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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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Mare Nectaris
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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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Asbytec
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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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Sarkikos
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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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Asbytec
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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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azure1961p
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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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azure1961p
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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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Mare Nectaris
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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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azure1961p
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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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Asbytec
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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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azure1961p
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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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Asbytec
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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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David Knisely
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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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brianb11213
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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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David Gray
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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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azure1961p
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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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Asbytec
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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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