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JasonBurry
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Some thoughts on a Transit of Io
      #5540082 - 11/26/12 10:55 AM

Friday night brought about 30% clouds, mediocre transparancy and quite good seeing, along with a 20km wind and unusually warm (+9C at 11pm) temperatures. After supper, I set out my 8" dob and my 4.5" newt and started them cooling. In 10 years of observing, somehow I'd never actually caught a Jovian moon in transit, and this was to be the night.

I did the bulk of the observing with my 8", the 4.5 was just there because the transit would be a fun test of its contrast and resolving abilities, with its near-spherical primary.... The 8" dob was running a 12.5mm plossl and 2x barlow, for about 200x. The 4.5" had a 4mm Huygens of very low quality, giving 225x.

The GRS turned out of view a little before Io's shadow contacted Jupiter's disk. The seeing was uncommonly good, with all 4 of the moons showing clean disks, with a faint spray of glare around each. Knowing Io's angular dimension, the seeing was generally well under 1".

As the shadow bit Jupiter's limb, I was astounded by the "3d-ness" of the spectacle. Fascenating to see the limb reach around the back side of the shadow, until it was a black spot on Jupiter's face rather than the bite it had been moments before. A look through the 4.5" newt showed the shadow quite well too, not quite so vividly, but easily observable. An pleasing view, when the planet was well centered in the FOV, as the cheap eyepiece had tons of false colour off-axis.

The real magic hadn't yet begun, however. Back to the 8". As Io approached Jove's limb, it seemed to take on a 3d aspect in its own right, a yellowish pearl. Its glide into the face of Jupiter's disk was astounding.... I was surprised how clearly the tiny disk stood out from the otherwise similar colourscape of the Jovian cloudtops. I was also able to see Io's disk in transit thru the 4.5" scope, but it was much harder to resolve.

Over the next hour or so, I began to notice something very peculiar about Io, and it is this that is the real subject of this post.

Now, Io has a diameter in the 1.5" range (I don't have the figure here), and an 8" scope has a resolution on the order of 0.5".

I could swear that in my telescope, while in transit, Io appeared to be elongated in the equatorial direction. It was my impression that it appeared to be about 3:2, seemingly squashed pole to pole.

Now I know that Io's effectively spherical. I also have read (in the imaging forum), that Io often appears "football" shaped in their images, aparently due to albedo (seems Io's poles are darker, and blend into the Jovian cloudtops more).

So, did I genuinely see this effect, or am I (once again, LOL) a victim of the "aperature of my own mind"? I was aware of this effect (the "Io Football") before I made my observation, but one cannot put the genie back into the bottle.

Anyway, it was a great blast watching the first half of this transit (before the skies went to pot), and one of the more memorable sights I've seen thru my scopes. What a beautiful season this has been for Jupiter. I've never seen it like this!

J


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5540227 - 11/26/12 12:22 PM Attachment (74 downloads)

First off, thank you for the fascinating account of a typical, yet magical, Jovian transit.

If the football effect is visible to the human eye, contrast wise, then you very well could have seen it. As to whether you are engaged in "aperture of the mind" or not, I have no way of knowing without evaluating your response to some ink blots.

That you know of the effect or not may not matter. Question is, did you see the elongation or not? You'll have to tell us. I don't know, but judging from the highly processed, yet distinct contrast, it looks doable under very good conditions necessary on that scale - IMO.

Quote:

What a beautiful season this has been for Jupiter. I've never seen it like this!




So true.

Edit: Sorry, image credit goes to...
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5520980/Main...

Edited by Asbytec (11/26/12 12:23 PM)


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5540245 - 11/26/12 12:36 PM

Yes, that image matches what I believe I saw, a very similar elongation of Io's brightness on the face of Jupiter.

I tend to think I DID see it...

Does that make it my first successfull detection of a surface feature (ie the dark poles of Io) on a Jovian satellite? I'm gonna contend that it does!

J


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5540278 - 11/26/12 01:06 PM

You know, that's an amazing feat. Pete was asking recently about any success on Galilean moons other than Ganymede. Here's one potential observation for him to chime in on.

It would be interesting to know more about the surface of Io. Does it indeed have darker poles? Or is it some sort of effect caused by uneven illumination of a sphere. Or is it an image processing effect? (I hope not.)

Again, just accounting for the image above, the contrast between the poles and the equator looks significant. Possibly enough to differentiate visually. But, maybe another observation or two would confirm it. Or if you held the elongation for a period of time, then it seems more real.

Another question that just popped up, does Io exhibit the same football effect against the black of space. If so, or if not, what does the answer mean? Does this effect require Jovian could tops to pull off. And if so, what does THAT mean? Are there images of Io against the black of space that show this pole darkening? Or is the pole darkening simply an "effect" requiring a Jovian backdrop.

In any case, it's a stunning observation. I am inclined to believe, if you saw elongation...well, then you saw elongation. I've never seen it, but I have never tried. Maybe I should, others should.

http://www.spacetelescope.org/images/opo9913c/


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5540370 - 11/26/12 02:04 PM

I'd observed the transit for an hour or so, from when Io first broached Jupiter's limb. I began to notice the elongation a few minutes after it was fully inside the planet's disk, and noted it repeatedly (I was bouncing from my 8" to my 4.5", but only noted this in my 8") over the first half hour/45 minutes of the transit.

Once Io had made it about 1/4 of the way across the disk, I went inside for a bit, and put away the 4.5" instrument. An hour or so later, when I returned to the eyepiece, Io was nearly halfway across the planet's disk, and much more difficult to resolve against the clouds. The seeing had deteriorated, the wind was rising and the clouds were thickening.

Just looking at some HST images of Io, and the poles do seem to be subtly darker than the equatorial region in many photos. I'd guess that what I may have observed might be a subtle colouring difference between the poles and equator that is all but blown away from my eye when seen against the blackness of space. But Io and Jupiter's colours are quite similar, so against the giant's disk, the more subtle detail in Io is more easily noted.

Or, I'm a victim (again) of the complex interaction between eye and brain. It's easy to have an idea in one's head, and to force the "eye" to see supporting evidence. I'm not sure if I saw what I saw or not, but I'm certainly gonna try to repeat the observation.

J


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MikeBOKC
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5540405 - 11/26/12 02:21 PM

Well Io is the closest large moon to Jupiter and the tidal forces on it from Jupiter's massive gravity are said to be responsible for the sulphur volcanoes detected by Voyager. Those forces would almost certanly also pull the planet's mass into a somewhat elliptical (vs. spherical) shape, would they not? Not that it is visibly an actual football shape, but even a minor aberration from a sphere might be exaggerated in certain views, just as the moon or Jupiter itself can appear squat and out-of-round when viewed low in the earth's atmosphere.

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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5540496 - 11/26/12 03:17 PM

Quote:

a yellowish pearl.




This is almost exactly how I described Io during the night about two weeks agon when Ios shadow transited the GRS. I saw Io as a pale pearl. Interesting that we both came up with the same analogy, but like you, I found that the similarity was striking!

And in that post, I attributed it to some very slight albedo effects!

And I noted the exact same oblate-ness but again, felt that both the pearl texture and the oblate appearance were due to albedo features on Io.

Anyway, I am of course quite sure that they would be visible to you.. I was using a C14 but my seeing was not great that night, so with better seeing it would not at all be a surprise to have someone report this using an 8" aperture.

And yes, the shadow transits have been great. Norme caught on where the shadow was on the Oval BA, and there have been images of both of these events.

Looking at images posted on CN though you can see that Io is indeed showing albedo features in most of the images these day.

But the "Pearl" analogy is again exactly what I reported, so that says that the effect is very real and more than ust an "Impression." When two different observers on two different nights use the same term to describe it, that kind of says that it isn't their imagination.

Nice report.


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5540515 - 11/26/12 03:26 PM

Eddgie, I read your report, LOL. Suspect that's what planted that "pearl" into my mind... It seemed hokey when I'd read it, but upon seeing it with my own eye, I might well have actually exclaimed something audible...

"By the gods, it does look like a pearl!"

J


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5540989 - 11/26/12 08:33 PM

Well, we're all a victim of our senses, our perception is reality. I wish I had a cold, impartial computer-like detection and interpretation of the world. Ah, no I don't.

It's interesting, however, that Io is football shaped against the planet. Thinking out loud, it if has the same color scheme, more or less, it might appear camouflaged against Jupiter except for it's brightness.

Could be volcanic activity that gives Io it's perceivable contrast. It probably does look pearl-like. Need to observe it more closely.

Hmmm...


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5541144 - 11/26/12 09:58 PM

Well, worse case then it is good to have someone else "Confirm" my report that Io did not look like a simple bright disk against the Jovian clouds.

But I am thrilled that someone else not only enjoyed the sight the way I did, but agreed that the "Pearl" look I reported was in fact visiable.

Very happy that you saw it and reported it....

Cool, isn't it? Way cool. And really beautiful to see.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5541175 - 11/26/12 10:18 PM

My inclination with regard to Io in perceiving it as a football probably varies with reason depending on aperture. I believe large aperture 12" or more might get an albedo config strong enough to suggest a flattend pole producing an oblate looking orb. Its plausible anyway. What I think is the greater reason is simply the vageries of atmospheric refraction. On Jupiter and individual details this serves to soften the image and erase finer lines and such but on the moons they are seen to move bodily, extending, flairing and so on and so this is perhaps the football. Howmany times have we seen a sharp jupiter image with a nearby galillean moon blurred or elongated? I would guess this elliptical or football appearance is that. I dont believe for a second though that tidal forces are squishing this very round object into an ellipse of torture. Its got its own hellish unrest due to Juptiers pull but it is forever as round as round can be for a moon anyway. If its out of round and ultimatley they all are its nothing wed actually ever see.

Id like to think this is a toe hold on Io discerning albedo in its own peculiar way or effect but Id be more in line with seeing vagueries and the manipulation these fine orbs are subject to through atmospheric lensing.

My .02!
Pete


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5541480 - 11/27/12 03:16 AM

Well, I get an Io transit tonight near around 11PM local. Jupiter is near the zenith, and if seeing holds...we'll take a gander.

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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5541581 - 11/27/12 07:14 AM

I look forward to the report.

Pete


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5541982 - 11/27/12 12:07 PM

The night was tense.

Okay, just observed Io and Jupiter for nearly 3 hours from 27/1330 to 1630UT. My scope was perfectly collimated. I know because in 9/10 seeing I tweaked the Poisson spot about half an arc second to dead center at about 1 wave de-focus. In focus was perfect.

If observing this elongation had a chance, it was tonight as Jupiter was approaching the zenith. Europa was on the other side of Jupiter, but Callisto was just 1' arc trailing Io. So, I had two good references for what round looks like. One in the same high power field of view.

Normally, I'd make you read the entire account, but I gotta say Jason might be onto something. I'll explain why below. But, this brings one question to mind. Why is this not common knowledge already? I mean, surely we're not doing ground breaking amateur observations, here. Surely someone has reported this before.

Okay, now the boring account. A bit before Io's shadow touched Jupiter's limb, I observed it at 320x (6mm TMBII.) I wanted to observe it against the black of space. At this magnification, nothing really struck me but I did get a curious feeling about it. Not curiosity, I already had that. But a, "hey, hmmm, that's curious moment."

So zipping up to 380x (8mm TMB II and 1.6x Barlow) there sat Io against a pretty dark background, for all intents and purposes. My first impression was, "Hey, that does kind of look like a tiny bright dash." But, always on guard for the mind's aperture effect, I noted it and kept observing. Over time, Io bounced and blurred slightly. It was sometimes circular, sometimes not. Inconclusive on the elongation, but that nagging feeling it might be hung in there. Glancing at Callisto, then back to Io several times gave the impression Io might not be exactly circular. But I wasn't sure.

Okay, well, let's see if atmosphere is causing this tiny elongated impression. Slewed over to observe Europa. In the same seeing conditions, it was pretty much a clean disc. It bounced and blurred a bit, but it never gave any hint of elongation. Okay, so Io gave some hint of elongation, Europa nor Callisto did. Now, I am becoming somewhat convinced Io might actually be, and just barely detectable as elongated. The same observations were made at "stupid" 520x (6mm TMB II and 1.6x barlow.) Same results, but bigger disc.

The shadow drug itself over the limb, and Io struggled to keep up. It made contact with Jupiter's limb. And you know what? The elongation effect seemed a touch more convincing. Still not enough to really call it with utter confidence of a WWF wrestler picking a match in a school playground. But, interesting never the less.

Okay, not convinced, but cannot deny it's not elongated. That was the verdict at this point. By the way, I managed to follow Io all the way across the planet. It was in the darker SEB southern edge just preceding the GRS. In fact, Io with it's shadow just ahead of it (a few arc seconds) was just preceding Oval BA and it's companion. The whole entourage (BA, Dark spot, GRS, Io and shadow) marched across the disc. I got a sketch of it. Sweet.

So, anyway, after the sketch was done and Io approached the preceding limb, it deserved another look. Back up to stupid 520x for another look. Now! This was the most convincing elongation. In fact, I'd almost bet my Christmas gifts it's elongated. It just looked like a tiny bright dash mark.

So, yea, I really think Jason and Eddgie are onto something. I think it certainly can be glimpsed as elliptical or kind of like a small bright dash. It was way to small for me to even say whether it was 3:2 or any other ratio. Just that it did not really look circular all the time.

In fact, 72 Pegasi was clearly elongated at 0.56" arc (380x), and Io was a tougher to see elongation. Just to give you some idea, some scale of how hard this observation really was.

That's my report. Your turn! (Forgive the lack of editing...tired.)


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5542026 - 11/27/12 12:30 PM

Interesting, and in step with what I think I may have seen. I genuinely enjoyed your report.

When I was observing it, at 200x, the seeing was such that the moon's disk was quite clean and round, though it would jump about by about half its diameter once in a while, presenting a reasonably clean and stable image for maybe 50-70% of the time. As good a night as I can hope for, here at sea level on the east coast.

I'm going to remain skeptical of my observation, but with some cautious optimism regarding it. It seems now we've got 2 folk who are seeing this curious effect, and that breeds hope! I'd love to hear some more accounts, successful or not. Skepticism is entirely warranted, I think, when we're attempting to observe some form of detail/albedo on a disk that is a little more than 2x our scope's resolving limit.

Last night held 50km winds for me, and Orion's bright stars were twinkling mightily when I looked out. With luck, the coming days may afford me another chance to observe this.

Thanks for your thoughts!

