During periods of about six months separated by about six years, mutual events occur involving the Galilean satellites occulting and transiting each other, with similar effects from their shadows. The next such period will commence on 2021 JAN 03 and end on 2021 JUN 26. They will be included with my Nightly Events Timetable for Galilean Satellites: https://www.CurtRenz.com/jupiter.html

Photos and descriptions of these events would be welcome additions to this thread.