Kepler, Johannes

(born Dec. 27, 1571, Weil der Stadt, Württemberg—died Nov. 15, 1630, Regensburg) German astronomer. Born into a poor family, he received a scholarship to the University of Tübingen. He received an M.A. in 1594, after which he became a mathematics teacher in Austria. He developed a mystical theory that the cosmos was constructed of the five regular polyhedrons, enclosed in a sphere, with a planet between each pair. He sent his paper on the subject to Tycho Brahe, who invited Kepler to join his research staff. In attempting to understand atmospheric refraction of light, he became the first to explain accurately how light behaves within the eye, how eyeglasses improve vision, and what happens to light in a telescope. In 1609 he published his finding that the orbit of Mars was an ellipse and not the perfect circle hitherto presumed to be the orbit of every celestial body. This fact became the basis of the first of Kepler's three laws of planetary motion. He also determined that planets move faster as they near the Sun (second law), and in 1619 he showed that a simple mathematical formula related the planets' orbital periods to their distance from the Sun (third law). In 1620 he defended his mother from charges of witchcraft, thereby preserving his own reputation as well.

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