J


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5542058 - 11/27/12 12:48 PM

Well maybe your observations aren't groundbreaking Norme but I have it from first hand observation that the little spot between the GRS &BA is a monolith. So far my drawings show it to be of exacting dimensions. I should mention my scope spoke to me and said its name is Hal.

There.

Pete


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5542066 - 11/27/12 12:51 PM

Great! I was asking about the dark spot's name in a recent post... Well met, Hal the Spot!

J


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5542083 - 11/27/12 12:59 PM Attachment (29 downloads)

Jason, I plopped into bed of course still rehashing the observation. First correction, 0.5" arc was way more collimation needed to be prefect. Just a hair, just enough to brighten the NW section of the first ring a bit.

Then it dawned on me, is this even possible in a 6" with an Airy disc 1.84" arc? Io, according to JPL sim is only 1.2" arc. But, it is not a point source, it's an extended object. So, maybe more than a few tiny spurious discs overlapping at magnitude 5 might give it the edge into doable territory. I really don't know.

By no means was my observation conclusive, either. I was equally convinced Io was not circular as I was unconvinced it was elongated. Something like that. I was torn to whether it was or wasn't. The thing that struck me was, I was not torn about Europa in the same way. And not nearby Callisto either. It was that close, it was that difficult. Maybe the power of suggestion runs deep.

I dunno what to make of it. Like I mentioned, there was no doubt 72 Peg was elongated. Absolutely none. It's 0.5" arc. It was easy in comparison to detecting elongation in Io.

Surely it becomes easier in larger apertures, and I remain convinced it's doable, as you and Eddgie reported. I am convinced you might well have seen it. I mean, I am that close to believing I did, too. I just hope it's theoretically and practically even possible with 150mm aperture. If not, well, I must have experienced the power of suggestion. Surely that's always a possibility, especially when you are operating at the very absolute limits of our senses...pushing the envelop. You can bet I'll look again.

Thanks for pointing Io's effect out. I noticed it on images, but just thought it was an artifact of motion.

Edited by Asbytec (11/27/12 01:01 PM)


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5542090 - 11/27/12 01:03 PM

Okay, Hal...yea, that was funny.

"What are you doing, Pete?" Any more powers of suggestion you want to inflict in my head? Next time I sketch that spot (tomorrow), look for some very tiny corners on it. And maybe an ape nearby.

I might just add them for fun, though. A small monolith would be easy. I might can draw a monkey using about 8 pixels...

Edit: On a sad note, I /think/ I discovered a small cataract in my left (dominate) eye. I am of age to have them. Thankfully it's not directly on axis, but very occasionally, if I look at Jupiter at some specific angle it blurs pretty bad and has a small diffuse darkening imposed on it. My observing eye seems to be clear in this regard. And it seems a bit sharper and more sensitive. Gotta stick with it, I guess. Anyone else run across this?

Edited by Asbytec (11/27/12 01:26 PM)


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5542138 - 11/27/12 01:31 PM

I observe with my left eye that has less astig., but a floater nearly on-axis. A minor PITA and usually avoidable.

My right eye never turns in a good performance with optics, despite it being dominant, generally floater free and not much worse in astig than my left. No cataracts yet, thankfully, though my mother has developed'em.

J


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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 (23 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 (25 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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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5553806 - 12/04/12 11:35 AM

I should add to my post above that not only will white line look wider on a black background, but a short white line will appear longer on a black background because the ends will be extended due to diffraction. This is the critical element involved here. that the "Line" that is Io's brighter center region I think is being "Lengthened".

Anyone could see this effect using Abberator. Overlap two stars seperated by 1.2 arc seconds in a 6" apperture. Assuming the stars represent diffraction from the edges of a brighter central band, it should be easy to see that they are elongated.

And that was my point. Io is not evenly illumninated. Pictures show this and I can see it at the eyepeice. So, if it is illuminated unevenly, especially if it has a central band that is more illuminated than the limbs, you will be seeing diffraction effects extend out slightly further at the ends of the "Band" than at the top and bottom.

And the spreading does not start at the center of an Airy Disk that is represented by the center of Io, but by the edge of the disk. that is what the theory of image formation for an extended object says.. Every point on the object generates its own Airy pattern, so the spread of the Airy Pattern for points on either end of the brighter band will spread further than points from the edges that are darker (well, they will spread the same but be dimmer and it will be harder to see this spread).

Bottom line? Diffraction accounts perfectly for being able to see Io at 300x as slighly elongated if the disk is not perfectly illuminated.

In fact this is the exact result theory says you will get. So rather than be surprised, I would think that this would be the "Expected" result.

And Norme, this is kind of in tune with our previous conversation regarding "detecting" and "resolving".

You can infer that Io is not evenly illuminated because if it were, the disk would appear slightly larger than an Airy Disk and it would be perfectly round. It would have to be this way.

But if it appears elongated, you can infer that the disk is not evenly illuminated because diffraction clearly will cause the light at a dimmer limb to not be as bright as light from the darker limb. And of two limbs are dim, then you get a more distict elongation.

So, you have clearly detected that there is albedo shding, but have you "Resolved" it? In this case, if you could not tell which limb was actually dark (assuming that one limb was not fully illuminated for example) but the only evidence is that the diffraction pattern is not round, then you have clearly "detected' the presence of some detail.

But you haven't resolved it because you can't see where it is and how large it is relative to the disk itself.

And that is what I was trying to describe in our previous post. Sometimes I detect detail because of uneven illumination, but it is indistinct. I call this "detecting" that a detail is present. And you are doing this with Io.

But to resolve it, you would have to tell me what side it was on, and how much of the ark of the limb it occopies, and this would be just a bit blow the capability of the scope.

We can say though that the scope has sufficent resolving power to detect the presence though, the same way that it is done with double stars. Many people feel that a double is only resolved with a Daws split, but the Sparrow criterion clearly shows the presence of a double even though the star is not truely split. It is detected though, and that is why I think the term "Sparrow Criterion is used" rather than "Sparrow Split." It is a subtle difference. We detect it is a double because it is not round, but we can't actually spit the intensity curve, which seems more of a "Resolved" feature.

Anyway, perhaps now you can see why I prefer to use "detected" and "resoved." as different discriptions.


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5553809 - 12/04/12 11:38 AM

Yea, Eddgie, I am still chewing on what it means to resolve something that small. But, if I may...

Quote:

...both generate Airy Disks that are seperated by 1.2 Arc Seconds (the width of Io's Disk).

He can only "Infer" it because of the diffraction making the disk appear slightly elongated.




Exactly. Not easy by any stretch. In fact, I am wondering if a 4" could do it. That would be one for the books.

Quote:

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.




You know, resolution depends on contrast. And not just the length of several spurious discs in a row that end against a dark sky (devoid of any point source diffraction), but also the height of Io from pole to pole. I am not saying I saw any spurious discs from the poles, though, as you have.

In Raleigh, resolution means two white (half lines) and one dark. That is 1 line pair/one or cycle within the Raleigh limit. It could mean two dark (Io's poles) and one white (the equatorial region.) As long as those line pairs are resolvable at Raleigh (28% contrast?) or Dawes (5% contrast), then true resolution is said to occur. And those spatial frequencies are not even at the limit of the MTF, theoretically speaking. Dawes is not even at the maximum spacial frequency, but stops just short at 5% contrast. And that far out the curve, the spurious discs in an obstructed scope are smaller. Brighter on Io, but smaller, too. I think Suiter uses Abbe limit as maximum resolution. But those contrasts are, by convention, said to be between two bright lines (or technically point sources for double stars.) I am not sure I actually resolved the equatorial region in the pure sense. Interesting thinking about it, though.

Io is different in that resolution is exactly like the one white line between two darks you describe. So, even at 1.2" arc, that frequency is still well (outside) the Raleigh limit (half the Airy disc, a dark space, then half the other Airy disc with the centers separated by 0.92" arc. Right?)

You might be able to go even smaller to the Dawes limit which is an even tighter line pair. But at 5% contrast at the poles, one might imagine it get's a lot more difficult at this point and beyond.

Then there is the complicated math governing multiple point sources with decreasing optical path distance. At zero OPD, the Airy disc actually expands both in diameter and in intensity. At greater OPD, such as Io's multiple Airy patterns, the Airy (an spurious) discs returns to pretty much normal in both aspects.

I still don't fully understand how to apply the latter.

Quote:

..In fact it stands in stark testimony to the laws of physics, resolution..




I think were we might talk past each other is in the way resolution is "defined." Resolution, per se, is not a law in that it can only occur the way Raleigh, Dawes, or Mr. Sparrow say. They define resolution as some level of contrast between two points and then develop their math from that definition. But, I guess the Airy disc is a law of physics, Dawes really is not. But, it helps if we all use the same definition.

-----------------Off topic------------------but related.

I was skeptical of Uranus observations, well, because 2% (low) contrast on the planet is just not modulated through the scope efficiently enough at that spacial frequency. It would be visible on the focal plane, where a CCD could capture it. But the human eye just could not resolve such low contrasts. Not average vision, anyway. The other thing that bugged me was the color of the bands so far into the red.

But, hey, that's theory. Today I take it a bit easier on those claims and offer the benefit of the doubt. He might just be able to do it, and a few others with exceptional abilities as well. But, again, that's the skeptic mind set, to shrug it off as impossible when some document somewhere proves it can't be done. Well, here we are...

I no longer totally doubt the Uranus observations. Still have to overcome some skepticism, though. But, an open (and suggestible mind) helps immensely.

Edited by Asbytec (12/04/12 11:55 AM)


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sqrlman
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5553819 - 12/04/12 11:41 AM

I was not commenting on Io while in transit. I was commenting on the observation of Io looking like a boxcar floating in space. I have spent enough time at the eyepiece to know better than that.

Steve


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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5553859 - 12/04/12 12:07 PM

I've never observed Io to appear non-circular when not in transit. To me, it (and the other Galilean moons) have always appeared to be purely circular against the blackness of space.

J


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5553881 - 12/04/12 12:26 PM

Well, it is a semantic difference to be sure.

You might see a bright spot at the edge of he limb of Ganymede and look at a simulation and say "that is Osiris" and be right.

I would look at Osiris in my scope and see that it is not on the limb, but in fact a measurable distance inside the limb and have given it a size, shape, and position.

We both see Osiris, and we are only debating my own defintion of "resolved" (shape, size, and position) with yours (see something that is in generally in the right place at the right time, so must be Osiris).

Again, we are debating the samantics of it, but I for my own records, I tend to differentiate this. The fact that I could seee the size and position of Osiris in the C14 and could never see it in any of my other scopes made me redefine these terms for my own use so when I look back at my logs, I can see that "Resolving Osiris" for me personally had a much more secific meaning than having seen it as an albedo feature (a slightly brightend area on the limb with no distint shape to indicate it was a seperate feature) in my 6" scope.

So, perhaps we are just debating the "Relative" nature of our resolution of these objects. And to me, they are far more "realatively" resolved at 14" than a 6".

And this is why I am so adament that the best planetary result is going to be had with aperture. It is the single most important attribute of a good planetary scope. The bigger the aperture, the "Better" the resolution.

And for me, the meaning of resolution evolved as I started seeing more granularity in the shapes and positions of details on the surface of planets and moons.

So, no point in arguing it because it is semantics, but i don't at all doubt that in a small scope, Io could appear less than perfectly round due to albedo shading and diffraction. It is all to easy to explain it using this mechanism.

If disk does not appear as perfectly round, it can only be because there is a difference in brightness present on the surface, and this would exactly explain it.

Supose that Io were seen in a Half-moon type lighting. One edge would be "Flat" and the other "Round"

If the half of the disk that was illuminated was 1.2 arc seconds in diameter, the light from the edge of that disk would form a perfectly straight line that was 1.2 arc seconds long and displaced the width of the radius of the Airy Disk.

If you magnified this image 300 times, you would see a circle of light that was flat on one side extrending 6 arc seconds in the eyepiece on one side of what would appear to be a very slightly flattened circle of light.

This is 100% consistent with how extened objects are formed. It would be easy to see if conditions were perfect because the amount of flattening would be significent enough that the other side would bulge away with sufficient curvature to be seen. It would actaually be much larger than the half disk that formed it, but again, this is what diffraction does. It takes the energy from the point that originated it and spreads it out past the point.

You are working at the extreme edge of visible perception, but honestly, I personally think that your observation is not only possible, but probable if the limb darkeinging is extreme enough.

I mean after all, Sparrow did it with a Double Star! (though he measured it using a camera, but that was clearly a case where he detected the presence of a doube star simply because the Airy Pattern he observed was not round anymore).


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5553893 - 12/04/12 12:34 PM

And here is another picture that shows the extreme contrast variation in Io.

I could easily see this in the C14 during a recent transit and reported it on this forum. I reported that Io looked like a rivet standing out against the planet and attributed it to albedo dimming at the north and south when the planet was in the sky.

And agian, I said it made the moon look like a pearl.

And someone else posted and said that they thought I was over-stating the situation until they observed it in their 8" scope..


Hmmm. Is it impossible to believe that it could not be detected at 6"?

Clearly there is no magic cut-off where this just suddenly stops. It gets progressivly harder and harder to see as the aperture gets smaller and smaller.

At 14" it was easy. At 8" it was easy enough that someone that looked for it saw it and reported it here.

Why should we be surprised that someone using a 6" scope noted the effect when two other people have reported it, and we have a picture that shows it clearly, and diffraction can easily explain why it looked elongated.

Great picture. Clear to see that there is strong contrast drop-off at the north and south. Saw it in my C14.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5553738/page...

Anyone that cares to can step back and tell me if it doesn't appear to be like a little dash... In fact the further you step back from the monitor, the more obvious it becomes.... Hmmmm. From four feet, it does kind of look like a little box car..

Edited by Eddgie (12/04/12 12:37 PM)


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5554179 - 12/04/12 03:31 PM

Above post, I think I said five arc seconds, and of course that is silly. It would make a soft, straight line 5 arc minutes long at 300x. Easy to see a 5 arc minute long detail as a line.

But again, this was just an example of how the image could form if the top and bottom of the moon were darker than the center. You would essenitally have two gently curved lines 5 arc minutes in length that would look, well, like a football.


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5554474 - 12/04/12 07:14 PM

I have observed a number of transits during this Jupiter season. My eyes start playing tricks on me after staring through the telescope for a while. I was watching a bright/shadow transit of Europa and I swear I saw a momentary flash of bright light in the transiting shadow of Europa. Was it really there? Impossible to say, but I definitely perceived it and enjoyed it greatly. You may never know if what you perceived was real, even if others confirm that such a phenomenon is possible to observe. Remember the canals of Mars? I'm sure Giovanni Schiaparelli enjoyed seeing them, no matter the ultimate outcome of the observation.

