Johannes Kepler made it his life's work to create a heliocentric (sun-centered) model of the solar system which would accurately represent the observed motion in the sky of the Moon and planets over many centuries. Models using many geometric curves and surfaces to define planetary orbits, including one with the orbits of the six known planets fitted inside the five perfect solids of Pythagoras, failed.

Kepler was able to construct a successful model with the Earth the third planet out from the Sun after more than a decade of this trial and error. His model is defined by the three laws named for him. He published the first two laws in 1609 and the last in 1619. They are:

1. The orbits of the planets are ellipses with the Sun at one focus (F₁) of the ellipse.

2. The line joining the Sun and a planet sweeps out equal areas...