Johannes Kepler
An astronomer and mathematician who replaced the circles of ancient astronomy with the ellipse: a planet travels around the Sun on a stretched curve with the Sun at one focus. The three laws that bear his name turned celestial mechanics from description into calculation and later underpinned Newton's gravitation. Kepler served as imperial mathematician in Prague, worked through Tycho Brahe's observations, wrote the New Astronomy and the Harmony of the World, and computed the Rudolphine Tables. He practised astrology all his life and earned by it, yet judged it with reservations and rejected much that his contemporaries accepted.
Born in Weil der Stadt on 27 December 1571 at 14:30 local mean time: the German lands had no single time zone then, and the hour is referred to the city's longitude. The hour is known more precisely than for anyone else of his century — Kepler cast his own horoscope and recorded his birth time, returning to recompute it later.