/Ira

Edited by Ira (12/04/12 07:17 PM)


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Re: Some thoughts on a Transit of Io new [Re: sqrlman]
      #5554493 - 12/04/12 07:25 PM

Quote:

I have spent enough time at the eyepiece to know better than that.

Steve




So, we should take that at face value because you say so? Why should we believe you? I'm skeptical of your're claim, or could be if I were serious (but am not.)

Not trying to be contentious, just driving home a point. You made a claim that is not substantiated in any way, not even in theory nor with any data to prove otherwise. I have no reason to doubt you have plenty of eyepiece time, so I accept what you say at face value.

The point is, there is something strange with Io and I wish you could see it, too. And don't think for a moment those doubts don't come creeping back after a day or so. They do.

Edited by Asbytec (12/04/12 08:56 PM)


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5554667 - 12/04/12 09:25 PM

Quote:

So, perhaps we are just debating the "Relative" nature of our resolution of these objects. And to me, they are far more "relatively" resolved at 14" than a 6".




No doubt. You know, there was a thread Pete did asking about resolution, I'd hate to repeat it here...but the urge is overwhelming. Raleigh and Dawes both offer resolution in terms of a contrast between two point sources. This is the standard by which they say two stars can be seen distinctly as such and separate from one another.

However, if you think about it, they are not differentiating contrast from one star to the other as both have equal brightness hence no distinct contrast from one another. The real contrast is from the bright point and the black of space. In their case, they say that blackness must exist between the centers. But, that blackness contrasts with the brightness on all sides. So, really, if one star's bright pattern protrudes into the blackness of space, it can be said to resolve if we stretch the semantics a bit.

In other words, there is enough contrast around the star to see it. And because we know diffraction patterns are circular (cheating a bit) an elongated star must be comprised of at least two diffracted points. In a sense, this realization is resolution by contrast, too, just not between the centers. If the star is so dim, say less than 5% brighter than the blackness of space, we'd never see nor resolve it no matter the separation.

But, yes, in the classic sense, nothing was resolved on Io, best I can tell, in a 6". Certainly a C14 culd do a much better job on Io and Ganymede. On Ganymede, as you say correctly, nothing was distinctly seen like a well defined, large lunar crater. But, the brighter "spot" indeed represented one half of a line pair with a low contrast darker (opposite) limb comprising the other. And all of that within a space larger than the Raleigh limit.

Anyway, we're having that discussion, again, ain't we.

But, I agree with you. If Io had a brighter equator, and it does, and it was a certain angular dimension dependent on aperture and Raleigh's laws, then the spurious discs produced should appear elongated. And if they are darker at the poles, it would not appear circular nor resolved in the classic sense. We both understand that pretty clearly.

I also agree with you that it's not only probable, but it is the likely outcome. That's part of what makes this an exciting thing, it should be possible and yet such an observation is not common knowledge. Maybe it should be. And it's certainly not an easy one, either. It requires sub arc second seeing, even just a fleeting moment of it would suffice given, as you say, the right stuff (perseverance.)

I applaud Jason for bringing this up. I applaud you for having made the observation more convincingly and reporting it in the face of those who will argue otherwise. I applaud Pete for busting through those theoretical barriers (kind of described above) making the realization such things are, indeed, possible despite the Dawes limit. I applaud anyone willing to see for themselves and report back. And I applaud myself for being excited about all this.


What a fascinating topic, Jason. This just added another dimension to this year's opposition, like no other. Gotta run, my pills have arrived.

Edited by Asbytec (12/04/12 09:26 PM)


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Re: Some thoughts on a Transit of Io new [Re: Ira]
      #5554829 - 12/04/12 11:12 PM

Ira, certainly good points. They eye and the brain can do amazing things, whether we like it or not. Perception is reality, I guess. But is it? I can see my cell phone sitting right in front of me, so I am pretty sure it's there.

Yea, can't argue the canal mystery. Some thoughts, though. It was definitely shown canals do not exist on Mars. Not that anyone doubted they were perceived, but they do not exist. Images of Io, however, clearly show the phenomenon exists. That may not be conclusive in the strictest sense, but it is supportive of the observation. This is support the Canal mystery did not have, outside of a few Martian features that might have been seen as canals.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Ira]
      #5554895 - 12/05/12 12:12 AM

Quote:

I have observed a number of transits during this Jupiter season. My eyes start playing tricks on me after staring through the telescope for a while. I was watching a bright/shadow transit of Europa and I swear I saw a momentary flash of bright light in the transiting shadow of Europa. Was it really there? Impossible to say, but I definitely perceived it and enjoyed it greatly. You may never know if what you perceived was real, even if others confirm that such a phenomenon is possible to observe. Remember the canals of Mars? I'm sure Giovanni Schiaparelli enjoyed seeing them, no matter the ultimate outcome of the observation.

/Ira




To that end why observe at all?

Fact is his visual o servations are supported by electronic imaging. Too he's got a record of success and failure meaning if something's not showing he's not dreaming it into being. Frankly at this point it'd be irresponsible to ignore his observations.

I know where your going with your argument but there is compelling testimony this is real.


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5554992 - 12/05/12 01:58 AM

Pete, I still owe you Titan's disc, right? You say it's possible, theory says it's possible. But, I'll be darned if I have seen anything but a point of light with a faint ring. Maybe it's just so small an image. Gotta keep at it. It's fun trying.

I know I saw Enceladus once. It took a few hours on good nights over a week to actually do it again.

Do I owe you Alpine ridge, as well? I forget. You drive us to observe the seemingly impossible. Quite often you are right, in fact surprisingly often. Your infatuation with blowing past stated resolution limits is well founded, IMO. The results are staggering.

Observing is an adventure, not a quick weekend warrior look-see at Jove that reveals little.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5555076 - 12/05/12 04:08 AM

Pete, thinking of Titan and trying to stay related to the topic of difficult observations.

You know, Titan is about 8th magnitude and right at ~.9" arc. That's exactly the size of a 6" Airy disc, if that matters. Being that dim, it appears smaller with a brighter center. Not only that, each point on Titan is a little dimmer than it's stated magnitude. So, really we we have is a series of, oh, 9th magnitude(?) point sources at best. Of course dimmer along the limb.

So, we have, say a 9th magnitude point source at the center and dimmer ones toward the limb. But the bright central spurious disc will not completely overlap the others. Not like it would if Titan were a 6th magnitude star nearly 0.9" arc across. So, the limb sources should poke out. Question is, how much and how bright.

So, to see Titan's disc, I have to see something that IS the size of the Airy disc (which is larger than the point-like spurious disc I do see) and much fainter than Titan itself. If I can get below limited magnitude of about 11 or 12 (about the limit so far this year), then it might be doable. Those dim limb point sources have to stand out against the sky with at least 5% contrast. So far, seems only the central spurious disc, or two, does so.

You know, given dark enough sky, good transparency, dark adaption, and some steady seeing those limb point sources might just stand out a little better than previous experience. And each should be a bit brighter than Enceladus (~12 mag), I think. It should not be as difficult as Enceladus (hours of observing it's location waiting for that brief speck to pop once, maybe twice.) So, I wonder why I have not been able to resolve a disc, yet.

Maybe I am overestimating its surface brightness. If memory serves, it does appear like a faint, fuzzy spot - nothing like Europa, for example. So, no clearly defined disc. It really does look like a faint star. But, there is enough energy from that spot to produce a faint ring, further reinforcing it's star-like appearance.

Gaaa! I cannot decide if it's doable or not. Sounds like it should be. I mean, come on, we should be able to see discs of the solar system's largest moons. How hard can that be?

Maybe this deserves it's own thread when the time comes.

Edited by Asbytec (12/05/12 04:09 AM)


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5555211 - 12/05/12 07:22 AM

This past summer I gave Saturn a gander on a night with 5-6 seeing and looking at TItan at 200x I was kinda put back a bit. It IS definstrly fainter in the 6" sct. It took 364x with the 8" juusttt to eek out an orb. I couldn't see it being any easier for a sct of that size then given how it was at 200x. I don't know about this one. Its the dimness that's really ramping up the difficulty.

Thanks for the kind words about challenging objects but its actually been my wish and your reality at times like the Catspaw!!! Ill see it sooner or later but probably with a setting sun angle as you have as its easier for me to observe later than earlier.

OK off to work.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5555298 - 12/05/12 08:52 AM

I think the issue that often rears its head in astronomy is the term resolution being used as an absolute value for true recognition of a feature or albedo shading. The problem is it becomes a very relative term with each each increase in aperture revealing how little truly was resolved prior. A 1 meter scope on pic d midi could leave the C14. Views interpreted as detected but not resolved. There's nothing absolute about the term resolved that is anything but a relative term. Detection is merely the beginning of resolution but its still resolved... just on the most basic level. I understand the diffraction line effect here but it is an effect born out of the reality of the physical state of its albedo or reflectivety. Something not born out of a true physical state or shape are diffraction rings. Strictly diffraction generated. In the case of Io the line is a simplified representation of reality. Yes there's effect there but its a close link to the actual albedo patterning.



Pete

Edited by azure1961p (12/05/12 08:54 AM)


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5555351 - 12/05/12 09:36 AM

I really want to revisit Io in the coming days, soon as the late season typhoon passes.

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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5555649 - 12/05/12 01:04 PM

Typhoon.... wow and I get bumped if its partly cloudy

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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5556213 - 12/05/12 07:03 PM

My thoughts are one of excitement now Great looking skies (in a relative kinda way). Much like waiting for a good concert or good movie to start

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Re: Some thoughts on a Transit of Io new [Re: wky46]
      #5556978 - 12/06/12 07:28 AM

LOL, I've seen some blue skies in the past couple weeks, but precious few starry nights.

I was poking around into the early visual explorations of Io yesterday. I ran across several descriptions of the earliest observations of surface detail on Io. The following passage, pilfered from Wikipedia, struck me, especially the conditions under which Io's albedo variations poles vs equatorial region were first noted - While in transit.

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

"Beginning in the 1890s, larger telescopes allowed astronomers to directly observe large scale features on the surfaces of the Galilean satellites including Io. In 1892, William Pickering measured Io's shape using a micrometer, and similar to his measurement of Ganymede, found it to have an elliptical outline aligned with the direction of its orbital motion.[23] Other astronomers between 1850 and 1895 noted Io's elliptical shape.[21] Edward Barnard observed Io while it transited across the face of Jupiter, finding the poles of Io to be dark compared to a brighter equatorial band.[24] Initially, Barnard concluded that Io was in fact a binary of two dark bodies, but observations of additional transits against Jovian cloud bands of different brightness and the round shape of Io's shadow on the Jovian cloud tops caused him to change his interpretation.[25] The egg-shape of Io reported by Pickering was the result of measuring only the bright equatorial band of Io, and mistaking the dark poles for background space.[21] Later telescopic observations confirmed Io's distinct reddish-brown polar regions and yellow-white equatorial band."

I believe EE Barnard's observations were made on the 36" Lick Refractor.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5556988 - 12/06/12 07:39 AM

Jason thanks for the remarkable historical account. I had no idea this was as documented as it is.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5557025 - 12/06/12 08:08 AM

Yea, fascinating! Lemme read the whole thing. Thank you, Jason. Wonder if there any other accounts out there.

The reference for Bernard cited, "[24] Barnard, E. E. (1891). "Observations of the Planet Jupiter and his Satellites during 1890 with the 12-inch Equatorial of the Lick Observatory". Monthly Notices of the Royal Astronomical Society 51 (9): 543–556. Bibcode 1891MNRAS..51..543B."

And one from Sky and Telescope, "[23] Dobbins, T.; and Sheehan, W. (2004). "The Story of Jupiter's Egg Moons". Sky & Telescope 107 (1): 114–120."

It's good to know we're not completely bonkers.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5557079 - 12/06/12 08:49 AM

Oooh, shoulda read that reference, LOL. I saw Lick (elsewhere) and thought 36", natch. What Barnard could discover with a 12", surely we can observe in less.

Found a PDF of the S&T article... Haven't read it yet!

http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid=c1e49d6a-e0e7-49d0-a7f...

J

Edited by JasonBurry (12/06/12 08:51 AM)


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5557096 - 12/06/12 08:59 AM

Grabbin some coffee...


Edit:...

My scope does not have enough astig to cause Io to elongate even that much and Europa not to at all. Star testing looks fine, too. Sometimes I see a tiny bit when seeing deteriorates, but that doesn't count.

Pickering claimed the elongation could readily be seen in 4 and 5" scopes under good conditions! Of course, I agree with Pickering, crazy as he was. God bless him.

Larger scopes clearly show Io as circular, as we know. But also explain Io, in particular, as giving an elliptical appearance due to it's EQ band, just as Eddgie discussed at length. Yea, it's circular, but it doesn't look that way. And that get's back into the resolution debate...

The same stuff we say today are reasons to doubt the observation: seeing, cooling, and collimation. I will tell you, all of those variables were minimal and non existent, respectively, during my observation.

Pickering saw what he saw and concluded Io was indeed elliptical when it is not. That's probably bad science, but you gotta appreciate his attempt to explain it. All I am saying is, I know Io is circular, but it does appear elliptical, visually...just as Pickering said.

Wow, fascinating read...full of observation, skepticism, and intrigue. Yes, Pickering was wrong, Io is spherical. But he was also right, IMO.

Quote:

That was some interesting reading... Barnard's sketch in the article is illuminating, too.



Oh, heck yea it was!

Edited by Asbytec (12/06/12 10:01 AM)


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5557133 - 12/06/12 09:30 AM

That was some interesting reading... Barnard's sketch in the article is illuminating, too.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5557281 - 12/06/12 10:57 AM

Jason, thank you so very much for introducing these historical accounts.

I had 100% confidence in Norme's observation and still feel confident that my diffraction explination explains why he was able to detect this even using a telescope that others thought would be sub-Airy Disk in size.

I have been trying to explain Contrast Transfer (MTF) in these forums for a couple of years, but just gave up, because people did not seem interested, or didn't belive in it, but it totally explains why Norme could see what he saw. In fact, it "Demands" the result he got. He could not have seen it any other way.

Anyway, I really appreciate your finding this and posting it.

