I asked a similar question this morning and had some great replies. Have a look at the comments and links on the thread (in beginner's section "was there a moon shadow on jupiter last night?". Great photos and also explanation of what was seen plus some good links referred to.
In the end there was a shadow and a moon visible on the disc
Whenever this situation arises again and you draw what you see at the eyepiece, which is a great thing to do, record the time. That is, record your local time and convert that to UTC Universal time.
To help you do that there is a terrific little application called Als Clock that you can down load from, I think, the resources section of IIS.
Having done this it is then possible to positively identify what ever features you have drawn.
Depending on the time last night you could have seen, Europa's shadow and Ganymede or Ganymede and its shadow.
If you check the solar system images forum you will see images of Jupiter from last night by Stuart and myself with Ganymede and its shadow transiting Jupiter.
Thanks jim for reference. i soon found out that it was ganymede on the surface and europa's shadow by using the jupiter 2 program that i downloaded from that link.
And by using that program today i saw callistos moon shadow about an hour ago.EST time
.
