Kepler, Johannes (1571–1630)
- German astronomer who used Tycho Brahe’s data to produce the three laws describing the motion of the planets around the Sun, demolishing the ancient view that all celestial motion had to be circular and uniform. He arrived at this solution after numerous false starts, including the idea that the orbits of the planets could be described by shapes within the perfect geometric solids like the sphere and the cube. He finally produced the laws of planetary motion after a lengthy fight with Brahe to get access to his best data on Mars – the inner planet with the most eccentric orbit – which was found to be eight minutes of arc from its theoretical position under the old cosmology. He was also a pioneer of optics and of the calculus, and like many astronomers of his era cast horoscopes, both because he believed in astrology and for money.