Introduction to Astronomy Kepler's New Astronomy Three Models Kepler's Departure Finding "Oppositions" The "Mean" Sun Twelve Observations Ptolemy's "Equant" A "Vicarious Hypothesis" Earth's Motion An "Immaterial Species" Area-Time Principle An Ellipse Conclusion On Proportion Recommended Books

Johannes Kepler (1571-1630) is unique among scientific discoverers in presenting not only his discoveries but also the process by which he arrives at them. Kepler’s 650-page Astronomia Nova ("The New Astronomy") records the astronomer's ten-year long struggle to understand the orbit of Mars (his “warfare with Mars,” as he playfully calls it, for Mars was the Greek god of war). In the pages that follow we outline the scientific problems Kepler confronted as he sought to understand the physical causes of planetary motion. The breadth of Kepler's contribution to science is often not fully recognized: Kepler discovered not only elliptical orbits and the principles of planetary motion but also universal gravitation as well.

His discoveries motivated the development of Calculus.

Readers may wish to review our Beginning Astronomy page before diving into Kepler's Discovery.