Topics: Astronomy

Kepler’s third law of planetary motion tells us that the square of a planet’s orbital period is proportional to the cube of the length of the semi-major axis of its orbit.

Mathematically, given:

  • the time required for a given planet to make one orbit around the Sun
  • the length of the major axis of its elliptical orbit

Kepler’s third law tells us that , for some constant . That is, is proportional to .