Kepler, Johannes

(1571-1630)

   German mathematician and astronomer. His family relocated to the Protestant state of Württemberg while he was still a small child. This principality had developed a strong educational system, and young Kepler benefitted from a scholarship to an excellent Latin grammar school. He then entered the University of Tübingen intending to become a minister, but he studied there with a mathematician who accepted the new heliocentric astronomical system of Copernicus. Kepler had not intended to focus on mathematics, but the university recommended him as a teacher of mathematics in a Protestant seminary in Graz, a predominantly Catholic city. His added duties as district mathematician required him to draw up astrological calendars.

   Kepler's first mathematical publication, Mysterium cosmographicum / Secret of the Universe (1596), suggested that the truth of Copernicus' system of astronomy was confirmed by his conclusion that the orbits of each of the planets in the Copernican system could be inscribed as tangents to one of the five geometrical solids of Euclidean geometry. The book attracted attention, and Kepler was invited to become an assistant to the Danish astronomer Tycho Brahe. Although Brahe opposed Copernicus' heliocentric theory and supported a compromise between it and the old Ptolemaic system, Kepler knew that Brahe had amassed a vast treasure of precise astronomical observations in his observatory and was eager to gain access to these important new data.

   When Brahe left Denmark to become court astronomer to the Emperor Rudolf II, Kepler returned to Graz but found that the Habsburg archduke was increasing pressure on local Protestants to turn Catholic. Hence he rejoined Brahe at Prague, where in 1601, following Brahe's death, he succeeded to the position of imperial mathematician. He continued to fulfill Brahe's official duty of compiling tables of the planetary orbits. By 1605 he had completed work on another major book, Astronomía nova / The New Astronomy, though publication was delayed until 1609. In this book Kepler demonstrated many complex relations among the planetary orbits. Many of these had no particular usefulness but two of them stated what are now known as Kepler's first two laws of planetary motion. In this book for the first time he abandoned his youthful belief that the force that moved the heavens was spiritual and attempted to derive all motions from purely material, physical forces.