I often get the feeling that there is some skepticisim on the forums, and often I read accounts that based on my own experience I am inclined to accept while some people perhaps attribute it to "You see what you want to see."

But I see what I see and I only consider it as truely seen when I have seen it at least three times in the sesssion distincly, and for planets, I have validated it using a simulator to show if the feature I observed was present on the disk at the time I made the observation.

I think the guys on this forum that did these observations need to be recognized as having the patience and persistance required to be satisfid that their observations are concrete. These clearly were.

And as we can see, some remarkable observations can be made with a smallish aperture, but once again, the more aperture, the better the resolution that can be achieved, and this thread is a perfect example. Norme saw it as a slightly elongated diffraction pattern, the 8" observer got a similar imression but concurred with the "Pearl" analogy that I use, and in the 14" scope, it was very clearly round, but with albedo darkening at the north and south.

Three scopes, three observers, three slightly different but totally explainable degrees of resolution.

And once again, history repeats itself..

What a great thread!

Edited by Eddgie (12/06/12 11:04 AM)


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5557367 - 12/06/12 11:47 AM

Quote:

And once again, history repeats itself..

What a great thread!




I agree totally, so stoked over this thread. One for the books, for sure.

What's amazing, Eddgie, is you, Jason and I are walking in the footsteps of the giants, the pioneers of planetary observering. We rediscovering, recreating history without even knowing it, and the same uncertainty, skepticism, and what have you that labeled Pickering a crack. "It's tube currents." LOL

Of course Pickering was wrong about Io's shape, but he was correct that it appeared that way. That's the point. Thanks to this thread, we can scratch one more of Jupiter's moons off the list of featureless discs. I think that's a small step for man, one giant leap for amateur observing.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5557421 - 12/06/12 12:17 PM

I think Pickering WAS a crank.

He illustrates beautifully the hazard of being too sure of one's own assumptions, of the mind's ability to make the observation match the expectation, and the second hazard of making oneself so convinced of one's own interpretation, that he remained convinced of his own correctness, despite a mountain of evidence to the contrary.

To me, Barnard is the real hero of the story. He observed, interpreted, re-observed, and re-interpreted. From "binary" to a bright sphere with darker poles, as he integrated the information of subsequent observations.

It is the likes of Barnard we should aspire to. Observe and report, evaluate, keeping the mind open to the possibilities, rather than clinging to our first notion.

But the descriptions of these historical observations of Io are strikingly similar to the early posts in this thread. Clearly, we were unintentionally reproducing these historical observations ourselves.

Io is indeed more than a featureless disk, even to a visual amateur with modest equipment.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5557497 - 12/06/12 12:55 PM

No argument from me, Bernard and company moved our knowledge of Io forward. But, it's really enjoyable relating to the history.

Not that it means anything, but I have a soft spot for the cranks and rebellious sorts, as long as they are pushing the boundaries and are sensible in the end. Even if they fail, sometimes those are the pioneers, too, even if they simply draw attention to the idea. Regardless, they are often part of a larger story. History. Even Pickering has a place.

As I said, yea, he was wrong in the end, but it feels good to see Io as he did. To suffer a little wrath of skepticism (even with some re-emerging doubt of my own. Really want to look again to be sure.) But, it really plays to my soft spot for the cranks in life.

It's interesting this is a phenomenon that has been brought up before and debated. And rediscovered. I think that persistent aspect adds credibility to the tale. (Well, it adds cred to big foot, too, I guess. )

And we all know better these days, we have a mountain of evidence. Your point is well taken. No one can easily convince me Io is elliptical (or that big foot exists.) Io just /looks/ that way. It is an illusion of sorts in smaller apertures. It only appears strange because of the nature of light.

I'm pretty much convinced it wasn't tube currents or astigmatism and it's a real phenomenon. And that others should see for themselves. That's my whole motivation. If that happens, Io will become common knowledge and could be as popular as E and F Trapezium.

But, if someone tries to convince me Europa is elliptical as Pickering said, I am gonna need a bigger scope.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5557554 - 12/06/12 01:28 PM

Oh, I can assure you that the result was a consequence of diffraction.

I have made many many attempts in these forums to explain how diffraction and MTF are related but most people are either not interested, or are skeptical.

One of the reasons that this topic is important is 100% relevant to this thread.

Much is made about the contrast advantage of refractors vs obstructed instruments, every MTF chart I have ever posted has shown that at the limt of the resolution of the aperture, the obstruted scope actually has an Advantage!

And the tube currents theory is hogwash.

The theory of diffration and the study of MTF would immediatly show anyone that bothered to study the topic that in your telescope, Io had to appear the way it did. Diffraction and contrast transfer demand this outcome!

And our three stories are glaring confirmation of one of my primary messages over the years.. The best way to see more detail on planets is to use more and more aperture, and exercise the patience needed to allow that aperture to work to its potential.

Our three experiences show this. In Norme's scope, diffraction forced the central region to bleed off on the dark northern and southern hemispheres and obsecured them, and lengthed the central band. It had to be that way.. That is what diffractiion does.

In the 8" scope, the energy from the central band was more concentrated and closer to the edges of the bank, but still intruded into the polar shaded area. The 8" scope observer starts to see that there is a hint of sphere, but it is only a hint.

The 14" aperture observer has light from the edge of the bright band that falls mostly into the hemisphere and does not bleed over the edge, allowing the less bright limb of the hemisphere to still show, so the 14" aperture user sees a very distinct edge.

How this could not be obvious to anyone that has studied diffraction and contrast transfer would escape me, and to suggest that tube currents were responsible to me totally dismisses the effects of diffraction on extended targets.

These forums will continue to have these debates becasue it appears to me that most participents really don't want to invest the time and energy to become educated to the specifics of MTF and image formation in an extended object.

So we are doomed to suffer countless incorrect statements that refractors are better than reflectors, and that smaller apertures are better for planets, and that this or that observation is not possible.

But in the space of this one thread, all of these things need to be taken as gospel. More aperture almost always improves the chances of make a given obeservation, and contrast transfer only lowers contrast in a part of the range of the instrument, but an obstruction by itself does not prevent anyone from seeing this kind of detail, and in this particular case, may have actually enhanced it (and that is what that elbow and rise in the MTF charts I always post clearly show... An obstructed instrument can outperform an unobstructed instrument when used at near the limit of their capabilities!!!)

This thread should be a sticky. It clearly embodies all hat is good in planetary observing for dedicated amateurs, and it clearly presents the absolute advantage that apeture brings to bear on high resolutoin planetary observing.

My bet is that the clash of tiny swords that so typically dominates these forum will not be affected by it though.

And that is a real loss for the community. No one wants to raise the game.


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5557596 - 12/06/12 01:58 PM

And forgive me if this is turning into a rant, but the first thing you learn when you study contast transfer is that diffraction has this specific effect.

A white line on a black background will appear wider than it is, and the smaller the apeture, the wider it will appear against its the black background (and longer if its lenght is limited to less than the area observed).

A black line on a white background will appear narrower (and shorter) than it really is and the smaller the aprture, the narrower that black line line will appear. (and longer if it is complelty contained within the focal plane).

This is the most fundamental aspect of contrast transfer. It is one of the first things that anyone writing about the subject will say because it is the basis of all contrast transfer theory.

The same thing of course happens if the line is not black or white, but various shades, representing different contrasts. The lighter colored line will bleed to the darker background and the dark line will appear thinner because the ligher area on either side bleeds over (and this is what the first and subsequent rings do).

And here we have exactly this situation. This is textbook diffraction lowering the contrast of the limbs to the point that they are obscured in the small aperture.

And while this forum routinely suggest that details smaller than the Airy Disk cannot be detected, MTF threory does not agree with this, and in fact double stars have been routinly detected simply because of the elongation of their overlapping Airy Disks, when no perceptible dip in brightness between theh cores has been observerd.

One has only to substitute the brighter band at the center of Io and the darker north and south hemisphere as a white line running between two dark lines!

And that is What Norme saw. In essence, the light from either limb was acting as two stars seperated by 1.2 arc seconds in diameter.

But because the light intensity is spreading out from the center (where the edge would be) in all directions, more than 50% of that light is going outside of the border of the limb of the moon, and this is happening on each end of the moon, so it is making the moon appear about 1.2 arc seconds longer in one dimension than the other!

And at 300x, this looks like an Airy Disk that has been stretched! It is so blindingly obvious that this is a result of diffraction that it amazes me that anyone would even question it.

But as I said, I don't believe that the theory of MTF and resolution for extended targets are very well understood on these forums, so people will still doubt me.

I am used to it, but one has to ask themselves how it so perfectly describes what each of the three observers involved witnessed.

This is Textbook MTF and Linear Resolving power stuff. Exactly as threory predicts. How does that happen? Just luck?


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5558424 - 12/06/12 10:54 PM

Geepers Eddgie, I've always appreciated your input.

Pete


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5558427 - 12/06/12 10:56 PM

Eddgie, yea, some of the arguments might confuse aesthetics with performance. Surely more than a few have learned much from your MTF discussions. I have.

I need to re-read the article, but it does seem Pickering was viewing through a 13" refractor while Bernard observed through a 36". That is plenty of aperture difference to turn elongation perceived by Pickering into a sphere with a bright equator. I suspect Pickering's fault was not in measuring elongation, but in explaining it, as Jason said, despite the preponderance of evidence. One has to wonder what Bernard saw in his 12" reflector. Maybe elongation, maybe nothing. But, he eventually took it to a new level with the larger aperture.

And you are correct, diffraction dictates what we DO see. Each of us has seen what we should have seen, from simple elongation to actual resolution of the poles. Detecting a very tiny bit of elongation is very difficult - enough to warrant caution before concluding it was so. But theory and the early observations support the phenomenon can actually be seen.

I am convinced Pickering did not suffer from astigmatism or tube currents, but maybe he was under a spell of illusion based on what he DID see. And that is what we can see, too, but we are not under any illusion about Io's actual shape. Today, we know better. But that makes the actual observation no less exciting. And convincing, IMO.


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5558741 - 12/07/12 07:12 AM

Quote:

Geepers Eddgie, I've always appreciated your input.

Pete




+1

I took the time last night to re-read this entire thread, including the discussion of contrast, diffraction and resolution. I've come away from this observation and its discussion with much new knowledge, and a cool smattering of history to boot.

J


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5558760 - 12/07/12 07:38 AM Attachment (15 downloads)

Eddgie, maybe this will help your explanations. I'm a CAD operator in real life, and I used CAD to do a rough simulation of the diffraction effects involved in our observations of Io. I humbly submit it here for discussion. This models an 8" telescope with no CO, giving an Airy disc of 0.68". I've laid multiple airy discs over a grid laid on the face of "Io", with equatorial region discs shown bright, and polar discs shown darker.

It's a good likeness to what I observed, allowing for my crude simulation.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5558763 - 12/07/12 07:42 AM

Beautifully done.

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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5558769 - 12/07/12 07:51 AM

It worked out rather better than I'd hoped...

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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5558847 - 12/07/12 08:51 AM

There may be a brief pause in the action, but this is an amazing thread. It's an amazing topic. More folks should be repeating the observation.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5558905 - 12/07/12 09:34 AM

Indeed. I'm still chasing down some of Barnard's historical accounts of this observation.

From the Wikipedia article "Exploration of Io", I followed the reference to this link:

Barnard's observations of Jupiter and its satellites

I ran that document thru OCR, so I could paste some relevant sections here. They are presented below:

Page 5:
****************************************************
In connection with the black transits of III. and IV. I have often seen I. transiting as a dark or dusKy spot. On Sept. 8, .189°, with the I2-inch this satellite presented a remarkable aspect while in dark transit. I noticed that it appeared elongated in a direction nearly perpendicular to the belts of Jupiter.

With high powers (500 and 7°°) and perfect definition the satellite appeared distinctly double, the components clearly 'separated. At my request Mr. Burnham kindly examined the satellite with me, and we both distinctly saw the phenomenon of apparent duplicity (see Ast. Nach. 2995). In reference to the appearance of the satellite-whatever may be the explanation-Mr.
Burnham has no hesitation in stating that it was as distinctly double as any double star that he has seen. The distance
between the centres of the two' images was about I", and the position angle at transit 173°+. The south component was very
slightly the smaller (Plate 14, fig. 4). It was not possible to follow the satellite closely, because of interruption by a number f visitors, and the great telescope was not available for observing the phenomenon.

I have offered two explanation'S of this phenomenon (A.N. 2995)

1st. That the satellite had a white belt on it parallel to those of Jupiter, or

2nd. That the satellite is actually double. I do ,not now think that the first of these theories is satisfactory, as it would
require a far whiter belt than we have reason to believe will exist on the satellite, reasoning from our knowledge of the
phenomena of Jupiter itself. I am strongly inclined to favour the theory of actual duplicity.

It may be asked, If the satellite is double why has it not so been seen when projected on the sky, if the distance is as much
as one second P In the case of two stars this distance would be very easy with any considerable telescope. We must ·remember,
however, that in the case of a donble satellite we should have two sensible discs, which would perhaps never be well enough
detined to show a maximum separation of only one second, while the greater part of the time the distance would be much less than this. H, however, the satellite were projected on a background brighter than itself it would appear reduced to its minimum size, so that if 'duplicity existed the chances for detecting it would be far more favourable. To better illustrate my meaning Mercury is a very brilliant object to the naked eye about the times of its greatest elongation. Yet when this planet crosses the Sun it is shorn of its light and cannot be seen with the unaided eye, though it is then a fifth nearer to us. On this same principle if the satellite consists of two moons the largeness of their ill-defined discs would make them appear as one in a telescope. Transferred, however, to a bright surface, the confusing light is got rid of and the size of the object is reduced to a minimum, and if double then will be the most favourable time to detect it. If this satellite is really double, the components at the time of my observation were probably at tbeir greatest elongation. If so this would indicate a distance from centre to centre of some 2,000 miles. The individual components would be about 1,000 miles in diameter, and their orbits nearly perpendicular to that of Jupiter, with a period of revolution of a few hours. I trust that this satellite at its transits this year will receive the closest attention with powerful telescopes. It should be examined with the highest powers, and the direction of elongation, if any, carefully noted. If double, I have not much hope of the components ever being seen when projected on the sky.
****************************************************

Barnard goes on on the last page of the document, discussing the possible double nature of Io. We, of course, now know that he has chosen the wrong answer among the 2 posssibilities he had noted, and he would in the future revisit this, and come to the correct conclusion, that Io is 2 dark poles sandwiching a lighter equatorial region.

