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azure1961p
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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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Asbytec
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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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JasonBurry
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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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Asbytec
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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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JasonBurry
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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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Eddgie
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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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Asbytec
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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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JasonBurry
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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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Asbytec
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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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Eddgie
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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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Eddgie
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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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azure1961p
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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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Asbytec
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Re: Some thoughts on a Transit of Io [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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JasonBurry
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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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JasonBurry
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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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Asbytec
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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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Asbytec
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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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JasonBurry
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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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