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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5542888 - 11/27/12 09:40 PM

You have a stationary floater nearly on axis. That's weird, mine shift all the time. Sometimes pretty clear, other times that big annoying one that rides on axis for a while. But, I can get them to scurry around by flicking my eye. Then there is a small clear window to observe though as they scurry about. The next night that offender is nowhere to be seen.

Doing the math last night in my head, and wagging it while half asleep, I figure the spurious discs on Io should be about the same size as a 6th magnitude spurious disc in a 150mm unobstructed scope. A little larger because it's brighter, then smaller a bit due to the CO. Anyway, the spurious discs formed on Io should be smaller than Io itself, at least currently.

So, if that is true (I believe it is), then at least one spurious disc on the eastern limb could be seen as elongated from one on the western limb. And, of course, with many more between. This would hold true for one on the northern limb elongated from one on the south. And, if they are a bit less bright, they may appear darker even if overlapped by some brighter ones along Io's equator.

It would be much like observing 72 Pegasi where the companion is in tight but a tad fainter (~5.7 and 6.1, respectively.) And elongation was visible with the fainter companion as a hump on the companion's disc at just 0.5" arc. That's smaller than the separation at Io's equator (and poles.) And that separation is tighter than the Sparrow limit at 107/Dmm. But there was no contrast between the spurious disc centers, just elongation (very evident in the diffraction ring) and a slightly fainter "hump."

Trick is, are Io's poles darker by enough to be detected as being dimmer than it's equator, hence some elongation effect? That get's complicated with numerous spurious discs superimposed on one another, unlike the two easily elongated by 72 Pegasi. Observing Io might be like separating two 5th mag stars separated by Io's diameter: two 5th mag stars at 1.2" arc. Bright when PA is along the equator, and dimmer from pole to pole at that same separation. At that mag and sep, it would be like splitting 32 Ori (slightly unequal pair at ~1.2" arc) with no dark space, of course. It is obscured by other points.

Processed and enhanced images show pole darkening quite easily, they eye not so. Hence the PITA you and I have calling it elongated. But, again, I think it's doable in 6" and 8" apertures based on the math and reports observing elongation - or hints of it. Not easy by any stretch, but Eddgie could do it with a higher degree of certainty.

Edited by Asbytec (11/27/12 09:45 PM)


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sqrlman
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5548877 - 12/01/12 02:16 PM

Some years ago I was observing Jupiter with my C8. With no prior knowledge of any events I noticed something odd. It looked like an equals (=) sign on one of the bright zones. I kept watching it and then I noticed it was moving. This was Io in transit. The bright areas of Io become invisible when it's crossing a bright zone and the darker poles now stand out. Interesting to see.

Steve


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stray1
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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5549774 - 12/02/12 03:16 AM

During my evening walks I listen to Astronomy Cast on my MP3 player. Since I have taken an interest in Jupiter as of late two of my recent downloads have been "Jupiter" and "Jupiter's Moons". According to Dr. Pamela Gay, Io is basically a seething caldron of volcanic activity--a lot of lava flow and sulfur gas emission, especially in the equatorial region (caused by the gravitational pull of the gas giant). The poles, while active, are much less so.

I'm thinking that the elongation effect might be caused by sunlight reflecting on gas along Io's equator. Looking at the photo that Norme posted we can see that while the moon appears elongated, its shadow does not. This effect would probably be apparent whether Io was in transit or not...maybe...possibly...?



-stray-


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: stray1]
      #5549806 - 12/02/12 04:46 AM

Quote:

This effect would probably be apparent whether Io was in transit or not...maybe...possibly...?



-stray-




Don't be confused, it just might.

Personally, I found having something comparable in size that is known to be spherical for comparison introduced a small bit of doubt about Io being circular or spherical. The shadow might serve that purpose. Callisto was in the same FOV for comparison before Io transited. That was very convenient, but not conclusive.

It was a very tight call with Io against the black of space even with Callisto nearby. Over the cloud tops, it was more convincing. It really did take on a tiny bit of a bright dash-like appearance, whether exclusionary or not. It was still very hard to say for sure. I'm convinced it's more readily doable in greater apertures, even against the black of space.

Fascinating stuff.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5549941 - 12/02/12 08:52 AM

This is an engaging speculation. I really want to pursue it.
Pete


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5550248 - 12/02/12 12:17 PM

Quote:

This is an engaging speculation. I really want to pursue it.
Pete




Speculation just ended for me, Pete, on Dec 2 at 1700UT. Ganymede, Io, and Europa all in a row trailing Jupiter on the Zenith in 9/10 seeing and 384x - all three in the same FOV.

