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David Gray
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Reged: 08/06/12

Loc: Co. Durham UK
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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azure1961p
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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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Asbytec
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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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azure1961p
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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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David Gray
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Reged: 08/06/12

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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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azure1961p
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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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David Gray
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Reged: 08/06/12

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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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David Gray
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Reged: 08/06/12

Loc: Co. Durham UK
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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Reged: 08/06/12

Loc: Co. Durham UK
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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azure1961p
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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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