Kepler's Astronomia Nova

Kepler's Astronomia Nova, published in 1609, marked a major shift in understanding planetary motion. Kepler proposed that planets move around the Sun in elliptical orbits—not perfect circles—and that planets speed up as they approach the Sun. This work was based on detailed observations by Tycho Brahe and introduced the two laws of planetary motion: planets orbit in ellipses with the Sun at one focus, and a line from a planet to the Sun sweeps out equal areas in equal times. These insights fundamentally changed astronomy, emphasizing mathematical modeling over ancient ideas, and laid the groundwork for Newton's law of gravitation.