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I always enjoy watching Jupiter shadow transits around the time of oppposition of the giant planet. In the course of the last week, the shadows cast by Jupiters moons have switched from the preceeding to me following side of the transiting satellites. I had a good view of an Io transit a few days before Jupiter's opposition last Tuesday night, October 19, in my 7 inch Starmaster Dob. Io's shadow, closely followed by Io itself were positioned near Jupiters GRS in the Southern equatorial belt. The shadow and satellite looked almost due east/west of each other, and although not touching, made a striking duet that was great fun to watch just ahead of the GRS.
There were a dearth of good transits for the rest of the week, so I decided to stay up for the first good Io transit on the other side of opposition this morning. Around midnight there was a great view of a clear red spot in Jupiter's NEB, (the same one discussed in recent SHALLOW SKY postings?). The spot looked like it transited Jupiters meridian around 12:45 am PST.
I left the scope outside and came out again about 3 am to find clouds threatening the view of the Io transit that was just scheduled to begin. I carried the scope to a nearby dark hill anyway, and found I could still make out lots of detail on Jupiter through the thin clouds. Io hit Jupiter's limb on schedule about 3:07. I tried to estimate the time when the shadow was first visible, but the fog was at its worst for the next ten minutes or so. I'm glad I stuck with it though, because by 3:20 am skies were much better, and most of the fog or clouds had passed by 3:30. Both Io and its shadow were obvious against the southern equatorial belt,with Io itself positioned slightly to the SW of its shadow. The planet and the shadow appeared to be touching, with maybe a tiny, tiny bite out of the shadow at the point of contact, but certainly no striking crescent to the shadow.
At moments of good seeing I could also see a white spot between the NEB and the moon/shadow, and a small, thin, short, ruddy elongated patch located in Jupiters southern hemisphere below the SEB. This made a nice line up oriented N/S across the face of the planet: NEB, white spot, moon/shadow in an embrace on the SEB, and southern ruddy spot beneath that.
Saturn was better positioned for viewing than Jupiter by that time in the morning, and looked great. The crepe ring was more obvious than any time I have seen it in the last month or so, and clearly wrapped all the way around the planet. I switched back and forth between Jupiter, Saturn, and some old favorite double stars in Orion for awhile, and then packed it in when another big section of clouds rolled in a little after 4am.
The temperatures were in the mid-40s early this morning, and dew was obvious on the finder and outer telescope tube by the end of the session. The combination of viewing conditions and the Galilean satellite's shadows hopping around to the following side gave a real "turn of the seasons" feeling to the observing. I'm glad I stayed up but I hope next years transits around opposition time are at more convenient times.