Johannes Kepler

Johannes Kepler was born December 27, 1571. He was a German mathematician, astronomer, astrologer, and a key figure in the seventeenth century. He is best known for his eponymous laws of planetary motion. He believed that God had created the world according to an intelligible plan that through the natural light of reason.

Kepler's first major astronomical work, Mysterium Cosmographicum, was the first published defense of the Copernican system. On July nineteenth 1595 he had an epiphany. He realized that regular polygons bound one inscribed and one circumscribed circle at definite ratios, which, he reasoned, might be the geometrical basis of the universe. After this hypothesis failed he began to look into three-dimensional polyhedral. He realized that regular polygons bourn one inscribed and one circumscribed by spherical orbs; nesting these solids, each encased in a sphere, within one another would produce six layers, corresponding to the six known planetsÐ'--Mercury, Venus, Earth, Mars, Jupiter, and Saturn. By ordering the solids correctlyÐ'--octahedron, icosahedrons, dodecahedron, tetrahedron, cubeÐ'--Kepler found that the spheres could be placed at intervals corresponding (within the accuracy limits of available astronomical observations) to the relative sizes of each planet's path, assuming the planets circle the Sun. Kepler also found a formula relating the size of each planet's orb to the length of its orbital period: from inner to outer planets, the ratio of increase in orbital period is twice the difference in orb radius. However, Kepler later rejected this formula, because it was not precise enough. Later, he rejected this experiment because he couldn't get it precise enough.

As he indicated in the title, Kepler thought he had revealed God's geometrical plan for the universe. Much of Kepler's enthusiasm for the Copernican system stemmed from his theological convictions about the connection between the physical and the spiritual; the universe itself was an image of God, with the Sun corresponding to the Father, the stellar sphere to the Son, and the intervening space between to the Holy Spirit. His first manuscript of Mysterium contained an extensive chapter reconciling heliocentrism with biblical passages that seemed to support geocentrism.]

With the support of his mentor Michael Maestlin, Kepler received permission from the TÐ"јbingen university senate to publish his manuscript, pending removal of the Bible exegesis and the addition of a simpler, more understandable description of the Copernican system as well as Kepler's new ideas. Mysterium was published late in 1596, and Kepler received his copies and began sending them to prominent astronomers and patrons early in 1597; it was not widely read, but it established Kepler's reputation as a highly skilled astronomer. The effusive dedication, to powerful patrons as well as to the men who controlled his position in Graz, also provided a crucial doorway into the patronage system.

Though the details would be modified in light of his later work, Kepler never relinquished the Platonist polyhedral-spherist cosmology of Mysterium Cosmographicum. His subsequent main astronomical works were in some sense only further developments of it, concerned with finding more precise inner and outer dimensions for the spheres by calculating the eccentricities of the planetary orbits within it. In 1621 Kepler published an expanded second edition of Mysterium, half as long again as the first, detailing in footnotes the corrections and improvements he had achieved in the 25 years since its first publication.

Kepler started to court Barbara MÐ"јller, a widow (twice over) with a young daughter, in December 1595. Her father Jobst initially opposed a marriage despite Kepler's nobility; though he had inherited his grandfather's nobility, Kepler's poverty made him an unacceptable match. Jobst relented after Kepler completed work on Mysterium, but the engagement nearly fell apart while Kepler was away tending to the details of publication. After church officials Ð'-- who had helped set up the match Ð'-- pressured the MÐ"јllers to honor their agreement Barbara and Johannes were married on April 27, 1597.

In the first years of their marriage, the Keplers' had two children, both of whom died