The applet on Page 2 simulates the motion of a planet around the sun (or another fixed star), or the motion of a moon or satellite around a planet.

For detailed information on how to use the applet, go to Applet Help on the applet's Help menu and look at Help and ShowMe. A Lesson accompanying the applet is available there as well.

"Activities" under Related Items suggests investigations to be carried out with the applet on the Galilean velocity transformation relating different inertial reference frames.