There are some great mutual satellite events between Jupiter’s moons this month. On 6 December between 22:11 UT and 22:19 UT, Ganymede almost totally occults Io. On 12 December, it’s Europa’s turn to pass across Io. Although this isn’t such a complete occultation, both objects will have a similar apparent size. This event occurs between 23:09 UT and 00:21 UT on the 13th. A repeat meeting on 13 December almost results in a complete transit of Europa across Io’s disc. This occurs between 01:15 UT and 02:24 UT.
Ganymede finally manages to totally occult Io on 14 December between 21:00 UT and 21:55 UT. Callisto’s shadow passes across the disc of Io on 21 December: the whole event starts at 03:13 UT and concludes at 03:32 UT, mid-eclipse being at 03:22 UT. Europa’s shadow eclipses Ganymede on 24 December with mid-eclipse at 06:34 UT, the entire event lasting from 06:24 UT to 06:45 UT.
Finally, there’s a decent partial occultation of Io by Europa on 30 December between 21:38 UT and 21:49 UT. It’s great fun observing these events, especially as they happen pretty quickly. Small telescopes will show the moon dots closing in on one another during an occultation, while an eclipse may result in the eclipsed moon dimming. Large telescopes under steady skies may actually be able to show the discs interacting.