty small to give such a clear - almost picture perfect - image of such a tiny crater.

I dunno, I wish I could see it again. Right now would be nice. I only saw it three times for a brief time, grey pit and brighter rim. Very small, very fleeting - but seen regardless. But why? Why was this tiny feature not blotted out by the brighter terrain around it?

Yea, on Moltke, that's my guess. Need to observe some more craters (with bright rims) about twice the Raleigh limit in diameter to see if it forms a central diffraction artifact. It need to have a black pit, though. Should be plenty of targets near the terminator.

I guess this discussion is public, but it's just you and me chatting.

Edit: Why did it look like the image on the right and not on the left? That's what bugs me. I more than likely would not have called the image on the left crater form - maybe a white speck. But when you can see the floor...it looked like 'e' only smaller and much less frequently seen.

Edited by Asbytec (02/25/14 05:47 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6395608 - 02/25/14 06:46 AM

...

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Re: Plato's challenge new [Re: Sarkikos]
      #6395617 - 02/25/14 06:59 AM



Nothing to say? Argue? Clarify? Input? Too basic, too obvious? Too complex? No opinion, no experiences that might help? No knowledge to offer? Just boring stuff?

Is the brick to the head aimed at me, Mike? If it is an insult, maybe I'll just delete all my posts and find another forum where people actually talk instead of talking to myself and Pete.

Edited by Asbytec (02/25/14 07:08 AM)


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Re: Plato's challenge new [Re: Asbytec]
      #6395622 - 02/25/14 07:13 AM

No, the brick is aimed at my head!


Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6395705 - 02/25/14 08:26 AM

I can honestly say the discussion got a bit too complex for me. I was enjoying it till it went over my head. Not your fault, just my lack of experience with what you were going on about.

I had to go and download Virtual Moon Atlas so I could find Plato, (need to get some books) waiting for the Moon to start showing itself in the evenings again so I can try to see what I can see with my li'l scope


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Re: Plato's challenge new [Re: Rareth]
      #6395726 - 02/25/14 08:35 AM

I usually step aside and let the math, science, and optics gurus work out the technical aspects of observing. When they're finished - if they finish - I try to garner reasonable conclusions from their work in order to apply it to my own observations.

Maybe I'm just lazy. School is out!


Mike


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Re: Plato's challenge new [Re: Sarkikos]
      #6395756 - 02/25/14 08:59 AM

I'm just glad you guys are following along. Makes the effort worth it for me.

I find the observation both surprising and interesting. It's intriguing.

I don't have the mathematical prowess to express any kind of theory, or the equipment to experiment and test, or anything other than one fleeting empirical observation and some basic ideas of how it might work.


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Re: Plato's challenge new [Re: Asbytec]
      #6395763 - 02/25/14 09:00 AM

Yes, please continue the lesson. If I drift off in the back of the class, just throw a brick at me!


Mike


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Re: Plato's challenge new [Re: Asbytec]
      #6395766 - 02/25/14 09:02 AM

Quote:



Nothing to say? Argue? Clarify? Input? Too basic, too obvious? Too complex? No opinion, no experiences that might help? No knowledge to offer? Just boring stuff?

Is the brick to the head aimed at me, Mike? If it is an insult, maybe I'll just delete all my posts and find another forum where people actually talk instead of talking to myself and Pete.



I've given up posting images since the vast majority of the "discussion" just says "great pic" or equivalent even when it isn't.

Those who don't like mathematics, or anything with a detailed logical argument process, can ignore the threads that contain them. Brickbatting simply isn't called for, it's rude if not deliberately insulting. Free speech - people have a right to say what they think, even if you don't understand or agree with them.

Asbytec, please don't delete your posts & go elsewhere. At least some people appreciate them a very great deal.

BTW I know this post is off topic but placing it elsewhere would destroy the context. But can we now get back on topic, please?


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Re: Plato's challenge new [Re: brianb11213]
      #6395776 - 02/25/14 09:08 AM

Yea, Brian, I'm sorry for taking the greamlins wrong, I didn't understand them in context. I think Mike was expressing frustration. As I should.

I'm not going anywhere, just kind of quiet and lonely when it feels like you're talking to yourself and Pete. I came back into this forum after a grumpy encounter in another forum (entirely unrelated) with an insulting, ignorant commentator. My fault...I was defensive.

I'd still like to know what the pit was not blotted out or foreshortened by the points around it. Just gotta let the old subconscious mull it over until it hits me in the shower. Speaking of shower...

Edited by Asbytec (02/25/14 09:11 AM)


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Re: Plato's challenge new [Re: Sarkikos]
      #6395787 - 02/25/14 09:17 AM

Quote:

If I drift off in the back of the class...


Mike



Okay, hence the "snoozing" gremlin...dozing off in class. I thought it was expressing boredom with such a simple subject everybody but me understands. And the brick was for me because I don't.

Oh well...I kind of knew that was out of character for you, Mike. You've not picked on anyone I know of, "why me!"

SORRY...SORRY!


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Re: Plato's challenge new [Re: Asbytec]
      #6396859 - 02/25/14 06:52 PM

Hey Norme...

::


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Re: Plato's challenge new [Re: azure1961p]
      #6397026 - 02/25/14 08:13 PM

Pete...

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Re: Plato's challenge new [Re: Asbytec]
      #6397363 - 02/25/14 11:06 PM

So lets look at this ...

You are confident in the 5.5/D as I was with .32" Delta Equueli - its a THIN sighting to be sure - my standing elongation detection. Reason mentioned then is the following. When you do hit thes marks it kind of forecasts hypothetically what might be possible - or not. Vagaries of doublestar measures aside, Im forecasting a possible .28-.29" elongation based on the success of Delta E. with that claim (or wish rather) Id have to ask where you think 5.0 or 4.0/D might fit in with future attempts, seeing willing.

