# Collier's New Encyclopedia (1921)/Kepler, Johann

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Edition of 1921; disclaimer. |

**KEPLER**, or **KEPPLER, JOHANN**, a German astronomer; born in Weil der Stadt, Wiirttemberg, Dec. 27, 1571. He was left to his own resources when a mere child, his education depending on his admission into the convent of Maulbronn. He afterward studied at the University of Tübingen, applying himself chiefly to mathematics and astronomy. In 1593 he was appointed Professor of Mathematics at Gratz, and about 1596 began a correspondence with Tycho Brahé, went to Prague, where he lived for 11 years in great poverty. He then obtained a mathematical appointment at Linz, and 15 years afterward was removed to the University of Rostock. In his “Mystery” (1596), he proclaims that five kinds of regular polyhedral bodies govern the five planetary orbits. At length convinced that this theory was only an error, after 22 years of patient study he was able at last to announce in his “Harmonies of the World” (1619) that the “square of a planet's periodic time is proportional to the cube of its mean distance from the sun.&lrquo; This rule is known as Kepler's Third Law. Finding the theory of epicycles unable to bear the strain of Tycho Brahe's accurate observations, especially in the case of the planet Mars, he endeavored to find a law for the planet's movements which would be simple and satisfactory. After enormous labor, and by a process of trial and error, he found that (1) the planet's orbit was an ellipse, of which the sun is one focus, and (2) that, as the planet describes its orbit, its radius vector traverses equal areas in equal times. These rules (published in 1609 in his work on “The Motions of Mars”) are known as Kepler's First and Second Laws respectively. These laws formed the ground-work of Newton's discoveries, and are the starting-point of modern astronomy. Besides, we owe to Kepler many discoveries in optics, general physics, and geometry. He died in Ratisbon, Nov. 15, 1630.