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Kepler, Johannes (yōhäˈnəs kĕpˈlər) [key], 1571–1630, German astronomer. From his student days at the Univ. of Tübingen, he was influenced by the Copernican teachings. From 1593 to 1598 he was professor of mathematics at Graz and while there wrote his *Mysterium cosmographicum* (1596). This work opened the way to friendly intercourse with Galileo and Tycho Brahe, and in 1600 Kepler became Tycho's assistant in his observatory near Prague. On Tycho's death (1601) Kepler succeeded him as court mathematician to Holy Roman Emperor Rudolf II. In 1609 he published the results of Tycho's calculations of the orbit of Mars. In this celebrated work were stated the first two of what became known as Kepler's laws. In 1612, becoming mathematician to the states of Upper Austria, he moved to Linz. He wrote an epitome of the astronomy of Copernicus in 1618, and in 1619 *De cometis* and *Harmonice mundi* (in which was announced the third of Kepler's laws). In 1626, Kepler moved to Ulm. After his death his manuscript writings, bought by Catherine II of Russia, were placed in the observatory of Pulkovo.

See biographies by M. Caspar (tr. 1959, repr. 1962) and A. Armitage (1966); A. Beer, ed., *Kepler: Four Hundred Years* (1974).

*The Columbia Electronic Encyclopedia,* 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.