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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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Mare Nectaris
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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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Asbytec
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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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photonovore
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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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Asbytec
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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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David Knisely
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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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David Knisely
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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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Asbytec
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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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