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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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Asbytec
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Re: Plato's challenge new [Re: edosaurusrex]
      #6317564 - 01/16/14 10:36 PM Attachment (21 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 (23 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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OrlandoMatt
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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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OrlandoMatt
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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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Mare Nectaris
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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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Asbytec
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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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