Kepler's laws

Kepler’s Laws of planetary motion is based on his analysis of Tycho Brahe's long and detailed observations of the orbits of the planets.
 * The laws are:

1. The planets orbit the Sun in elliptical orbits, with the Sun as one common focus.

2. The line between a planet and the Sun (the radius vector) sweeps out equal areas in equal periods of time (sometimes called the Law of Equal Areas).

3. The square of a planet's period, T, is directly proportional to the cube of its average distance from the Sun, r: T2 ∝ r3.