Ganymede is easy to ID, I actually picked Io out of the line up because Europa was perfectly circular. Io was not. I would never have believed such a thing until my lying eyes showed it to be true. It can most certainly be done.


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stray1
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5551400 - 12/03/12 02:19 AM

I did a little deeper research on this topic and I think that the elongation that you guys are observing might be a result of Io’s constant volcanism (apparently the most active in the solar system) and that Jupiter’s magnetic field is perpetually stripping away and absorbing the moon’s temporary, though constantly replenished, sulfur dioxide atmosphere.

One interesting thing that I read on Wikipedia (link below) is [that] “…this material escapes Io's gravitational pull and goes into orbit around Jupiter…these particles spread out from Io to form a banana-shaped, neutral cloud that can reach as far as 6 Jovian radii from Io, either inside Io's orbit and ahead of the satellite or outside Io's orbit and behind the satellite”. I’m certainly no expert on this topic, but this “might” explain it?

I’m wondering if I can see this effect through my 90mm (f/ 910) using a 6mm EP and a x2 Barlow. That would give me what…303x?

http://en.wikipedia.org/wiki/Io_(moon)#Interaction_with_Jupiter.27s_magnetosp...


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: stray1]
      #5551592 - 12/03/12 07:19 AM Attachment (22 downloads)

Hi, Stray, will read your link in a moment. Just wanted to post a sketch from last night, during opposition.

Ganymede seemed to sport a slightly less bright Jupiter-side limb. It might show in the sketch. No bright specks noted. Callisto is really more "beaver" color. Yes, that's a color very close to a grey brown. (Beaver #9F8170 R62%, G51%, B44%.)

http://en.wikipedia.org/wiki/List_of_colors

Europa was strikingly yellow with a faint distinct diffraction ring. Io was more orange with a hint of reddish. It also sported a fain diffraction ring. But, here's the thing. Europa was distinctly circular, Io is not. In fact, it's diffraction ring was slightly distended.

I tried to capture as accurately as possible that difference. Seeing during opposition was 9/10 and Jupiter was on the zenith around 1630UT. This sketch represents about 1630UT, but leaves Jupiter as it was at 1430UT and only for reference to simulate the view.

Edited by Asbytec (12/03/12 07:33 AM)


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5551640 - 12/03/12 08:26 AM Attachment (24 downloads)

A better look...

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Rich (RLTYS)Moderator
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5551674 - 12/03/12 08:53 AM

Cool looking.

Rich (RLTYS)


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5552300 - 12/03/12 03:42 PM

It is perfectly circular.

In the C14, I see it as distinctly circular. What I observed though is that there appears to be some albedo darkening at the north and south.

In a small scope, I think you are basically just getting some diffraction blurring of the central "strip" so that it is "Stretching" the central band.

I may have trouble describing this, but let me give it a try.

Suppose you have four or five Airy Disks in a line with the edges slightly overlapping. At the top and bottom of this "Bar" the light from the diffraction will tend slightly fatten this bar so that it will appear slighly wider than it is.

At the end of this bar though, the light will appear to make the bar stretch slightly.

Because in smaller scopes, the central part of Io's disk is only maybe a few Airy Disk diameters, you can see how a brighter equitorial region with darker northern and southern hemispheres could start to look almost like a football.

But in the C14, it looks very circular. I see albedo darkening at the hemispheres, but it still appears circular.

The effect though, contributes to the "Pearl" appearance. It is like there is a luster to the circle.

But it does appear like a circle. Diffraction I think could make it look more like a "Dash" in a smaller instrument.

If one wants to bother to compute the Airy Disk and firt ring diameter of their scope and super-impose these over the center of Io, I think you would see that Io only appears a few Airy Disk diameters wide, and a bright diffraction ring at either side would then show the "elongation.".


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5552574 - 12/03/12 06:40 PM

Eddgie, makes sense. I suspect you are correct, Io is indeed circular in larger apertures. I just could not "resolve" the polar albedo as you could. So, yes, the overlapping /spurious/ discs would tend to elongate Io in smaller apertures. One can easily imagine a C14 would better resolve Io showing even the polar regions giving it a circular appearance with a brighter equatorial region. One might argue that's more true resolution.

In a 6", Io at 1.7" is just a bit smaller than the Airy disc diameter (1.82") but also nearly twice the diameter of the (series of) spurious disc(s) at Io's magnitude with the CO considered. The combined diffraction rings would sum into a slightly elongated first ring much like a brighter, very close double of equal magnitude (72 Pegasi at 0.5" arc, for example.) It might be that the dimmer poles contribute less to the diffraction ring observed.

