The mass of Jupiter is found by determining the orbital period of one of its satellites, and the distance of the satellite from the planet. The mass of the Sun is found by using the orbital period of the Earth and its distance from the Sun. The period and distance are related to the mass by the simple formula:
2
4 pi G Mass
---------------- = -------------
2 3
Period Distance
where G is the constant of gravity, and pi = 3.14159. This is just Kepler's
Third Law.