The basic force holding the Universe together is gravity. Gravity keeps the Moon orbiting the Earth, the Earth orbiting the Sun, and even the Sun orbiting the center of our galaxy. We can use the laws of gravity -- particularly Kepler's Third Law -- to figure out the mass of a planet from the motions of its moons.

Using this applet, you will "observe" the motions of Jupiter's four biggest moons, and use your observations with Kepler's Third Law to derive Jupiter's mass.

Credits:
    - Scientific Development: Chris Mihos (CWRU)
    - Java Programming: Bob Vawter
    - Web Design: Cameron McBride, Chris Mihos