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Johannes Kepler (December 27, 1571 – November 15, 1630) was a German Lutheran mathematician, astronomer and astrologer, and a key figure in the 17th century astronomical revolution. He is best known for his eponymous laws of planetary motion, codified by later astronomers based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican Astronomy.
Before Kepler, planets' paths were computed by combinations of the circular motions of the celestial orbs. After Kepler, astronomers shifted their attention from orbs to orbits—paths that could be represented mathematically as an ellipse. Kepler's laws also provided one of the foundations for Isaac Newton's theory of universal gravitation.
During his career Kepler was a mathematics teacher at a Graz seminary school, an assistant to Tycho Brahe, the court mathematician to Emperor Rudolf II, a mathematics teacher in Linz, Austria, and an adviser to General Wallenstein. He also did fundamental work in the field of optics and helped to legitimize the telescopic discoveries of his contemporary Galileo Galilei.
Kepler lived in an era when there was no clear distinction between astronomy and astrology, but there was a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of the more prestigious discipline of philosophy). Kepler also incorporated religious arguments and reasoning into his work, motivated by the religious conviction that God had created the world according to an intelligible plan which was accessible through the natural light of reason. Kepler described his new astronomy as "celestial physics," as "an excursion into Aristotle's Metaphysics," and as "a supplement to Aristotle's On the Heavens," transforming the ancient tradition of physical cosmology by treating astronomy as part of a universal mathematical physics.
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