Kepler's New Astronomy

This year (2009) is the 400th anniversary of the publication of Johannes Kepler's book New Astronomy (Astronomia Nova) announcing the discovery of the elliptical orbit of Mars to the world. The discovery of the elliptical orbit of Mars and the mathematical rule of motion for Mars on its elliptical orbit by Johannes Kepler in 1605 is one of the most important advances in astronomy, physics, and science. This discovery transformed the unproven heliocentric theory of Copernicus into a rigorous predictive theory that outperformed the traditional geocentric theory of Claudius Ptolemy and his successors. The discovery paved the way for Newton's theory of gravitation. It remains one of a small number of cases where a simple mathematical rule for seemingly complex and confusing data has been found. In many respects, the discovery of the elliptical orbit of Mars and other planets is more important than the better known work of Kepler's contemporary Galileo. In honor of Kepler, NASA has named its recent mission to look for extra-solar planets, especially possible other Earths that might support life or even intelligence, the Kepler mission.