Johannes Kepler Reference

Johannes Kepler

(History of the World: The 17th and 18th Centuries)

Article abstract: Through the application of his exceptional intellect, faith, and tenacity, Kepler created the science of modern astronomy and provided the solid foundation upon which Isaac Newton built his laws of universal gravitation.

Early Life

Johannes Kepler was born prematurely on the afternoon of December 27, 1571, at Weil, Swabia, the first child of Heinrich and Katharine Kepler. His childhood was exceptionally difficult. He was a small, sickly child with thin limbs and a large, pasty face surrounded by dark hair. It is one of the ironies of history that the child who would one day revolutionize astronomy had poor eyesight. His mother was a small, quarrelsome woman with a nasty disposition; his father appears to have had no established trade and, in 1574, simply left the family to fight for the Catholic Duke of Alva in the Netherlands. His mother followed a year later, leaving Kepler in the care of his grandparents, who treated him badly. In 1576, his parents returned, but this provided only a dubious improvement in his family life.

Under such circumstances, it is not surprising that Kepler’s self-image as a child was terrible; he described himself once as a “mangy dog.” Possibly in response to the instability in his life, Kepler developed a pronounced religious disposition at a young age. Indeed, of all his childhood memories only two stood out as pleasant. When he was six, Kepler’s mother took him to a hill to see a comet, and at age nine his parents took him outside to observe an eclipse of the moon. The seeds were planted that would influence the direction of his life.

Yet it was obvious even to his parents that Kepler was a bright child, and school provided a way for him to divert himself from the suffering of family life while building his self-assurance and developing his intellect. Kepler was fortunate that the Lutheran Dukes of Württemberg provided generous educational scholarships for the intelligent sons of poor parents.

Kepler began his schooling at age seven at the Latin school in Leonberg. He completed the curriculum at age twelve, and his intellect, poor health, and pious nature preordained him to a clerical career. After passing a competitive exam on October 16, 1584, Kepler continued his studies at the higher seminary at Maulbronn. On September 17, 1589, he entered the University of Tübingen, where he was particularly influenced by his professor of astronomy, Michael Mästlin. Mästlin was unique in that he believed that Nicolaus Copernicus’ heliocentric theory was essentially true. Influenced by this exceptional teacher, Kepler accepted the Copernican view of the universe—an act that would have a profound impact on his life and the future of scientific thought.

At the age of twenty, Kepler was matriculated at the Tübingen Theological School. His career path seemed assured, but circumstances fatefully intervened. In 1593, the mathematician of the Lutheran high school of Graz died, and the school requested Tübingen to recommend a replacement. Kepler was nominated and agreed to accept the position.

His job was to teach mathematics and to publish the annual calendar of astrological forecasts. Kepler was lucky with his first calendar, correctly predicting a cold spell and a Turkish invasion. Kepler would be involved with astrology all of his professional life, but he did it primarily to supplement his income. Still, while he considered popular astrological forecasts a “dreadful” superstition, Kepler believed that astrology could become an exact empirical science, and with that aim in mind, he would write several treatises on the subject.

Kepler was a terrible teacher. He was often unintelligible, launching into obscure digressions whenever a thought occurred to him. Yet it was during one of these lectures that the event happened that set Kepler on the path that would ultimately lead him to reinterpret the prevailing view of the universe.

Life’s Work

Kepler found his first year at Graz very trying. To escape its frustrations, he turned to the astronomical studies he had experimented with at Tübingen. The more he contemplated the Copernican system, the more he became convinced of its truth, but he was also aware that it was not the final, definitive explanation of the operation of the universe. Already in 1595, Kepler was beginning to ask the questions that would determine that course of his scientific inquiry. Why are there only six planets? What determines their distances from the sun? Why do the planets move more slowly the farther away they are from the sun? These and other queries had been coursing through his mind, when on July 19, 1595, as Kepler was teaching, an incredible thought struck him. On the blackboard, he had drawn a figure showing an outer circle circumscribing a triangle, which enclosed an inner circle. As Kepler looked at the two circles, he was suddenly dumbfounded by the realization that the ratios of the two circles were the same as those of the orbits of Saturn and Jupiter. Could it be that there were only six planets because planetary orbits were related to the five regular solids—the tetrahedron, cube, octahedron, dodecahedron, and icosahedron—of Euclid’s geometry?

This revelation was the basis of Kepler’s first major work, in 1596, Prodromus dissertationum mathematicarum continens mysterium cosmographicum (cosmographic mystery). His thesis was that one of the five regular solids fit between each of the invisible spheres that carried the six planets. The key insight of this book, however, revolved around his search for a mathematical relationship between a planet’s distance from the sun and the time necessary for it to complete its orbit. Kepler concluded that there must be a force emanating from the sun that swept the planets around their orbits. The outer planets moved more slowly because this force diminished in a ratio to distance just as light did. Here is found the first hint of celestial mechanics, the joining of physics and astronomy, that would lead to the laws of planetary motion.

Kepler sent copies of the work to a number of scientists in Europe, including Tycho Brahe, who had spent several years making painstakingly accurate observations of planetary orbits and who would shortly become the Imperial Mathematician of the Holy Roman Empire. While he did not agree with the Copernican underpinning of Kepler’s work, Brahe was impressed by Kepler’s knowledge of mathematics and astronomy, and he invited Kepler to join his staff in the observatory at Benatek, just outside Prague. Kepler was flattered by the invitation, but he had just been married and was too poor to afford the trip. The deteriorating religious situation in Graz, in which Protestants were being forced either to convert to Catholicism or emigrate, compelled Kepler to make a decision. In 1600, Kepler joined Brahe in Prague, where he would remain until 1612....

(The entire section is 2853 words.)