The idea Io simply "appeared" elongated, even though it is not, is perfectly sensible. While not true resolution in the Raleigh or Dawes sense, maybe the lack of observable polar spurious discs could be considered resolution in much the same way Cassini is resolved through lack of any light emitted from it while the brighter bordering regions offer such diffraction.

It is a stunning revelation, none-the-less. Never would have thunk it possible to see such variation in Jovian moons we normally think as simply "discs." Never would have had reason to believe otherwise until this thread.


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5552734 - 12/03/12 08:11 PM

An afterthought on Io's color. Reading Stray's article above, Io is sulfur and silicates, and high res images show a distinct yellow color. That actually confuses me, because I found Io to be more orange-slightly red and Europa to be yellow. Io's poles, apparently, are more orange than it's yellow equator. And I do no think I am seeing much light from the poles.

So, why is it orange? Not sure. In fact, that night observing the moons, I made the initial ID on Io based not on it's color, but that it was (indeed, appeared to be) more elongated than the yellow one further east. The red, elongated one had to be Io, and indeed it was. That, itself, was stunning.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5552755 - 12/03/12 08:22 PM

I'm getting what Eddgie is saying and its what I guess would be the case and yes Io is truly round afterall but the meat and potatoes here is that this is a heretofore unheard of achievement in detection and resolution with a 6" aperture. Time waswhen the four moon's of Jupiter written about in books were noted on magnitude difference and by the way the shuttled around back and fourth. They were treated as ornamental things framing a more worthy object and that was that. Then it became written about that they could be resolved as discs and so that added something in the guidebooks. Beyond that some shadings were mentioned ad visible in only the larger Scopes and anyway Jupiter is the main subject so moving on. .. then some time in the 90s Gary T. Nowak of Vermont's Astronomical Society turns his ten inch Trischiefspeigler on Ganymede with the sole purpose of going out on a limb and looking for detail inwhats normally big scope territory. He sees the detail then goes a step further and even manages with a 6" apo. He notifies Alan MacRobert at Sky and Telescope who realizes the gravity of the achievement and publishes Nowaks finds. Gary redefined what the limits were. For having a visa to detect albedo shading and I for one NEVER looked the same way at the moons in general again. What's happened here is the next progressive step and it wad wild to see it unfold and so unassumingly. I truly wrote this off as seeing related.

Someone ought to pass this on to Gary.

Great stuff.

Pete


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5552974 - 12/03/12 10:16 PM

Well, I think amateurs have been reporting seeing albedo features on Ganymede using 6" instruments for many years. I know I have seen them in 6" refractors from time to time.

And I have done much better than this on Ganymede with the C14, having resolved Osiris and Galilee Regio as distict shaped features, and I know this has been duplicated by one European observer using an 8" APO.

Io is much harder though. There have been several good C14 images that show very clearly resolved surface structure, but visually this is very difficult. I have seen shadings hinting at structure on Io, but not what I would call "resolved features."

I think that it is good that people are reporting these things because it will encourage others to look.

But Norme I think has "the right stuff."

The "Right stuff" is patience and persistance.

I feel like I have done some very excellent observations too, and patience and persistance have been the most important tools... More important than what eyepiece you use for sure.

I often observe Jupiter for up to an hour waiting for moments of good seeing. And a funny thing happens... In moments of good seeing, your eye will catch a detail. A few minutes later, your eye will catch another detail.. And your brian I think starts "Building" a picture. And suddenly, even though seeing is not really any better, it seems like you are now seeing a lot of the detail that previously was difficult.

Some people refer to this as "Mental Stacking" and I am a believer in this description.

People should look. Even if conditions are not great, they should get comfortable and keep their eyes open (I binoview.. LOL). And with patience and dedication, it happens.


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5553083 - 12/03/12 11:20 PM

Eddgie is correct, partially, persistence is important. His own observations as does Jason's persistence resulting in this thread attest to that. Most of our observations require persistence, patients, and a desire to observe awesome and powerful natural beauty of places we cannot visit. And that Eddgie and Jason all report Io sightings is ground breaking fro amateur visual observing.

Observing is one thing, equally important is people like Pete pushing back the observing boundaries we read about in books. Forget Dawes, forget even Sparrow, go deeper and you will be surprised. He is absolutely correct. I never would have attempted 72 Pegasi at less than the Sparrow limit nor a myriad of other unheard of observations. Pete pushes the real telescope limits well into the realm where seeing sub arc second is required.

