Kepler's Physical AstronomyFrom Hipparchus and Ptolemy in the ancient world, through Copernicus and Brahe in the sixteenth century, astronomers had used geometrical models to give a kinematic account of the movements of the sun, moon, and planets. Johannes Kepler revolutionized this most ancient of sciences by being the first to understand astronomy as a part of physics. By closely and clearly analyzing the texts of Kepler's great astronomical works, in particular the