And he DID make these observations with a 12" refractor, following up later with the 36".

J


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5558940 - 12/07/12 09:57 AM

Brilliant. Beautiful peice of work.

Yes, this shows far more clearly what I could not say in 1000 words.

Applause. Heck, standing ovation!

This picture shows exactly what MTF is about. An extended image is (in theory) composed of an infinite number of overlapping Airy Disks, and the brigher disks will overlap the darker disks, raising the brightness of what would be a dark feature, so that feature becomes less visible.

And the larger the scope, the less overlap there is from the diffraction rings, so that with more aperture, more of the limb (in this case) is preserved.

What a wonderuful depictation.

And as I said earlier, this to me is what a viewer in a small scope would have to see. Diffraction and MTF almost demand that Io would appear this way in a smaller scope.

And I don't think tube currents were the issue for those observers so long ago.

Most likely their diffraction effects were much worse than with telescopes made today (a lower Strehl ratio back then, I am positive) so even the larger scopes may have been producing somewhat poor contrast and contrast is after all a function of contentrating as much energy in as small an Airy Disk as can be achieved.

What a great way to show this. Thank you so much!

Edited by Eddgie (12/07/12 10:06 AM)


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5558965 - 12/07/12 10:11 AM

Eddgie, feel free to use that image, if in the future you find yourself trying to explain this again.

J


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5558991 - 12/07/12 10:24 AM

And I think I might add, that this is a great peice of detective work.

This can easily explain why these early observers saw what they saw, but back then, diffraction theory and MTF were not really well known, and optical quality was not I think as well understood. The answer was simply to build bigger and bigger scopes!

The artice that stated that tube currents could be the cause is unlikely to me because these people were very serious observers and I think would be famaliar with these issues.

What a fun tread this has been for me. It is such a powerful testimony to the beauty of MTF that perhaps it will encourage more people to want to learn about it.

I am sure a lot of people got really tired of my MTF plots, but they explain all of this with great precision.

And obstructed scopes, near the limit of their performance, actually have better contrast than unobstructed scopes!

In fact, the observer using a smaller refractor may have not seen this effect so easily and may have been more likely to see Io as just a point, where a reflector user using the same size instrument would have been able to detect (sorry Norme) that the disk of Io was not evenly illuminated simply because of the fact that it appeared elongated and a quick look at the shadow of a transit would show it to be distincly round. The only inescapable conclusion would be that the disk is not evenly illuminated!

But again, the peer reviewers back then would not have had this theory to help them determine why the observations yeilded the results that were reported.

But this peice of modern detective work I think is a clear and concise explination that is anchored in the concrete physics of diffraction and MTF.

I think this is a minor historical mystery that has been completely solved! There is 100% correlation between theory and the observations reported and seperated by many, many decades of time.

My humble opinion, but one of the best threads ever on this entire group of forums. I feel like we have contributed to history by solving this minor mystery.

Edited by Eddgie (12/07/12 10:26 AM)


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5559136 - 12/07/12 11:40 AM

Every scope transfers contrast, that's essentially what scopes do. The act of gathering light (or lack of light) and putting it on the focal plane involves the transfer of contrast (simply diffraction) from the target to the focal plane. That involves a good figure, etc., all the stuff we debate about performance. But, at it's core, it's all about taking an object and transferring it to the focal plane.

So, there is a level of performance that can be described by theory. Then there is actual performance that is not theory. In either case, the scope is performing to it's level of contrast transfer...it's MTF. Every time, all day, all night, from now until the end of time.

The MTF describes everything (or can, theory is all about concept rather than practice) that affects performance from diffraction, to CO, to aberrations, to seeing. The actual curve might not look like the perfect "textbook" curve on any given night, but it is always performing at a level of contrast transfer none-the-less. Always. That's what scopes do.

However, when all those variables (aberration, seeing, cooling, collimation, and the list goes on) are minimized, the scope's performance will be very closely matched to it's textbook MTF performance. And when that happens, look out! Superb views...

Anyway, I am a believer in the science of it.


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5559173 - 12/07/12 12:00 PM

Quote:

On Sept. 8, .189°, with the I2-inch this satellite presented a remarkable aspect while in dark transit. I noticed that it appeared elongated in a direction nearly perpendicular to the belts of Jupiter.




Ya! So, he saw it, too. And was not sure why, if only for a while. Fascinating, Jason, just fascinating. I think this exceeds reasonable doubt, and for the reasons Eddgie (and Pete, too, by the way) have always said. Such difficult observations are not impossible, they are within the laws of physics even if they (seem to) violate the old textbook standards of resolution.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5559229 - 12/07/12 12:36 PM

Yes, Barnard was seeing Io transit a light cloud band, and thus it was the dark poles he saw, making the relatively dark shape of the moon stand out, looking to be extended in the polar axis, as the equatorial region blended with the background clouds.

Further observations of similar transits against a light cloud band background lead him to begin to discern the 2 polar caps as individual objects, separated by the effectively invisible bright equatorial region.

Essentially, Barnard is describing a second possible aspect in which the Jovian background can affect the apparent shape of Io. On a light background, Io may appear only as 2 poles. On a darker cloud background, the poles blend and only the equatorial region stands out.

Rayleigh, Dawes, and Sparrow ("textbook" resolution limits) all concern separating point sources. The extended nature of Io, a gathering of infinite point sources, requires a examining the matter in a slightly different, though ultimately related, frame of mind. The diffraction effects for any one of those points remains the same, but they blend together to make the final image. The image is the sum of its parts.

We aren't breaking any rules of resolution, only refining our understanding of them.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5559410 - 12/07/12 02:30 PM

EE Barnard's follow up of the his Jan 8, 1890 observation is available here:

Barnard's report

I ran the PDF thru a quick OCR and reproduce the content here:

*********************************************************
On the Dark Poles and Bright Equatorial Belt of the First
Satellite of Jupiter. By E. E. Ba.rnard, M.A.

It will, perhaps, be remembered that on 1890 September 8, while observing the transit of the first satellite of Jupiter with the 12-inch equatorial, the satellite appeared as a dusky elongated spot projected on a bright region of Jupiter. With a high power it appeared distinctly double, on a line nearly vertical to the belts of J~6piter. I called Mr. Burnham's attention to it, and we both saw it thus for upwards of half an hour. Subsequently it was seen several times when crossing a dark portion of the planet as a bright, very elongated spot, but the elongation in these cases was nearly parallel to the belts of h6piter. Yet when closely examined on the sky it always appeared perfectly round.

An account of these observations will be found in Monthly Notices, vol. Ii. , NO. 9. To explain these singular peculiarities I at that time offered two theories: the first of these was that the satellite was itself possibly double. This idea has long since been abandoned because of its improbability. The second theory supposed the satellite to be surrounded with a white equatorial belt, and that its poles were dark or dusky, and that it rotated on an axis nearly pflrpendicular to its orbit. If such were the case, when the satellite crossed a bright portion of the planet the white belt would cut it apparently in two, as it would be equal in brightness to the surface of Jupiter, and thus leave the two dark polar caps as two separate spots nearly perpendicular to the belts of Jupiter, and would thus give the observed appearance of duplicity.

If, however, the satellite should happen to be projected on a dark belt, then the dark poles would merge into the surface of Jupiter, and the white equatorial belt alone would be visible as an elongated white spot nearly parallel to the belts of Jupiter.

It was not until this year (1893) that an opportunity occurred to settle this question with the 36-inch.

On September 2S last the transit of this satellite was watched with the great telescope. It first appeared as an elongated white spot, east and west, when over the dusky region near the planet's limb, and later it appeared as two dusky spots in a line north and south, exactly as it appeared in the lz-inch 1890 September 8. But during moments of good definition it was seen distinctly as a small round disc, dusky at the poles, and with a white belt between them.

On November 11 it was again observed under nearly similar conditions, and presented the same phenomena.

The best view of these dark polar caps and bright belt was had on November 19, with a power of 1,000 diameters on the great telescope, and almost perfect seeing.

At this transit the satellite partly obscured its own shadow on the south preceding side, and was partly projected on the southern edge of the south equatorial belt, and partly on the bright region beyond.

With the fine seeing the satellite presented a beautiful appearance. It stood out in bold relief like a little globe. The polar caps were heavi.ly marked and quite dark, while the bright belt was very conspicuous.

The observation was perfectly satisfactory, and the second theory had become a fact.

I send a careful drawing of the appearance of the satellite on this date, which will give a good idea of the phenomenon. The shadow was larger than the satellite.

We have here established the discovery made 1890 September 8 with the 12-inch telescope, that this little attendant on Jupiter has distinct polar caps that are dusky like those of Jupiter, and that it has a bright equatorial belt, as bright as the brightest portion of Jupiter's surface. The conclusion is uncontestable, therefore, that the satellite also rotates on an axis nearly perpendicular to its orbit, as Jupiter itself does.

From the fact that the bright belt is not always exactly parallel to those on Jupiter, and the line between the polar caps is not always exactly perpendicular to the belts of Jupiter, there must be a slight inclination of the axis of rotation of the satellite. From the fact also that the south cap is sometimes apparently a little smaller than the northern one, its axis is probably tipped away from us at its southern end. It is also probably tilted towards the west by a few deg-rees. From peculiarities in the appearance of the belt, it is probable that the period of rotation on this axis is not coincident with the satellite's period of revolution about Jupiter.

I have data in my hands now that will after a few more observations, perhaps, settle th.e inclination of the axis, and probably give us the period of rotation.

I think the presence of these dusky poles and bright belt would rather imply that this satellite at least is in a physical condition not vastly different from that of Jupitm' itself.

Mount Hamilton, California:
1893 November 27.

© Royal Astronomical Society • Provided by the NASA Astrophysics Data System
1894MNRAS..54..134B
**********************************************************

Again, today we have the distinct advantage of knowing that Io's rotation period does indeed match its orbital period, and its axis is virtually parallel to Jupiter's, but I can't help but be impressed by Barnard's careful observations.

I'd love to hear of others repeating this observation. It's quite achievable (hell, I done it!), and extremely rewarding. How small a scope can this be observed in? We've got down to 6" so far... My 4.5's incapable, I believe, but another might be able...

J


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Eddgie
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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5559796 - 12/07/12 06:42 PM

Quote:

The best view of these dark polar caps and bright belt was had on November 19, with a power of 1,000 diameters on the great telescope, and almost perfect seeing.




Isn't this quite interesting.

In "Almost perfect seeing" the best view of the dark polar caps was seen with a power of 1000 diameters.

Interesting that in an 889mm aperture this power gives an exit pupil of .9mm.

Hmmmm. How very interesting... Could have used any power they wanted on a night of excellent seeing, but they felt that their best result was with an exit pupil that I myself often recommend as being about the best exit pupil for planetary observing where the goal is to see the most detail possible in a view.

Funny coincidence. But I guess that is all it is. I mean they were using a refractor and everything, so I would have thought 1750 diameters would have been better because that would be about 50x per inch.

Yeah, maybe just a funny coincidence that in a night of almost perfect seeing, their best result was with a .9mm exit pupil.

I don't know.. Head scratcher I guess.


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Rick Woods
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5559804 - 12/07/12 06:50 PM

Quote:

Yeah, maybe just a funny coincidence that in a night of almost perfect seeing, their best result was with a .9mm exit pupil.

I don't know.. Head scratcher I guess.




Not at all.
You just have a good feel for the right exit pupil for the job.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5559885 - 12/07/12 07:57 PM

That's a terrific illustration. Clear to the point and how I envisioned it from the thread, notably Eddgies and Normed description. An interesting question would be WHEN does this effect disappear and the moon is merelly a circle hoar airy disc? I'm confident my 70mm could not pull offthis kind of thing even at 300x.

I'm going to guess based on Normed effort its conceivable maybe that a 5" aperture might do it?

The 1000 diameters for a 36" telescope being optimum compared to 50x per inch would sound about right for it on a night of near perfect seeing while 50x per inch would probably suite a 6" scope. I don't think that the power per in h rule is a constant with apertures of greater and greater size where the atmosphere plays a greater and greater role in compromising the potential for full resolution. At some point even near perfect seeing is going to prevent this as aperture increases.

Pete

Edited by azure1961p (12/07/12 08:34 PM)


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5560008 - 12/07/12 09:42 PM

Pete and Jason, in fact, Pickering urged amateurs to attempt it in 4 and 5 inch scopes! Why? Probably because he understood the angular size of Io would allow it. It get's increasingly difficult do do as Airy disc size approaches it's angular size. As the optical path difference drops to zero (each point is closer to the center of the Airy disc) strange things happen. At zero OPD, the Airy disc itself expands and brightens.

What's interesting, in the article one observer credited with resolving (sorry Eddgie ) a binary star at 0.2" arc in a 6" refractor also said he could detect no elongation of Io. One has to assume he was using a scope large enough to see the poles, then Io would indeed not be circular. But, that does not refute the observation that Io /appears/ elongated in some apertures.

Pete, this stuff is right up your alley. Jason, yes, we're not violating anything about Raleigh or Dawes. They define the limits of resolution as dark space between two point sources. This is not happening here, we are observing the effects on diffraction on extended objects. There is, of course, no dark space /between/ any of Io's points. There is dark space "around" them, however, which allows "detection" as one spurious disc invades that dark space. Everything Dawes and Raleigh say remains true. But, to call their work true limits is kind of misleading.

This is why the guy mentioned above could discern such a small 0.2" arc angular separation in a 6" refractor. I have a similar experience with elongating 72 Pegasi at 0.5" arc.

Edited by Asbytec (12/07/12 10:08 PM)


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5560193 - 12/07/12 11:56 PM

Damn does this mean I can elongate 0.1? Funny because 0.1 was the first sign of elongation I could detect with seeing-free aberrator. Boy that'd be a 9/10 night or nothing.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5560391 - 12/08/12 03:55 AM

Dunno, don't let Dawes stop you from trying.

But, you know, once you start getting that close, strange things begin to happen. Up to a point where optical path is very small, the PSF remains relatively normal. You might even be able to detect two stars directly on top of each other by noting the Airy disc increases in size, pushing the first ring outward a bit. As I understand it, anyway.

"Resolution of two stars in coherent light at 1.22Lamda/D angular separation varies with the OPD between two sources. At zero path difference, the two patterns merge together, forming the central maxima of 1.83LambdaF in radius and 1.47 peak intensity. At pi/2 OPD the combined pattern is identical to that in incoherent light, and at OPD=pi; the two 1.11 maximas are somewhat more widely separated, with the intensity deep between them dropping to zero (Sparrow limit), the latter two indicating significantly better limiting resolution."

http://www.telescope-optics.net/telescope_resolution.htm

Bold is my edit. I think that is what he is saying.

