KEPLER

Kepler (1571-1630) used the observations of Tycho Brahe to show that Mars traveled on an elliptical orbit.

He will propose then the laws that bear his name :

- each planet describes an ellipse where the Sun occupies one of the focus ;
- the areas described by the planet-Sun radius vector is proportional to the time employed to describe them ;
- the semi-major axis a and the revolution period around the Sun T are connected by a³/T²=the same constant for all planets.