And that's the point, some observations are unheard of. I think it's absolutely wonderful guys are out observing such things and describing the universe we live in. Pete tells the story above like no other, we all know the Galilean moons are discs. We've know that for years and have been just a little bit wrong. Now we are telling a different story, one that says go and look at them. Sure, folks have been reporting albedo on Ganymede for years, but everyone should do it. It should be in all the observing books. It adds to the beauty of our observing.

For me, the right stuff could not be more right. Persistence and patients, desire, attention to detail, and folks like Pete driving it even deeper and all that under some excellent skies with a scope that is finely tuned and in it's niche`. It really get's no better, except maybe with some aperture.

Eddgie, mental stacking is how my sketches develop over time. Catch a detail here, then one there. Before long the entire NEB is rife with light and dark shading and dotted lines. There are times when Jupiter just "burns" into the retina. It really does look like an image (minus the finer features.) In those moments, color is much more pronounced and the detail is just "pencil dropping." It lands right next to your jaw.


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sqrlman
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5553610 - 12/04/12 09:18 AM

Quote:


In a 6", Io at 1.7" is just a bit smaller than the Airy disc diameter (1.82") but also nearly twice the diameter of the (series of) spurious disc(s) at Io's magnitude with the CO considered. The combined diffraction rings would sum into a slightly elongated first ring much like a brighter, very close double of equal magnitude (72 Pegasi at 0.5" arc, for example.) It might be that the dimmer poles contribute less to the diffraction ring observed.

The idea Io simply "appeared" elongated, even though it is not, is perfectly sensible.





Io is in fact only 1.2 arcsec currently. What is sensible here? Is it logical that a smaller telescope can show something elongated that isn't elongated?

Steve


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5553669 - 12/04/12 10:05 AM

Io is indeed 1.2" currently.

Io's colouring is not uniform. It is darker at the poles than at the equator. During transit, to me, it does appear to be elongated, squashed pole-to-pole, if you will. When not in transit, it appears to be a perfect disk.

I suspect that the poles are very close in albedo to the Jovian cloud band behind it, and thus are not resolved due to lack of contrast. I suspect that the bright equatorial region is resolved, as it has higher contrast with the background clouds than do the poles. It seems reasonable to me that a larger telescope might well be able to resolve those poles, returning Io's aspect to circular in the more capable instrument.

If a 1.2" disk can be resolved as a disk (and Io, to me, presents a clearly circular disk when not in transit), then it seems reasonable to me that a feature that is 1.2" by 1.0" (for example), might well be resolved as a non-circular disk. I believe this is the case for Io's equatorial region while in transit.

The effect is VERY well shown in many astrophotos of Io in transit, taken by scopes in the size range discussed. I guess that makes the question into one comparing the spacial and contrast resolutions of CCD's vs the practiced human eye.

I question the validity of my own observation. That was the purpose of this thread, to explore the possibilities of what I think I have seen. At least a couple other members have effectively duplicated my observation, from reading above. In beginning this thread, I'd have called my confidence in my observation at about 65%. I'd raise that now to 80% based on the reports of Norme and others here, though weather has prevented me from duplicating my observation.

I've very much enjoyed the discussion thus far.

J


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5553693 - 12/04/12 10:21 AM

Yes, possible.

An extended image is (in theory) made up of an infinite number of overlapping Airy Disks.

They are not laid "Edge to edge" as in my clumsy attempt to describe what I think may be at play but rather very slighly overlapping.

If the planet were perfectly illuminated, diffraction would make the planet look perfectly round.

But diffraction has this quality. A black line between two white lines will appear narrower because the light from the bright lines will diffract into the black line at either edge.

But a white line between two black lines will appear wider, again because the light is diffracting over the white dark lines.

I can see that there is albedo darkening on Io when conditions permit. I reported this in a post a couple of weeks ago when I reported that Io looked like a domed rivet in front of Jupiter when viewing a transit. I suggested that this and the pearl like look were a result of slight albedo effects.

And images show it clearly.

If there is a brighter equitorial region, and a darker limb on either side of that, then I think diffraction could indeed permit a 6" instrument to see that the "Length" of the "Line" (the brighter equitorial region) could appear to be stretched out because the very edges where the limb was darker would taper off before the ends of the line.

The result would be like maybe two very slightly displaced Airy Disks, which would indeed appear lengthend.

