Some thoughts on a Transit of Io
Posted 04 December 2012 - 11:12 PM
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.
Posted 05 December 2012 - 12:12 AM
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.
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.
Posted 05 December 2012 - 01:58 AM
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.
Posted 05 December 2012 - 04:08 AM
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.
Posted 05 December 2012 - 07:22 AM
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.
Posted 05 December 2012 - 08:52 AM
Posted 05 December 2012 - 09:36 AM
Posted 05 December 2012 - 01:04 PM
Posted 05 December 2012 - 07:03 PM
Posted 06 December 2012 - 07:28 AM
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.
"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. Other astronomers between 1850 and 1895 noted Io's elliptical shape. 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. 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. 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. 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.
Posted 06 December 2012 - 07:39 AM
Posted 06 December 2012 - 08:08 AM
The reference for Bernard cited, " 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, " 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.
Posted 06 December 2012 - 08:59 AM
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.
Oh, heck yea it was!
That was some interesting reading... Barnard's sketch in the article is illuminating, too.
Posted 06 December 2012 - 09:30 AM
Posted 06 December 2012 - 10:57 AM
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!
Posted 06 December 2012 - 11:47 AM
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.
Posted 06 December 2012 - 12:17 PM
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.
Posted 06 December 2012 - 12:55 PM
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.
Posted 06 December 2012 - 01:28 PM
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.
Posted 06 December 2012 - 01:58 PM
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?
Posted 06 December 2012 - 10:54 PM
Posted 06 December 2012 - 10:56 PM
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.
Posted 07 December 2012 - 07:12 AM
Geepers Eddgie, I've always appreciated your input.
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.
Posted 07 December 2012 - 07:38 AM
It's a good likeness to what I observed, allowing for my crude simulation.