This simulation of the 4 Galilean satellites orbiting Jupiter shows how fast the satellites move. Click on the Play button. Each step is 1 hour.
The calculation scheme is given in Jean Meeus: "Astronomical Algorithms", 2nd edition (corrected August 2009), Willmann-Bell Inc. The lower accuracy scheme of the two given in chapter 44 is used. This is accurate enough to show the layout on a given date but not accurate enough to show whether the satellites occult or eclipse each other.
Applet written by Graham Relf - see www.grelf.net