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'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). This project unlocked for him the deeper mysteries of the organization and physical dynamics of the Solar System.  Kepler (1571-1630) is relatively unique among scientific discoverers in presenting not only his discoveries but also the history of the process by which he arrived at them. The pages that follow represent a bastasic conceptual introduction to the Astronomia Nova.