Edited by Asbytec (12/08/12 07:18 AM)


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5561528 - 12/08/12 09:22 PM

This thread has been very informative for me. I enjoyed reading the discussions here and the historical accounts. I would love to see the albedo features on Io during transit. I look forward to a night when the seeing is perfect when I can boost the magnification to the max. Maybe a trip to Mt Hamilton. BTW I did have the opportunity to look through the 12 and 36 inch telescopes at Mt Hamilton years ago. Thanks to the people who have contributed to this great thread. There is an image by DesertRat that shows the Io transit that happened last night which I saw in ok seeing. His image shows the dark poles that are contrasted by the face of Jupiter. The other image linked to earlier by Mike Phillips is an excellent image as well.

Great thread. Thank you everyone. Dean


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Re: Some thoughts on a Transit of Io new [Re: Dean Norris]
      #5561633 - 12/08/12 10:48 PM

Dean, glad you chimed in. This observation sheds new light on Jupiter. I bet you will be amazed when you get a chance to attempt it.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5562404 - 12/09/12 12:45 PM

Had to peek at Io again tonight. Very clear, pretty steady. Unfortunately, I have too file tonight's observation as inconclusive. Io would just not hold still long enough for a good look. Still had those moments where it appeared elongated, but just cannot rule out seeing as the cause. Both Io and Europa were just not steady for periods long enough to really make a call. But both in the same FOV for comparison.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5562615 - 12/09/12 03:05 PM

I don't think there is a solar system body that's able to reveal albedo effects that's more seeing demanding than Io. Little tremors in seeing that might gently soften the planets temporarily obliterate everything . I envy hour views regardless based on your description elsewhere.

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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5562773 - 12/09/12 04:52 PM

You can bet, gonna keep that one on the list.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5563855 - 12/10/12 10:00 AM

Well, I am totally sold. I do n0t care what anyone says, Pickering's and Barnard's observations can be repeated in a 6 or 8" aperture. Io is just barely elongated, even against the black of space. It takes very excellent conditions to pull it off in a 6", but it can be done. Period.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5564036 - 12/10/12 12:01 PM

I'm sold too (ya know, what with having seen it in my own eye and such), though I long for a repeat of that first night's conditions so I can see it again. I've had the scope out only 2x since then, both days with 5-20 arcsecond seeing, so no chance.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5564063 - 12/10/12 12:17 PM

Jason, now if other's would just do it, make it common knowledge. Eddgies "pearl" comment and your thread opened the door to nudge visual observing into a better place. I just hope my own observations put down a door stop to keep the door from slamming shut. Great thread, one that made a difference for those who care to observe such things. Scratch one more boring disc from the list of boring discs.

Edited by Asbytec (12/10/12 12:19 PM)


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JasonBurry
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5564117 - 12/10/12 12:56 PM

Boring disc? What's that? Never seen one without its own charm and character....

I think that between you and Eddgie, me and historical accounts from EE Barnard, it's a hard door to shut now.

There are hundreds of amateurs out there with scopes far more capable than the 12" Lick refractor thru which Barnard made his initial observations.

Here's how I see it. In a Victorian refractor, Barnard saw well enough to be CERTAIN of the non-plain-ness of Io, enough to write about it quite extensively. Enough to be willing to wait 3 years to follow it up in the great 36" scope.

That's seeing something unknown.

We, today, have an advantage. We KNOW Io's disk isn't plain, even if it is on the edge of the capabilities of a 6, 8, 12, 14" scope. Knowing to look for a feature is a great advantage. I noticed it, in part, because I'd been puzzled by the football aspect of Io in astrophotos, combined with a fortuitous night of spectacular seeing.

This thread creeps up on 100 replies now. It's been top-of-list on this forum for 2 weeks. Others now know of this. They may not make it their mission to observe non-circular Io transits, but it'll be stuck in the back of their minds. One day, the seeing will work, the "dash" will appear, the memory tweak...

Others will observe. We'll see reports. Eventually. It took Barnard 3 years to confirm his observation.

J


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5564591 - 12/10/12 05:48 PM

My wish is that it would generate more general interest into how contast transfer (which is very much affected by diffraction caused by the size of the aperture and the obstruction (if present).

Everything on this thread to me was a 100% validation of the theory of MTF.

I just don't understand why more people aren't interested in this topic. It is like the ultimate question from Hitchhiker's guide or The Truth is Out There from X Files. It explains it all. To understand MTF is to understand how telescopes work, and what a given instrument can and cannot do.

A wonderful thread though.. I was excited when somone else saw my lovely Io Pearl. I felt like I shared a special little treasure with friends.

And maybe more people will look for this little jewel now.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5564711 - 12/10/12 06:55 PM

I'm having Thursday purposely off to facilitate some astronomy. It's been a stretch of *BLEEP* weather since thanksgiving. It's gonna rain all the way till wednesday. Started yesterday rain all day today and prior just clouds clouds and clouds and patchy sun.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5565084 - 12/10/12 11:12 PM

Agreed with everything said above (cuz lunch is ready.)

I'm pulling for you, Pete. You gotta see this if the weather holds. You can repeat Barnard and Pickering! To me that's exciting.


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Re: Some thoughts on a Transit of Io new [Re: Eddgie]
      #5566452 - 12/11/12 07:01 PM

Quote:

My wish is that it would generate more general interest into how contast transfer (which is very much affected by diffraction caused by the size of the aperture and the obstruction (if present).

Everything on this thread to me was a 100% validation of the theory of MTF.

I just don't understand why more people aren't interested in this topic. It is like the ultimate question from Hitchhiker's guide or The Truth is Out There from X Files. It explains it all. To understand MTF is to understand how telescopes work, and what a given instrument can and cannot do.

A wonderful thread though.. I was excited when somone else saw my lovely Io Pearl. I felt like I shared a special little treasure with friends.

And maybe more people will look for this little jewel now.




Well who's dissenting?

Pete


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5566497 - 12/11/12 07:44 PM

Norme, I'm late to this thread - a very interesting one, and I'm impressed that the "Io effect" can be seen with a 6-inch - but I'm wondering about your suggestion of an observer who saw a 0.2" double elongated with a 6-inch telescope - who was that? SW Burnham?

I'd believe it with a 26-inch telescope, no problem; but a 6-inch? The best figure for SW Burnham, listed in Lewis's discussion of double star resolution in 1914 - yeah, that paper again - is Burnham managing 0.4" with a 6-inch (and 0.35" with a 9.4-inch).

Sidgwick seems to be the source for the 0.2" claim, but I haven't been able to find the source for this claim. And was it just one example? - so we'd need to know the separation of the pair at the time, and as a "one-off" whether it was a lucky guess, and why it didn't happen again.

The work by Christopher Taylor with a 12.5-inch scope on extremely close doubles, where he's recorded detectable elongation down to the 0.17-0.20" range, suggests that somewhere closer to 0.4" might be a better fit for Burnham as well.

I've seen detectable elongation at 0.50"-.53" with 14cm aperture (several pairs) - visible at 400x, confirmed at 570x. I'd suspect that under excellent seeing 0.45" might be possible with 14cm. An analog of Taylor's achievement would be 0.40" with 14cm - I did try one pair at that separation without success, and plan to try again if I can get a steady night and a suitable pair. Taylor may have excellent "out-of-round" eyesight, which is needed with such images (even at the 825x he uses). Extending Taylor to a 6-inch would suggest 0.37" as a limit.

So I have difficulty believing 0.2", even for Burnham. He was a remarkable observer but I don't believe he had to avoid kryptonite.


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Re: Some thoughts on a Transit of Io new [Re: fred1871]
      #5566584 - 12/11/12 09:11 PM

Fred, from the S&T article (posted above, but removed from the link), it was Burnham. He, "once correctly identified a binary star separated by only 0.2 arcsecond using a 6" refractor."

Anyway, the article mentioned he was so good at noticing elongation, yet he could not observe any on Io. Apparently he was looking at the full disc trying to elongate a circular disc. Io is not elongated in this way. The article did not say specifically what he was looking at, but I think that has to be the case. It also mentioned they could see the bright equator that would explain Io's apparent elongated effect seen by Pickering.

Io is still tiny small disc in my 150mm, but it has an aspect (best I can tell) near or a tad less than elongation seen in 72 Pegasi at .57" arc using 380x in excellent seeing.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5566602 - 12/11/12 09:23 PM

I've not yet tried for a double closer than 0.5 with an 0.576 res scope but from the way 0.5 looked on several doubles I'd wager I could probably see an overlapped diffraction pattern or elongation of equal brightness somewhere between 0.4 and 0.3 arc seconds. It's projection as I haven't done it but 0.5 wasn't that hard in 7/10 or better seeing even when magnitudes were asymmetric.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5566868 - 12/12/12 12:50 AM

Makes sense to me, Pete.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5566974 - 12/12/12 04:44 AM

Norme, what issue of S&T was the article in? - I can't find it in my DVD set.

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Re: Some thoughts on a Transit of Io new [Re: fred1871]
      #5567017 - 12/12/12 05:42 AM

I'm sorry Fred, I should have included that information.

"The Story of Jupiter's Egg Moons," by Thomas Dobbins and William Sheehan, Jan 2004.

If you cannot find a copy, I can email it for personal use without violating copyright.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5567099 - 12/12/12 07:48 AM

Thanks for the information - that'll be on the DVD set of S&T I have. I was looking in the 1990s issues because of the earlier reference to an item on Io back then.

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Re: Some thoughts on a Transit of Io new [Re: fred1871]
      #5567714 - 12/12/12 02:25 PM

It's a nice article. If it was pulled off the Internet by Sky as it used to be up, Id say it was a bad marketing move. Here's a great example of a single article playing into the needs of the amateur and broadcasted on the biggest amateur astronomy website on the Internet. For all that exposure and the paltry sim it cost anyone it was great PR underscoring Sky's "essential" need to the observer.

But perhaps they didn't pull it and its gone for other reasons. Regardless it was great promotional marketing for the mag and for free.

Oh well.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5568009 - 12/12/12 05:45 PM

Yea, silly board rooms.

Actually, I'd be interested to hear Fred's reaction if he repeats the observation. I got a slice of humble pie riding on it and my fingers crossed.

Observed Io last night and place the result in the "pretty sure" category.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5568769 - 12/13/12 07:38 AM

I've been directly under the jet stream the last week or so, and so it will continue. Bugger. One day!

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5569071 - 12/13/12 11:32 AM

ok clear skys tonight, 39F - finally and on a night off [that i created] . Ill do my best with Io and drum up a jupiter sketch to boot. Particularly im going to see what i can do to kill the dew on my oculars when observing. Im going to fabricate something today.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5569164 - 12/13/12 12:27 PM

Pete, try keeping them in your pocket. Good luck with Io, I look forward to your report.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5569169 - 12/13/12 12:32 PM

That's what I do... Eyepieces in pocket till time to use'em. It has worked for me down to -20C.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5569385 - 12/13/12 02:33 PM

Reading up one the difference between point sources and extended objects, came across this interesting piece. Apparently, there is a limit to how small an extended object can be and still produce a PSF very similar to that of a point source. Io is a good example, and so are the individual chunks that make up Saturn's rings as seen edge on, as Pete mentioned in another thread. I'd say those chunks are well below the 1/4 Airy disc diameter in modest apertures and qualify as point sources.

It appears that angular size is given by 125,000 Lambda/Dmm. So, for D = 150mm and Lambda = 0.00055, anything smaller than 0.46" arc (~1/4 the Airy disc at 1.82" arc) is essentially a point source with no appreciable widening of it's PSF.

Io is well beyond that limit at 1.2" arc. It's image radius changes from 1.22 Lambda F for a point source to a little larger than 2 Lambda F as an extended object (with a apparent angular radius of a little more than half the Airy diameter.) Ganymede is nearly the same angular diameter of a 150mm Airy disc (~1.8" arc) and shows a disc a bit more than twice the Airy disc size at 3 Lambda F (~/> 2 * 1.22 Lambda F radius for a point source.)

http://www.telescope-optics.net/telescope_resolution.htm

I think this is just further proof one can see elongation in about 6" or more aperture, since Io's apparent diameter is well beyond that of a simple point source PSF or an extended object 0.46" arc. It would be very much like elongating 72 Pegasi at 0.57" arc separation. Although, Io is indeed more challenging.


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fred1871
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5569804 - 12/13/12 07:33 PM

I've now read the article on "Jupiter's Egg Moons" - very good, and a nice portrait of Pickering as an eccentric observer. No surprise that he teamed up with Percival Lowell.

I'll make an attempt on the "Io effect" though Jupiter isn't well placed for high resolution stuff from where I am - it's at nearly its highest declination north, and I'm in the below-30 latitude region, so it doesn't rise as high as I'd like. I did have a look at Jupiter the night before last, and although seeing was very good in some parts of the sky, it wasn't good enough around Jupiter to see Io as more than a small disk off the planet. I could use 285x, but 400x was wobbly. Elsewhere in the sky I used 400x on some double stars with good effect. The moons were of obviously different sizes. So I'll try again, preferably with Io in transit. Best chance for the elliptical look.

On the claim about Burnham and a 0.2" double, no new information there. I'm now working my way through his General Catalog of Double Stars to see if I can identify the claim. With a number of these he remarks that he suspected a star double with the 6-inch refractor, confirmed later with larger (18.5 or 36 inch typically) scopes. Also a few where he suspected a double but couldn't confirm even with the Lick 36-inch. Once I have the list of possibles, I'll check out the measures list. A couple of these appear to have good orbits established, so a pretty accurate figure for when he first suspected them to be double can be obtained. Along the way I've found a few that fit Lewis's data collection - around 0.4". Very impressive for 6-inch. In a couple of places Burnham remarks on pairs around the 0.2"-0.3" level as being a challenge with larger telescopes.

I'll do a note on this when I've completed it, probably in the Double Star forum. Perhaps with a reference note to it in this thread.

Now, if the clouds (back again) will clear sometime soon, despite the weather forecast of days of more clouds ....

Edited by fred1871 (12/13/12 11:52 PM)


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Re: Some thoughts on a Transit of Io new [Re: fred1871]
      #5569992 - 12/13/12 09:33 PM

Fred, have been quietly following the rule of thumb thread, if that's the one you mean.

