Kepler's laws

Time line:

Tycho Brahe (1546-1601)
Galileo (1564-1642)
Kepler (1571-1630)
Newton (1643-1727)

Kepler discovered his laws by analyzing the astronomical observations of Tycho Brahe.

Newton subsumed Kepler's laws under his own laws of motion.

Kepler's laws challenged geocentrism and supported the heliocentrism of Copernicus, but did away with Copernicus' circular orbits and epicycles in favour of ellipses.

The laws:

1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.