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Starpoke
super member
Reged: 11/14/07
Posts: 146
Loc: Western Montana
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This seems so far out I am reluctant to post it but I am very perplexed by an observation I cannot understand on the evening of Aug 29 from 10 to llpm Local Mountain daylight time from my front yard in Western Montana. I had been observing Jupiter with my 94mm f7 Brandon and a Meade 6.7 UWA. Because of its low altitude I coudn't use higher power but moments of steady seeing hinted at structure in the SEB. Only one moon was visible when I began. At about 10:00 or son a tiny bright point appeared at about the 5 O'clock position on the right side of the disk. (I was using a diagonal so E - W was reversed) It continued to move to the right and when it had reached a distance of about 1/2 disk diamater, it DISAPPEARED! Shortly thereafter another tiny point appeared on the other side of the disk at about the 10:00 possition and started to separate. This was about 11:00pm. I watched a lille longer then needed to retire but before quiting I looked in vain for anything in the area of the missing moon or what-ever-it-was. Can anyone give me a rational explanation of what I saw?
Clear Skies and Open Minds to you all
Glenn
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152nn f9 Starfire Apo on Schaefer AT-4 Mount
94mm f7 Bandon Apo on ASGT (or Polaris when AGST is on the fritz.)
eyepieces, books, some old scopes and mounts - ect.
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Special Ed
Post Laureate
Reged: 05/18/03
Posts: 3543
Loc: Greenbrier Co., WV 38N, 80W
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Starpoke,
You've made an excellent observation of the Galilean moons interacting with Jupiter. At the time you began observing, only Europa was visible--Callisto and Ganymede were behind (occulted by) Jupiter and Io was transiting in front of the Jovian disk. If the seeing had been better, you probably would have noticed the tiny black dot of Io's shadow.
Ganymede reappeared from behind Jupiter at the 5 o'clock position you referred to and not long after that was eclipsed by Jupiter's shadow. Io completed its transit and reappeared at 0500 UT (11:00PM MDT).
You can replay all these events and anticipate future ones by using this handy applet from Sky & Telescope.
Congratulations on this observation. 
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Michael Rosolina
8" f/10 Orange Tube SCT
4.25" f/4.2 Astroscan Reflector
SVP 3.6" f/13.6 CA Reflector
40mm PST f/10
APM Germany HD 15x70 binoculars
Canon 12x36 IS II binoculars
Mark I Eyeball
My CN Gallery
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molniyabeer
Carpal Tunnel
Reged: 01/08/05
Posts: 2062
Loc: Central Coast, California
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Starpoke,
That is a nice report and you got to experience some nifty events. Jupiter is a great object for night-to-night and even hour-to-hour observations. Transits, occultation, eclipse, shadows, the red spot, clouds bands... All sorts of cool stuff that you can watch change in real time.
Clear skies.
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Steve
16" Meade LightBridge (Beowulf)
10" Hardin DSH, StarMax 127mm Mak, PST H-a
Oberwerk 11 x 70 binocs, Tasco 10 x 50 binocs
Santa Maria Clear Sky Clock
Figueroa Mt Clear Sky Clock
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 Centaur
Pooh-Bah
Reged: 07/12/04
Posts: 1123
Loc: Chicago
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Nice observation report, Glenn. The “weird” event was actually a rather common eclipse of a Galilean satellite moving into Jupiter’s shadow. Ganymede (#3) had already emerged from occultation behind Jupiter when your observations began. I calculate that Ganymede began to be partially eclipsed by Jupiter’s shadow at 22:32:51 MDT and was totally eclipsed by 22:41:43 MDT. Io (#1) began finishing a transit at 22:56:59 MDT and moved completely off of Jupiter’s disk at 23:00:35 MDT. Callisto (#4) would have been occulted behind Jupiter during the entire time of your observations. Europa (#2) would have been visible to the west of Jupiter while you were observing. Io's shadow was transiting Jupiter throughout your observation time.
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For astronomical graphics, including
monthly wallpaper calendar, visit:
www.CurtRenz.com/astronomical.html
Curt Renz - "Centaur"
Edited by Centaur (08/31/08 05:10 PM)
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Starpoke
super member
Reged: 11/14/07
Posts: 146
Loc: Western Montana
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Thans Michael and Steve. I had briefly considered that the missing moon had been eclipsed by Jupiter's shadow but I misinterpreted the meaning of the nearby position in Capricornis of Earth's Umbra as shown in Cartes du Ciel as meaning that the shadow of Jupiter would be behind the planet and not so far off to the side. Given the considerable orbital distances of the moons, it makes perfect sense that the satellite would appear and then "go dark." Thank you for setting my mind at ease and reminding me to check stuff out instead of just gawking. I have bookmarked the Sky and Telescope applet for future reference. I really need to learn to use names for stuff I see.
Clear Skies
Glenn
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152nn f9 Starfire Apo on Schaefer AT-4 Mount
94mm f7 Bandon Apo on ASGT (or Polaris when AGST is on the fritz.)
eyepieces, books, some old scopes and mounts - ect.
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Centaur
Pooh-Bah
Reged: 07/12/04
Posts: 1123
Loc: Chicago
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Glenn, perhaps you did not notice my information regarding the eclipse of Ganymede by Jupiter’s shadow. How well does it match your observations?