From the math above, I am wondering if somewhere near 0.4" arc (about 1/4th Airy disc) is at or near a limit for the 6". Below that separation seems to be the realm of point sources. According to the math, anyway. Curious...but seems consistent with some observations you mentioned.

I am at 16 degrees North and Jupiter passes pretty much through the Zenith. In our tropical climate upper air flow from the Pacific Ocean is pretty much laminar, the 6" really hits a sweet spot here. The first diffraction ring is nearly always visible and very steady much of that time. It bounces around from time to time, but generally it's very nicely presented.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5570075 - 12/13/12 10:31 PM

The first diffraction ring in ct is cause for a gazzoo.

Pete


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fred1871
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5570172 - 12/14/12 12:01 AM

Sounds as if you've got near-ideal conditions for high-res visual images, Norme. I don't get the laminar airflow, being somewhat inland from the wrong (east) coast. And Jupiter's rising only a bit over 30 degrees from my horizon.

Yes, I'd think 0.4" might/should be possible with 6-inch scope, as Burnham and a few others have seen elongation on even pairs at that separation. It also fits Christopher Taylor's experience, scaled from his 12.5-inch.

I'll make attempts on Io as weather allows. Should be interesting. I'm inclined to be doubting of Pickering's claim re 4-5-inch telescopes, but as I have a 5.5-inch (140mm) and it's a refractor I'll see what's possible. I've been surprised before by seeing things I'd thought needed a bigger scope.

Re Pete's last note - ummm, not sure what the slanguage means.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: fred1871]
      #5570226 - 12/14/12 12:56 AM

As the other post mentioned, I can confirm with you folks on Ios egg shape. Europa near it made the comparison clear - on color too. Nice pale peach on Io and a nice pale yellow for Ganymede. Europa just appeared off white. At anyrate Europs tighter and symmetrical circle-dot made for good contrast to Io s Egg look.

Never never would e seen had I not specifically looked for it. Confirmed at 364x.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5570275 - 12/14/12 02:59 AM

Fred, I have been literally stunned at what good seeing can allow. Six inches of aperture does not disappoint in the least. I would be pleased if you got stunned by Io, too. We can all add that one to our growing list of stunning sights, even if Pickering was, well, wrong about other things.

Pete, exactly. If Europa is in the same FOV, the comparison get's easier. Europa is the definition of round and there is no question, no doubt in my mind it's round. Io ("effect") is reasonably questionable in comparison. Sometimes it just hits you as elongated during the best moments. Over the cloud tops should be much easier.

So glad you caught that, Pete. You're part of a growing alumni. And you're right, you never would have noticed it at 30x per inch observing Jupiter.

Still trying to understand Io's extended nature and why it's difficult to see elongation visually a 1.2" arc - more so that 72 Pegasi at 0.56" arc, for example.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5570398 - 12/14/12 07:18 AM

That is a good question.

Pete


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5844954 - 05/07/13 06:08 AM

Quote:

Eddgie, maybe this will help your explanations. I'm a CAD operator in real life, and I used CAD to do a rough simulation of the diffraction effects involved in our observations of Io. I humbly submit it here for discussion. This models an 8" telescope with no CO, giving an Airy disc of 0.68". I've laid multiple airy discs over a grid laid on the face of "Io", with equatorial region discs shown bright, and polar discs shown darker.

It's a good likeness to what I observed, allowing for my crude simulation.

J




Hi Jason,

Reading through this in another link led me to question the diagram
you attached. While I agree with the diagram in principle as to how diffraction defines a small orb like Io through an 8" scope it would seem its also exaggerated heavily. The image of Io would infact bloat like that beyond its physical apparent size if it had the surface brightness to fill it out like that. This diagram works better when the target is a star for example where its surface brightness is exceedingly high . Then if you had a point source like a star now filling in the size of IOS apparent size with all those infinite points it'd be dazzling. Infact it'd be so bright you wouldn't want to look at it and if you did it would indeed be bloated glaring and soft edged.
Such as it is those per infinite point Io is far dimmer and doesn't swell as you've shown.

The diagram does show how the ovular shape is affected by diffraction and the lesser surface brightness on the poles but its misleading to . I'm convinced at Ios brightness level there is no swelling visible beyond its observed physical size.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5845640 - 05/07/13 01:38 PM

Its a good question, Pete. I was reviewing Vald's explanation of point sources...how big they have to be to start expanding the Airy pattern. Turns out, about 1/4th the Airy disc diameter offers a point source PSF. Any bigger, then the edge of the spurious disc begins expanding markedly.

Now, at Io's angular diameter near opposition, it's well over 1/4 the Airy disc diameter. It is, indeed, an extended object with an enlarged PSF. But, how it behaves is very complicated.

I'd have to review Vlad's site, again, to speak to the question. But it does seem it acts as a series of point sources (1/4 x Airy diameter), some of which are brighter than others. After all, it's "football" shape does show very well in images for a reason (contrast and diffraction, I'd imagine.)

I'd like to know more, too.

In fact, I was just reading Sidgwick, he mentioned the apparent elliptical appearance of Jupiter I (Io) and 4 (Callisto.) Not sure what that's all about...LOL. Let me find and reread his statement.

Edit: found it. Sidwick's Amateur Atronomer's handbook, section 26.10, Scales of Seeing, subparagraph (b), page 465. He describes one of Pickering's seeing scales, the "eliptical outline of Jupiter I and IV" that disappears in large enough telescopes. Remember, he urged amateurs to observe Io with a 5" glass, so that is probably the aperture range this seeing scale is intended.

Jupiter IV is Callisto! Who's game? LOL


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5846710 - 05/07/13 09:53 PM

I think Callisto is a case that's a lot like the canals on Mars. First there's a few detached markings, a mistranslation and all over the globe people are seeing canals. With Io we have it so much like the contagious canals spreading like a virus so too, the Galilean moons all suffered the same fever and Pickering and his pal getting each other worked up over it - though on a much smaller scale. Its sobering how expectations can fuel results that are completely false and with fervor.

I'm still undecided on the Io - is it the real limb or diffraction. I mean what if the poles are just merely too close to the background sky glare to show it seperated and whole disc? I'm straddling diffraction and contrast here with question marks. I know they are intertwined but still .

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5846881 - 05/07/13 11:20 PM

Well, I dunno if it's real limb or diffraction, either. That's what I want to know.

You may be right about fervor and seeing Io as an elliptical orb. Still, I do believe I observed it. Of course, it is not obvious. It is difficult. It did require stable seeing and maybe it even required fervor to undertake such a difficult observation. So, fervor might have been an attribute, not something creating an illusion. It really helped to have Europa in the FOV for comparison. High power was a big help, too. But, sure enough...with patients and fervor (lol) it can be done.

Now, how and why are still a bit of a mystery. I believe it is diffraction effects, as Eddgie says. Io is small enough, still, to be dominated by it. Ganymede, in my 6" scope, is right about the angular dimension where it begins to become a true extended source. It's PSF is greatly expanded at opposition.

I'd have to review Vlad's take on this point source and extended object boundary. It's complicated, but that doesn't mean Io's elongation is any less real.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5847258 - 05/08/13 07:45 AM

No no no - Norme in the case of Io - a lot of us observed it (I don't - maybe just several this is a fairly under wraps thing it would seem). My contention is that in the case of Callisto that was erroneous with Io kicking it all off and the mind having at it. Io was real Callisto and other moons by Pickering was him and his buddy running away with themselves.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #5847297 - 05/08/13 08:27 AM

LOL, I agree Pete.

Also, my "simulation" is extremely crude. I'm sure it falls short on many levels.... My understanding of diffraction is limited.

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #5848079 - 05/08/13 03:59 PM

Ah, ok, Pete...ya, I agree on Callisto. You got me rethinking the whole Io thing, I didn't understand your question, I guess. However, Callisto has become more interesting...LOL

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #5860424 - 05/14/13 05:05 PM

Does it actually look football-shaped? Or just slightly out of round? If, as 1 or 2 people said, that Io looked darker near the poles, couldn't that make the top and bottom less visible, thus making it look flattened and oblong slightly?

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Re: Some thoughts on a Transit of Io new [Re: Classic8]
      #5861108 - 05/14/13 10:28 PM

Its slightly out of round and you need, or it certainly helps to have Europa nearby in that its a great comparator . Io is evvveeerrr so slightly depressed or tad flat at the poles in appearance. When you do see it its a very certain thing - just very subtle.

Pete


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Re: Some thoughts on a Transit of Io new [Re: Classic8]
      #5861618 - 05/15/13 08:17 AM

Classic8, yes, exactly, especially when Io's in transit in a dark cloud band... The poles blend into the background, leaving the brighter equatorial region only showing in modest instruments.

I've not seen the effect with Io not in transit, though Pete (and doubtless others) has, and for that case, having a round reference (Europa) in view really helps with the comparison.

Good luck!

J


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #6351419 - 02/02/14 02:55 PM


David Knisley posted the following . Because he commented as well the lunar forum was not the place for this topic Ive transplanted it here. Here's what David had to say:

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.

--------------------
David W. Knisely . . . . . . "If you aren't having fun in this hobby, you aren't doing it right."

Hi David,

Just to be clear Im not suggesting Ive seen dark poles on Io or anything on Io infact and up until I made a concerted effort a year ago or more Id never noticed this moon as anything but a round 1" dot. In inspecting it at over 300x with the information put fourth in this thread I gave a look see. At first it was just well, a golden warm toned dot indeed. Studying it though it was conceivable how it could be seen to appear somewhat full around the belt line, ie; equator. It was one of those hmmm moments. What clinched it was Europa just next to it and granted the sizes are slightly different but the circularity of Europa gave away this subtle oblate nature of Io that had been discussed. Had Europa been behind Jupiter I may have said " undecided but suspicious of oblate nature" or something to that effect . Io appeared rotund - a strange word for a round body but that was the knee jerk impression. Its fullness was the effect of its brighter middle averaged out with its darker poles as ever so slightly ovular. The face of Io was blank as always - its profile was in question here. By contrast it never showed the hard perfect roundness of Europa.

I don't doubt on 46 years its never been but a dot and had I not tried on a decent night it'd be another 46 for me (actually 30).

The experience you have had with some very large aperture wouldn't be revealing here because the oblate profile is a diffraction effect of medium aperture. At 14" Ed Moreno had agreed the disc would appear round and not oblate because by that point the angular resolution and contrast would be sufficient to reveal Ios truer spherical nature. If anything David something like a 6" off axis mask would be revealing than large aperture because you'd be introducing the lower resolution diffraction effects responsible here. Timo as well as Sheehan, Pickering, Barnard all have realized greater aperture does not show the ovular profile but it was never a physical attribute of Io to begin with.

I would say this - if you get a night of 6-7 Pickering and stop down your scope to 6" , use at least 250x and time it with a close grouping if Io and Europa and Im certain you'll see the effect. The moon will be forever blank but its profile will appear, again, slightly rotund. A low res diffraction effect.

I appreciate you as a very careful, informed and responsible observer but I KNOW you'd see it under the suggested conditions. This is a call that needs a "control" close by to make a confident call.

Pete


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David Gray
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6352666 - 02/03/14 07:40 AM Attachment (8 downloads)

As I am coming in on this (a little against my better judgement!) but just get this out of the way:-

In the first place I do not think I/we are getting anything more than indications of real features on these bodies with our ‘backyard’ scopes. For myself I am not trying to supersede NASA mapping . Simply satisfying that curiosity of what is presented at borderline contrasts/resolution i.e. a bit of fun – no pretensions/delusions of doing great things for science…….!

In actuality I have done less than a dozen drawings showing detail on those moons – not counting in-transit efforts since my first attempt in 1965. None of the former have I ever submitted to the BAA Jupiter Section to which I have contributed since 1969 when W.E. Fox was in charge. I have seen/suspected such detail on many nights: 1964-78 10” f/8 Newtonian and ’78-on with the 16.3” D-K but only very occasionally do I go for a drawing. In particular I find some Ganymede-features quite contrasty with x365 and that can lure me to check out the form of these with more magnification.

John Rogers makes no bones about his position on such drawings; though he is more acceptant of views of transits and such. In fact on page 326 of his book “The Giant Planet Jupiter” he shows a number of Io transit views including one I got in 1989. An SEB fade was in progress at the time and offered an ideal light, near-featureless, backdrop which allowed me to get darker poles and a duskier f. side of the satellite.

I have to confess I never really checked for any elongation with Io until I saw mention by Norme & Pete. What I report here does not contradict their impressions at all. But I further got the impression that the major axis of the apparent ellipse does not always line up with the angle of Jupiter’s belts being (so far) seen to vary as much as perhaps +/-20º. This subject to further good views of course. In keeping with their practice the other satellites are checked for any out-of-roundness. No astigmatism was apparent with myself or the optics – easily checked by rotating the viewing angle or the eyepieces.

Norme is aware of some of my above-mentioned efforts as I show with this PM I sent him on Jan. 14.

Sent to: Asbytec

Hi Norme,

I’ve been caught up with more ‘90s Saturn reporting – 86 dates this time so have stepped back somewhat from CN as I don’t want to look as though I’m ignoring folks…! So herewith a PM that I resisted putting on your thread.

Had a look at Io on Jan 9 (19:25-50 UT) & Jan 11 (20:45-21:40) and I am very assured of the elongated aspect on both dates. Certainly with a 6” off-axis on the D-K (x365 - binovu & x415-monovu). Not only that but also with the full 16.3” when the image is dimmed suitably – apodizer, filters and/or thin cloud. Further I find that the elongation major axis on these dates is not in line with the Jovian belts but slanted some 20º say toward p.a. 110º-290º: consistently – other moons looked quite round.

Further to that I find it is more marked in green filters than any other which suggests that the reddish polar caps are indeed the culprit.

I really need better seeing to follow-up however as on these dates with more ‘normal’ seeing. I find it a little peculiar in that I’m getting Pickering 6-7 with my focus-check- double Eta Gem (BU 1008); and the moons themselves come to that – but Jovian features relatively ill-contrasted for Antoniadi III/II-III!!

Maybe a project here into following apparitions and perhaps use such as WinJupos to plot against Io-CM when enough observations to hand…..

Also got a light polar region with Ganymede on the 11th with both apertures.


Dave.


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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6352710 - 02/03/14 08:28 AM


David,

Thanks for the account and kudos to Norme for keeping this under wraps!!

