My summer astronomy continues. Although a cold front and the remnants of Gustav are making it cloudy for the next few days, last night was pretty good, even from my backyard in the city.
I spent about an hour watching the shadow of a Jovian moon traverse across the face of Jupiter. A moon will look like a star next to Jupiter until it crosses in front of it, whereas you can see the shadow on the face of Jupiter.
According to this Javascript utility on Sky and Telescope's website (with a good article), what I saw was the moon Europa. I couldn't see the moon itself against the disk of Jupiter, but I could see its trailing shadow:
I also used this ancient Java-web-based Jupiter moon calculator from 1997:
