Kepler, the Astronomer

Johannes Kepler gave the Laws of Planetary Motion to the Western world.

His basic postulates are

1) The orbit of a planet is an ellipse, with the Sun as the focus of that ellipse

2) Planets move faster at perihelion and slowest at Aphelion

3) p1^2/p2^2 = a1^3 / a2^ 3, where p = period of revolution of the planet and a its semi major axis.