And this is exactly what a Sparrow Criterion spit is. There is not actual split, but becuse the Airy disks overlap but are not perfectly concentric, the elongation may be just sufficent to see the combined stars as something other than a singel point source.

And Io could be doing the same time. The theoretical Airy Disk "Pixel" on one end of the brightened region and the "Pixel" on the other end of the brightend region both generate Airy Disks that are seperated by 1.2 Arc Seconds (the width of Io's Disk). Now, you have two Airy disks that are spreat at the edge by this amount.

If the source were unevenely illuminated, being darker on one side and the other than at the center, then using the powers Norme is using, I think that it would be enough to perceive a very very tiny lengthening.

Again, recent images clearly show strong albedo and even surface resolution on Io, and I have seen albedo differences visually in the C14, so there is proof and there is at least one visual observation that supports the uneven illumination.

So, I think that theory would support that this effect could occur, and the fact that at least two people using similar apertures have reported it(6" and 8") seems conclusive to me personally.

But I see skeptisim on this forum from time to time (Banding on Uranus, yea or nay?) but I see people making observations that I have made using larger instruments that I think might within the reach of their own instruments.

And I think this is the case here. I think it is within reach of Normes instrument.

But he and I had a variation on this conversation in the past.

I suggested that to see albedo features was different than having "Resolved" a detail, and this is a great example (and one that I think may cause him to re-evaluate our previous conversation).

In this contect, I think Norme has "detected" that there must be some shading on Io. Otherwise Io would be perfectly circular (as it is in my C14). I can see though that there is distinct albedo shading. He can only "Infer" it because of the diffraction making the disk appear slightly elongated.

But that doesn't at all distract from the observation. In fact it stands in stark testominy to the laws of physics, resolution, and contrast transfer. As the aperture increases, the scope will have a better chance of showing direct evidence of uneven illumination, but the smaller apertue might only show an effect that could be described and attributed to diffraction effects caused by viewing an unevenly illuminated extended object.

Bottom line? I think it is a slam dunk.. He says he saw it, I know it is there (the albedo shading), and diffraction can explain it.


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5553737 - 12/04/12 10:48 AM

You're correct, according to JPL sim it is 1.2" arc. That's probably accurate enough for all intents and purposes. And in fact, I am trying to make sense of it myself through studying extended object diffraction. I offered one possible explanation above. If you have a better explanation, I'm all ears.

The power of suggestion can be pretty powerful tool. Was it suggestion that ruled the observation? It's possible, especially for those with a healthy dose of skepticism. Nothing wrong with that. But, don't let skepticism rule out attempting the observation, as crazy as it sounds. It's probably going to depend greatly on seeing, but there are always those good moments.

So, can a 6" do it. I believe it can, having actually undertaken the observation in nearly perfect seeing, cooled and perfectly collimated. And the timing could not have been better, at opposition no less. All the advantages were in favor of a successful attempt. If it could be done, the conditions on or about Dec 2 were ideal for attempting it.

Personally, I am no longer restrained by Dawes or Raleigh limits because of experience with point sources smaller and tighter than even Sparrow. A 6" can easily elongate 72 Pegasi at 0.5" arc and well below the Sparrow limit. So, because this violates Raleigh in a big way, and Dawes pretty much the same, neither in any way invalidates seeing something that tiny - to the best of my knowledge and recent experience.

The whole idea is to get others to attempt it, to validate and repeat the claim, or to refute it. You game? I feel you might actually be surprised. It's not like we're looking at something in the microwave frequencies, it's all visible light observation of an extended object. But, if there is an explanation as to why this is impossible, again I am all ears.

My cheese might well have slipped off my cracker and I would have no way of knowing it without someone stating so clearly. Or sending the white van to pick me up. But, until being absolutely insane is proven, I saw what I saw. And would have never believed it, either.

If it were not for Pete pushing back the theoretical, textbook limits and Jason suspecting something was strange with Io, I would have been busily humming along in life conversing with my invisible friend. Look, I really think there is something to the observation, and would urge anyone interested to see for themselves.

I just cannot get two images out of my head. One was a couple nights earlier when Io was approaching the preceding limb. I cranked up the power and looked at it. It certainly struck me as a tiny, bright dash mark. The second time, I identified Io immediately because it just did not appear right. I had two moons in the FOV to choose from, Io and Europa. I identified Europa because it was a perfectly circular disc. The other, less that perfect disc was Io. The color confirmed it, and so did every other source. It was Europa furthest out and Io next one in. That convinced me I am not nuts, or that I am...can't remember.

So, what's sensible? Well, what is not?


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