This photograph shows the planets Jupiter and Venus and also the four Galilean moons of Jupiter. In both the solar system and the Jupiter system, the mathematical relationship between the objects' orbital radius and period is the same: the square of the period is proportional to the cube of the radius. -- Kepler's third law expressed this relationship for planets in the solar system (see The Laws of Planetary Motion). -- Newton explained and generalized it (see Gravity, Newton's laws, and the orbits of planets from the University of New South Wales).
Image:
image credit: Mark S. Deprest, University Lowbrow Astronomer, Ann Arbor, MI; image source; larger image