If you could shrink "G" down some in your head - how far would you go before you think it vanishes altogether ?

Pete
And yes this cabin fever is making me think about warm nights, sub arc second doubles and that hazy borderland between elongated and not.


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Re: Plato's challenge new [Re: azure1961p]
      #6397464 - 02/26/14 12:24 AM

Asbytec,

Don't go away. I always read your posts with great interest even when I don't understand the technical stuff.

Dark skies.

Jack


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Re: Plato's challenge new [Re: mountain monk]
      #6397680 - 02/26/14 05:44 AM

Jack, I got squared away. Happy now. Thank you, Sir.

Pete, right now 5.5/D seems like something near a diffraction limit, guessing from the fleetingness of 'g'. 9/D appears to be a practical limit for average conditions and sits well with my own experience with Plato at times.

However, 'g' was in crater form, so we might be able to push deeper. Since it rolled in and out - mostly out - even in the steadiest moments during pretty good seeing, I suspect it's getting close.

Still, it was the very good seeing itself that prevented holding it steady. Who knows, maybe if seeing were perfect for longer maybe something smaller could be seen. I would just have to witness it during those absolutely still, lab-like conditions to be sure.

At some point we're going to loose resolution. I am just not sure where that limit is. It's possible one might get even further down toward 4/D before loosing crater form, but it has to be observed to prove it. That's a tall order even in nearly perfect seeing.

Edited by Asbytec (02/26/14 05:50 AM)


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Re: Plato's challenge new [Re: azure1961p]
      #6397864 - 02/26/14 09:00 AM

Pete, just remembered I had a chance to go deeper than 'g' on that same night. Crater 'h' was right there in the FOV. I could tell it was there, but it was not in crater form nor was it elongated at that pretty darn good level of seeing. It seems elongation should have been easier, but I think the brighter rim between the two may have prevented any elongation from being detected. I cannot attest to their tiny width being glimpsed or even hinted at.

David's measurements for the diameter of a single component of 'h' are about 0.74 miles individually. So, at that level of excellent seeing, I was unable to observe crater form at 0.74 * 5.9 ~ 4.4/D. I mean not even a hint. (Well, I thought I saw a dark spot once, but most of the time is was just a jumbled mix of bright 'something' there.) So, at least in very good seeing (though not perfect lab-like seeing.) I'd think 4.4/D is too optimistic, at least empirically, for me on that night in that scope. So, I'd estimate the resolution limit to be at least 5.5/D having observed 'g' (0.9 miles), but not quite down to 4.4/D (0.74 miles.) Maybe a tad less than 5.5/D on the best nights. I might guess the absolute limit (diffraction and seeing) is just about 0.85 miles in diameter at the lunar distance that night.

So, using the small angle formula (distance 250,000 miles and diameter 0.85 miles), I'd wager a 150mm can do 0.70" arc. As David mentioned, Dawes is calculated at 0.77" arc. Taking the obstruction into account one might get there if the atmosphere were perfectly steady and everything else was textbook, too. (0.77" arc * 1-co^2 = 0.70" arc.) I guess it's really no longer at Dawes per 115.7/Dmm, but effectively a obstruction modified Dawes limit.

Resolution to 0.70" seems to fit with theory pretty well, if one could actually see a crater at 0.70" arc. Pretty impressive if it can be done, but all variables need to be perfect. If a mosquito buzzes through the light path, forget it.

Here's the thing. I think a 6" is a sweet spot, at least here. Seeing is often (but apparently only very close to) diffraction limited. That should be about 8/10 on the standard scale. And I get 8/10 fairly often, if just in spurts. So, if it's 8/10 or better, resolution seems possible on those scales even if only fleetingly. Larger apertures will have a bit more difficulty reaching the diffraction limit even in our local conditions. So, resolution may not be strictly down to ~5/D as seeing begins to dominate larger apertures.

Sure, their resolution is higher and they can see smaller craters, but maybe not down to 5/D because seeing is dominate most of the time. If larger apertures can get 5/D, it would be in a very rare moment of perfect seeing for that aperture. The larger the aperture, the more rare those moments.

Imaging can capture those best moments, yea? That explains why Mike was able to nail craters to 5.5/D...at least the smallest one I picked out and measured as accurately as possible. (Gonna look at his image again for a smaller resolved crater.) And since 5.5/D is consistent with the best estimates of my observation of 'g' during the best moments in excellent seeing - rarely better - I'd think 5.5/D could be a RoT near max resolution on the best nights. Maybe deeper, but not very much and also very rarely so.

But, I've been wrong before.


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Re: Plato's challenge new [Re: azure1961p]
      #6397917 - 02/26/14 09:33 AM

Quote:

Hey Norme...

::




Now I get it!


Mike


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Re: Plato's challenge new [Re: Asbytec]
      #6397950 - 02/26/14 09:50 AM Attachment (15 downloads)

In Mike's image, there is a tiny crater that does show a tiny, gentle crater form just west of 'm'. According to quickmap, it is about 450m across. It may be a tad larger. But, at 450m (0.28 miles) that does equate to 0.28 * 18" ~ 5/D.

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Re: Plato's challenge new [Re: Sarkikos]
      #6397960 - 02/26/14 09:52 AM

Oh, there you are!

Oh, I forgot to yell, "DUCK!"


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Re: Plato's challenge new [Re: Asbytec]
      #6398183 - 02/26/14 12:00 PM

Quote:

In Mike's image, there is a tiny crater that does show a tiny, gentle crater form just west of 'm'. According to quickmap, it is about 450m across. It may be a tad larger. But, at 450m (0.28 miles) that does equate