(1571-1630) German mathematician, astrologer, and astronomer. Born at Weil der Stadt, Wurtemberg; died at Regensburg, Bavaria. Son of a professional soldier, he suffered an attack of smallpox at age 3, which crippled his hands and weakened his eyes. He, therefore, initially planned a career as a minister. He was graduated from the University of Tubingen in 1588, and received a Master's degree in 1591. He taught science at the University of Graz in Austria. As professor of astronomy, he calculated `horoscopes' and carefully studied the Greek writers in a genuine desire to raise astrology to the level of a respectible science. His clients included Emperor Rudolf II and General Albrecht von Wallenstein. He explored the use of astrological methods to probe various Biblical passages. And, he derived the year BC3992 for the date of Creation. He accepted a position at Prague with the aging Tycho Brahe. On Tycho's death, in 1601, Kepler inherited the elder man's valuable collection of careful observations of the apparent motion of the planet Mars. With this precise data, was able to formulate a new theory of planetary motion (so-called `laws'), which eliminated the complex system of Ptolemaic astronomy, with its epicycles and deferents, in favor of simple elliptical orbits. He successfully applied his theory to the motion of the Galilean satellites of Jupiter, but his attempts with the Moon were not so pleasing (the Moon's motion was too complex). Supported by two Holy Roman Emperors, Rudolf II and Matthias, Kepler was able to continue his work (although both rulers were usually late with salary payments). Kepler used the natural logarithm tables, published in 1614, by Napier for his difficult calculations. In 1627, he published his planetary tables (called the Rudolphine Tables, in honor of Rudolf II), dedicating them to the memory of Tycho. This major work was completed in spite of family and financial problems (he had 14 children), wars, and religious upheavals. In 1620, his mother (who was interested in the occult) was arrested as a witch. [She was not tortured, but after prolonged efforts on Kepler's part, she died soon after release.] Kepler corresponded with Galileo, and used one of the latter's telescopes to observe the satellites of Jupiter. He wrote descriptions for an improved telescope (using two convex lenses), and for a parabolic mirror, which was later used in the reflecting telescope of Newton. Kepler's determination of the moments when the planets Mercury and Venus would transit across the Sun's disk led to a new triumph in astronomy; such phenomona had not previously been observed. Not until 1631, after Kepler's death, was the transit of Mercury observed by Gassendi. He wasted much time in his attempt to match planetary motions with musical notes ("music of the spheres") as advocated by the Pythagoreans, and in the use of regular geometric solids to approximate the relative mean heliocentric distances of the planets. He was the first astrologer to formulate a general theory of aspects, both major and minor, and he introduced the quintile aspect. One of Kepler's other books, which contains his "third law", is full of mystism, and was dedicated to King James I of Great Britain. A century after Kepler's death, Catherine II of Russia purchased Kepler's manuscripts, and they are now preserved at the Pulkovo Observatory, Russia.