Below is a graphic I’ve created to illustrate the situation on 2008 AUG 29 at 23:00 MDT.
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For astronomical graphics, including
monthly wallpaper calendar, visit:
www.CurtRenz.com/astronomical.html
Curt Renz - "Centaur"
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canopus56
sage
Reged: 05/01/05
Posts: 298
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In thread "Planetary plays 8-13 to 8-23", Ziggy943 in reply 2592718 - 08/20/08 10:54 AM:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2593324/
- Ziggy graphs out all the many Jovian events for that pretty crowded night in an Excel spreadsheet:
http://www.cloudynights.com/ubbthreads/attachments/2592718-Jupiter%208-29-2008.xls
The little planet appearing at the 10 o'clock position just after 11pm was Io. The planet disappearing at the 5 o'clock position just before 11pm was Ganymede. This was an unusually eventful night for Jupiter satellite phenomenae with an eclipse disappear, a planet and planet shadow transit all within a few hours.
You can determine when these events will occur by reference to the RASC Observer's Handbook Annual. In addition to the Sky and Telescope applet referenced upthread, there is also an online tabular source at the Institut de Mécanique Céleste:
http://www.imcce.fr/page.php?nav=en/ephemerides/phenomenes/ephesat/predictions/Jupiter/phenJup.php
There was also a Great Red Spot transit at 10:47pm that night. You can pick up the GRS transit times using another Sky and Telescope calculator:
http://www.skyandtelescope.com/observing/objects/planets/Transit_Times_of_Jupiters_Red_Spot.html
Good eyes.
- Kurt
See also my eclipse disappear report for 8/29 in thread "Obs rep Ganymede EcD 082908 next Io EcR 090608"
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Starpoke
super member
Reged: 11/14/07
Posts: 146
Loc: Western Montana
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I failed to notice the gradual dimming of Ganymede because I was concentrating on seeing some flashes of detail in the equatorial belts. Sigh, the GRS went right "under my nose" so to speak and I didn't even glimpse it. The 98 power I was using was actually probably more than the seeing would support but I was hoping for one of those moments of clarity. When I began about 10:00 only one moon was visible. I didn't time the appearance or disappearance of Ganymede because, as I said, I was just gawking but the your calculations seem to be right on the money. I feel lucky to have seen such an unusual concentration of satellite events in the short time I had for viewing.
Actually my vision is not very good, but I do see more now than when I starting observing. Would a web cam show me more than I am seeing? I have been looking on Ebay at auctions for Phillips spc 700 and 900 webcams. My computers only have USB 1 and I don't know if they can take that much data at once.
Cheers
Glenn
Clear Skies
Glenn
--------------------
152nn f9 Starfire Apo on Schaefer AT-4 Mount
94mm f7 Bandon Apo on ASGT (or Polaris when AGST is on the fritz.)
eyepieces, books, some old scopes and mounts - ect.
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Special Ed
Post Laureate
Reged: 05/18/03
Posts: 3543
Loc: Greenbrier Co., WV 38N, 80W
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Hey Centaur--great graphic! The spaceman's eyeview hovering above the Jovian north pole makes the geometry of this event very clear and easy to grasp (can you tell that I'm back in the classroom?  )
It might be useful to remind folks that from our point of view here on Terra, shadows precede the outer planets and their satellites before opposition and follow them after opposition. This Jupiter observation, which I made about a month before opposition, illustrates this phenomenon with Callisto's shadow transiting 5 hours before Callisto itself appeared.
@ Starpoke, don't feel bad about gawking--you had plenty going on and took in most of it. The biggest limiting factor for you is probably Jupiter's low altitude from your latitude, even at culmination. You might try your bigger scope which would give you a little better resolution at a little higher magnification if supported by seeing conditions. The other factor within your control is to gain more experience by just logging more hours observing Jupiter and maybe sketching what you see. Sol Robbins, a very experienced and skilled observer, has done some amazing observations with his 3" TMB refractor. From the observation you posted, you're off to a good start in any event. 
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Michael Rosolina
8" f/10 Orange Tube SCT
4.25" f/4.2 Astroscan Reflector
SVP 3.6" f/13.6 CA Reflector
40mm PST f/10
APM Germany HD 15x70 binoculars
Canon 12x36 IS II binoculars
Mark I Eyeball
My CN Gallery
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jmcdonald
Carpal Tunnel
Reged: 06/01/05
Posts: 1503
Loc: Tucson, AZ
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Very interesting observation. That particular sequence of events never occurred to me and I would've been confused too. I wonder if Galileo ever saw the same set of events and what he thought of them?
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Jerel
Discovery 12.5" modified truss DOB
Orion 100mm f/6 achromat
Garret 15x70 LW Binoculars
22-T4,13-T6
IDA Membership
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canopus56
sage
Reged: 05/01/05
Posts: 298
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Starpoke wrote: "as I said, I was just gawking"
Michael wrote: "Starpoke, don't feel bad about gawking--you had plenty going on and took in most of it."
Ditto. Gawking is the purest form of "observing". I do it all the time. - Kurt
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