Its interesting that you see the brighter equatorial region offset at an angle differing from jupiters belts and to that end - well that's high res for you. Interestingly I never considered using filters - but at 8" while I can see ios color Id wonder if it'd stand up to a 58 green I have. A curious thing is I actually saw an image in one if the links that was in the Plato thread that does infact show the offcenter limb brightness of Io - both as it sits with Jupiter as a back drop but to a decidedly lower res image after it regains the backdrop of dark space.

Any chance you can qoute Rogers feelings on submitting drawings of the moons? I'm guessing his feelings are its too wrought with poor seeing effects and such and tough to do reliably.

I've got to get the book. Nice post David and thanks for weighing in.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6352854 - 02/03/14 09:47 AM

David, I am simply floored by your work.

Yea, this is not ground breaking science to dispute NASA, it's just an observation other amateurs can enjoy. Add one more Jovian moon to the list of exciting moons. Something to extend common knowledge in the amateur community, a challenging observation for us to get excited about and check off.

Long ago, Pete pushed me toward Ganymede. I thought there was no way, can't be done. Too small, diffraction resolution, etc. Turns out, it can be done...that was exciting. Its observations like this that keep it interesting.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #6352991 - 02/03/14 10:58 AM

Thanks Norme/Pete.

I hope to develop further on these issues shortly!

In the meantime I have a very good view of M82 & SN from last night to get on the PC for Sketching Forum. But a vile stiff-neck/headache at the moment.

Fun. Fun. Fun!

Dave.


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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6354479 - 02/03/14 10:13 PM Attachment (22 downloads)


Guys here's a sketch I made from the best night I had in seeing Ios diffraction effect through my 8" - 364x and Pickering 6 seeing and some patience in December 2012. Io on the left and the control being nearby Europa on the right - though much farther apart in real life of course. Naturally for me the face is bald but ever that diffraction swell across the equator.

Pete

Edited by azure1961p (02/03/14 10:15 PM)


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6354605 - 02/03/14 11:25 PM

Pete, that's amazing on many levels.

First that's about the apparent and difficult elongation I observe - just barely non round. That David can quantify and determine an apparent position angle it is nothing short of astounding. Such might be beyond me, but I didn't think to try. It was all I could do to see apparent elongation.

Second that you (and David) did it in Pickering 6 means so many others should be able to re-Pete (LOL) your observation. I managed it in Pickering 8 and that means I am just normal, I guess, not a super human observing machine, after all. (Meaning being one is not required to observe it, but it does take some care not to miss it.)

Now, Imagine the scene with both Ganymede with it's surface albedo and Io with it's elongation in the same FOV. I had that view a few weeks ago, it was simply beautiful.


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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #6355012 - 02/04/14 08:08 AM

Yes I recall that. I found the Io oblateness a much easier thing than Ganymedes shadings which takes the best seeing Ive got which means forget it till its at least late spring which means its few years away!!!! Io is a lot less conditional. I could luck out with the seeing but that high a Pickering value in winter?????? Hasn't happened in years. The boundary fan could offset that a bit but its still years away for me I think. Yeah that's the northeast.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6357072 - 02/05/14 07:09 AM Attachment (14 downloads)

Regret delay getting back here: that neck/headache thing lingered all through most of yesterday – observing hangover from Sunday night! So the M82/SN drawing to PC work was aborted – still what is a mere galaxy against a major moon of Jupiter…..

Firstly to address Pete’s fine graphic of Io v Europa roundness. Much as I find, the apparent ellipse hovers close to the profile of Saturn’s globe which turns out to be ellipse #1 in my comparison graphic.


I think a further test is to put the line of the eyes at 90º to the initial ‘horizontal’ sighting which should exaggerate the major axis relative to minor. This, assuming it is a common illusion as I detailed to Norme in his Ganymede and Io thread.
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6297950/page...

“Perhaps the elongation is greater than thought? If I recall/understand right our visual system causes us to see vertical dimensions taller than they really are. Looking at a Jupiter ellipse (BAA 64x60mm) or Jupiter itself and turning it 90º demonstrates this markedly - to me at least.

Similarly with Uranus' near n/s equatorial aspect this still causes me to see it as quite oblate - as the increasing tilt is now starting to equalize(circularize) polar & equatorial axes.

The 'Jupiter' graphic hopefully demonstrates - tho' individual monitor's aspect ratios might come into play.......!”


I have taken the liberty to use Pete’s graphic to further demonstrate with the attached.

Of course if this illusion is universally apparent; then using a true circle (Europa) works for us as the vertical axis exaggeration effect then gives added contrast with the compared object’s X-axis. Assuming most of us get this illusion, a monitor that has perfectly adjusted aspect ratio should show a circle as having a greater Y-axis. Actually I initially found that effect quite troublesome/irritating when first using such as Corel Draw – my perfect circles always looking a little ‘horizontally-challenged’. The way around it was to hold some object of known true/measured circularity against the screen as a check – more troublesome in the CRT days!

As I already indicated it is to my discredit that I failed to ever notice Io-elongated as Pete & Norme have done. Perhaps it is where my approach to observing went against me: where I endeavor to look on an object rather that at it – failed to see the form of the tree whilst seeking scrutiny of the leaves!

Dave.


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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6357837 - 02/05/14 02:35 PM

No discredit at all David. The fact is I doubt I ever would gave seen it had I not read the article and indeed, Jason Burrys thread which we are now in. I never for the life of me even entertained the idea of checking such a thing and its just minor enough its so easy to overlook. I too see the illusion of the flipped moon appearing more elliptical that way than horizontal. This is where having Europa nearby as the control in this visual comparison is invaluable. I will say however with my dobsonian mounted reflector the north and south poles are right and left and Jupiter appears to come in through the top of the FOV and drifts downward till its out of view - such is non tracking . All this to say that with this orientation seen of the Jupiter assembly the north and south poles if Io actually appear horizontal south being left and north right so my optical illusion effect is working against seeing the ellipse!!!

This'd be such a difficult affair if Io was jupiters lone moon.

I had no idea that the illusion of the flipped ellipse was so striking. I never knew the phenomenon even existed. Thanks your reply and illustrations.

Pete


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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6358002 - 02/05/14 04:06 PM

Pete not sure where I saw info re. this vertical-illusion - it maybe something to do with ideal aspect ratios for framing pictures that I read somewhere.

I too have never used tracking; the mount is fitted for it but never got round to getting it to work right. In fact I feel that letting the object drift across the field discourages fixated staring. Since getting the Meade 5000 Plossls I find I have an excellent virtually undistorted AFOV of 60º, ideal for drift-across views! But even with the lesser fields of my excellent Zeiss 16mm & 10mm Orthos. I find no hardship even when Barlowed to over x1000. Also the 28º of the Monocentric at x485 is manageable - the hefty rock-steady well aligned mounting being crucial here!

I know what you mean about Jupiter coming in at steep angles. The Amici (erecting) prism does that with single eyepiece views but not with the binoviewer which pretty much shows how it is in the sky no matter where the Amici is rotated to; in my experience at least.

Dave

Edited by David Gray (02/05/14 04:10 PM)


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6358739 - 02/05/14 11:26 PM

Dave, what can I say? You know, this observation and your introduction of the above illusion is just a wealth of knowledge and understanding we can all benefit from. I see illusions from time to time observing Jupiter, they are out there and we should recognize them if at all possible. Again, thank you for introducing the illusion. It does not discredit in any way, I think it enhances the apparent elongation observation - maybe it should appear wider than it did to me. Maybe the illusion kept is from really looking dash like. In any case, putting the two together is part of the puzzle of why Io looks the way it does.

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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #6359140 - 02/06/14 07:00 AM

Thanks Norme, Pete also: its good when we can get an illusion-effect to work for us in this way!

I always liked, to me, the aesthetically-dynamic look of Jupiter when highly inclined in the field of view. Part of that being the more evident presentation of it’s oblate figure. There is a further advantage, to some at least, in that when it is more perpendicular to the eye-line it can make very faint belts more certain. Nothing to do with the vertical-effect/illusion as far as I know. It was something old-time observers used to use as a check; tho’ some found no gain. It certainly works with me to a good degree; but using the binoviewer a lot now I do not get to apply it so much – always a trade off!

As I said previously I have some things re. the Jovians etc. that I may post, but possibly somewhat off-topic here. Not sure if to go to your recent “Extended Object Resolution” or start a new thread. Anyone who has Peek’s “The Planet Jupiter” (1958) and looks at chapter 32 might get a hint from where I’m coming.

When next apparition kicks off we have again the opportunity to observe mutual satellite phenomena. Peek’s book has some things to say regarding the visibility of, in particular, Europa’s shadow on Io & Ganymede and goes on to ‘prove’ that failure to see these stark black spots in amateur scopes is pretty damning against albedo drawings with these. I recently investigated his reported dates of Phillips and others impressions with WinJUPOS and get the impression that Peek greatly underestimates the darkness of the penumbra thus rendering the black umbra/spot very much less contrasty. Not that I take WinJUPOS simulations that literally without further inquiry; but clues are there!

Having said all that maybe another thread is in order and could be regarded as a preliminary to the coming satellite events but in addition alluding to what has been mentioned on these recent threads.

Cheers,
Dave.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6359220 - 02/06/14 08:21 AM

I think Peek, as you say, greatly underestimates the visibility of these shadows in amateur instruments. A CN member , Buddy Barby reported Ganymede as appearing a slight crescent shape through his 4" apo as it was having a nearby moon cast its shadow on it. Buddy being a careful observer noted it but was surprised it was possible to see the moon with an apparent piece missing from it. I'd've thought diffraction would have merely dimmed the moon for Buddy and the 4" but contrast was do super high he saw actual shaped profile. A larger scope would show it sharper more defined and with pointier cusps no doubt but it still surprises me how resolution has gradual borders rather than strict demarcation. I recall he wasn't seeking it on prior suggestion but infact found it but asked why or how it could be .


I wish I had the Peek book though.

Pete


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David Gray
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6359250 - 02/06/14 08:39 AM Attachment (26 downloads)

OK Pete that thread I pondered: I guess you just pushed me to it (I might blame you if it lead-balloons! )

As a taster I put this quote here from “Planets and Satellites” (1961): Kuiper/Middlehurst.

(page 567: Dollfus: Visual and Photographic Studies at the Pic Du Midi) –

“Ganymede has shown whitening at the sunrise limb, covering permanent surface detail; this might be an indication of temporary light deposits on the ground or morning haze.”

Perhaps another “pointless” investigation for those of us who dare to look and report……!

Finally attached is a view more relevant here: a tinted version of what I posted on my Callisto thread: http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6294206/page... (#6297566)

“Further included was a particularly detailed view of Jupiter on Dec. 30 last. When such near perfect conditions arise the standard BAA 64mm x 60mm ellipse-outline is hopelessly too small. So I have on hand some that are 2x larger in the hope of getting that excellent-seeing ‘masterpiece’ I have dreamed of.

I felt good that night and up for it, but had to admit defeat in spite of the almost leisurely way I was seeing fine detail and x720 (monovu) used for much of it. As stump-painting detail is about three times as fast as using a good-pointed pencil especially on all that expanse I thought I had a chance…….out of my depth....! However as Io was in transit (a sharp ‘bite’ in the SEB(N)n) I decided to focus my attention there and work outward; thus what is shown here is a crop from the 5” ellipse where things are most ‘finished/complete’ – hah....!

I have had in mind (been sidetracked a few times tho’) to add the saved colours to this and perhaps put on the Sketching Forum with the satellites also showing the detail I got – even my first ever detail on Europa, albeit a very fugitive shading – what a night.....but I wanted all of Jupiter!”


Dave.


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: David Gray]
      #6360778 - 02/06/14 09:53 PM

Quote:

...for those of us who dare to look and report……!



I raise my glass to those of us who dare to look and report.


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azure1961p
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Re: Some thoughts on a Transit of Io new [Re: Asbytec]
      #6361036 - 02/07/14 12:20 AM

That's a terrific rendering David. In fact its quite riveting.

I don't see defeat in not being able to capture it ALL that high a detail in the seeing provided. Even at half your angular res with my 8" on one of *those* nights I have to focus on a part of Jupiter to do it justice (mind you its been years since I had that grade of seeing for the seasons jupiter is visible in Just dont provide the needed edge to be a 1 Ant. .

Not to side track here but I see you have a ghost if a shading in Europa - the toughest of the bunch!!! That's a fine call!! I'm so used to seeing the garish flyby sat image of it that I wish Id finally see a decent closer-to-reality contrast as shot by Hubble in this difficult target. I know Ganymede looks great with HST but as of yet no such luck with my searches for Europa. Id laugh if it were still a pale snowball!

Going back to your pursuit of the perfect Jupiter under optimum
seeing conditions - it seems like it'd be an impossible undertaking - even with my 8"!! The gestalt of contrasts and details materializing - I couldn't do it. And the times when that did occur I didn't draw at all - I was too stunned. It was like a hunters buck-fever. If have to discipline myself to tunnel vision on a specific area and draw and the real estate but would be none too expansive. In winter though (sighing here) I NEVER have such "problems" arise. A good night is Picketing 6 and bad is 4!!!!! 7 Pickering is reason enough to stay up late and call out of work the next day. Lol - Ive been going to work with out interruption unfortunately!

I promise myself that when *that view* hits again Ill be composed and ready and disciplined . On Saturn and Mars this is possible. With Jupiter - lol -I don't know. Id do my best and try to achieve fidelity in what corner of the planet I focus but - with everything around it bristling with contrast...

Pete


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David Gray
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6361366 - 02/07/14 07:16 AM

Thanks Pete,

Yes you are right with "too stunned"; how often after the event have scolded myself for not making more of it instead of standing there in dumbfounded-enchantment. That is why on that occasion I took myself in hand but to little more avail with regard to the aspired result. But as they say reach for the stars and hit the moon. Well I reached for all of Jupiter and got Io pretty well as to detail... and of course will have to try for the full thing again

Cheers,
Dave.


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Re: Some thoughts on a Transit of Io new [Re: JasonBurry]
      #6382420 - 02/18/14 09:52 AM

Here's a terrific image that shows Ios egg shape compared to Ganymedes round profile quite well.
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=Imaging&am...,,,f57,,,&Words=ganymede&Searchpage=3&Limit=25&Main=6306151&Search=true&where=bodysub&Name=&daterange=1&newerval=2&newertype=m&olderval=&oldertype=&bodyprev=#Post6307475

Pete


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Asbytec
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Re: Some thoughts on a Transit of Io new [Re: azure1961p]
      #6382426 - 02/18/14 09:58 AM

Pete, Io is not as elongated as your post!

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