You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar

Observing >> Planetary and Solar System Observing Previous   Index   Next   Threaded

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all) Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Some thoughts on a Transit of Io [Re: fred1871]       #5569992 - 12/13/12 09:33 PM Edit   Reply   Quote Quick Reply   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. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5570075 - 12/13/12 10:31 PM Edit   Reply   Quote Quick Reply   The first diffraction ring in ct is cause for a gazzoo. Pete Post Extras:       fred1871 sage Reged: 03/22/09 Loc: Australia Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5570172 - 12/14/12 12:01 AM Edit   Reply   Quote Quick Reply   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. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: fred1871]       #5570226 - 12/14/12 12:56 AM Edit   Reply   Quote Quick Reply   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 Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Some thoughts on a Transit of Io [Re: azure1961p]       #5570275 - 12/14/12 02:59 AM Edit   Reply   Quote Quick Reply   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. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5570398 - 12/14/12 07:18 AM Edit   Reply   Quote Quick Reply   That is a good question. Pete Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: JasonBurry]       #5844954 - 05/07/13 06:08 AM Edit   Reply   Quote Quick Reply   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 Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Some thoughts on a Transit of Io [Re: azure1961p]       #5845640 - 05/07/13 01:38 PM Edit   Reply   Quote Quick Reply   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 Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5846710 - 05/07/13 09:53 PM Edit   Reply   Quote Quick Reply   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 Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Some thoughts on a Transit of Io [Re: azure1961p]       #5846881 - 05/07/13 11:20 PM Edit   Reply   Quote Quick Reply   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. Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5847258 - 05/08/13 07:45 AM Edit   Reply   Quote Quick Reply   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 Post Extras:       JasonBurry sage Reged: 04/27/12 Loc: Cape Spencer, NB, Canada Re: Some thoughts on a Transit of Io [Re: azure1961p]       #5847297 - 05/08/13 08:27 AM Edit   Reply   Quote Quick Reply   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 Post Extras:       Asbytec Guy in a furry hat Reged: 08/08/07 Loc: La Union, PI Re: Some thoughts on a Transit of Io [Re: JasonBurry]       #5848079 - 05/08/13 03:59 PM Edit   Reply   Quote Quick Reply   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 Post Extras:       Classic8 professor emeritus Reged: 04/12/06 Loc: Naperville, IL, USA Re: Some thoughts on a Transit of Io [Re: Asbytec]       #5860424 - 05/14/13 05:05 PM Edit   Reply   Quote Quick Reply   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? Post Extras:       azure1961p Postmaster Reged: 01/17/09 Loc: USA Re: Some thoughts on a Transit of Io [Re: Classic8]       #5861108 - 05/14/13 10:28 PM Edit   Reply   Quote Quick Reply   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 Post Extras:       JasonBurry sage Reged: 04/27/12 Loc: Cape Spencer, NB, Canada Re: Some thoughts on a Transit of Io [Re: Classic8]       #5861618 - 05/15/13 08:17 AM Edit   Reply   Quote Quick Reply   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 Post Extras:       Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all)

Previous   Index   Next   Threaded

Extra information 2 registered and 2 anonymous users are browsing this forum. Moderator:  RLTYS  Print Thread Forum Permissions       You cannot start new topics       You cannot reply to topics       HTML is disabled       UBBCode is enabled Thread views: 4141 Jump to *Announcements and News* -----   Cloudy Nights Announcements   Discussion of CN Articles, Reviews, and Reports   Celestial Events*General Astronomy* -----   Beginners Forum   General Observing and Astronomy   Outreach   Light Pollution*Equipment Discussions* -----   ATM, Optics and DIY Forum   Binoculars   Binoviewers   Cats & Casses   Classic Telescopes   Equipment   Eyepieces   Mounts   Observatories   Reflectors   Refractors    Video and Electronically Assisted Astronomy*Astrophotography and Sketching* -----   Beginning and Intermediate Imaging   Film Astrophotography   DSLR & Digital Camera Astro Imaging & Processing   CCD Imaging & Processing   Solar System Imaging & Processing   Sketching   Astro Imaging/Sketching Contest *Observing* -----   NEO   Planetary and Solar System Observing   Lunar Observing   Deep Sky Observing   Double Star Observing   Solar   Variable Star Observing and Radio Astronomy*Telescope Specific Forums* -----   Celestron NexStar    NexStar GPS / CPC Telescopes   Questar Forum   Meade ACF/RCX / LX / GPS    Meade ETX*Speciality Forums* -----   Arizona Science and Astronomy Expo   NEAF (Northeast Astronomy Forum) and NEAIC (Northeast Astro Imaging Conference)   AstroArt   Astronomy Clubs and Star Parties   Astronomy Software & Computers   AstroWebsites   Science! Astronomy & Space Exploration, and Others   Space Rocks   Stellar Media*Swap and Shop* -----   Shop and Swap Audio Components*CN Feedback and Vendor Announcements* -----   Vendor and Group Announcements*International Year of Astronomy 2009 - Forums are now closed.* -----   IYA Archive Info

CN Forums Home