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Kepler

Johannes Kepler (1571–1630) had been destined by his parents for a career as a Lutheran minister. While studying theology at the university at Tübingen (TOO-bing-un), however, he fell under the influence of Michael Mästlin (MEST-lin), Germany’s best-known astronomer, and spent much time pursuing his real interests, mathematics and astronomy. He abandoned theology and became a teacher of mathematics and astronomy at Graz in Austria.

Kepler’s work illustrates well the narrow line that often separated magic and science in the early Scientific Revolution. An avid astrologer, Kepler possessed a keen interest in Hermetic mathematical magic. In a book written in 1596, he elaborated on his theory that the universe was constructed on the basis of geometric figures, such as the pyramid and the cube. Believing that the harmony of the human soul (a divine attribute) was mirrored in the numerical relationships existing between the planets, he focused much of his attention on discovering the “music of the spheres.” Kepler was also a brilliant mathematician and astronomer and, after Brahe’s death, succeeded him as imperial mathematician to Rudolf II. There he gained possession of Brahe’s detailed astronomical data and, using them, arrived at his three laws of planetary motion. These laws may have confirmed Kepler’s interest in the “music of the spheres,” but more important, they confirmed Copernicus’s heliocentric theory while modifying it in some ways. Above all, they drove another nail into the coffin of the Aristotelian-Ptolemaic system.

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On the Revolutions of the Heavenly Spheres

Nicolaus Copernicus began a revolution in astronomy when he argued that the sun and not the earth was at the center of the universe. Expecting controversy and scorn, Copernicus hesitated to publish the work in which he put forth his heliocentric theory. He finally relented, however, and managed to see a copy of it just before he died.

Nicolaus Copernicus, On the Revolutions of the Heavenly Spheres

For a long time, then, I reflected on this confusion in the astronomical traditions concerning the derivation of the motions of the universe’s spheres. I began to be annoyed that the movements of the world machine, created for our sake by the best and most systematic Artisan of all [God], were not understood with greater certainty by the philosophers, who otherwise examined so precisely the most insignificant trifles of this world. For this reason I undertook the task of rereading the works of all the philosophers which I could obtain to learn whether anyone had ever proposed other motions of the universe’s spheres than those expounded by the teachers of astronomy in the schools. And in fact first I found in Cicero that Hicetas supposed the earth to move. Later I also discovered in Plutarch that certain others were of this opinion. I have decided to set his words down here, so that they may be available to everybody:

Some think that the earth remains at rest. But Philolaus the Pythagorean believes that, like the sun and moon, it revolves around the fire in an oblique circle. Heraclides of Pontus and Ecphantus the Pythagorean make the earth move, not in a progressive motion, but like a wheel in a rotation from the west to east about its own center.

Therefore, having obtained the opportunity from these sources, I too began to consider the mobility of the earth. And even though the idea seemed absurd, nevertheless I knew that others before me had been granted the freedom to imagine any circles whatever for the purpose of explaining the heavenly phenomena. Hence I thought that I too would be readily permitted to ascertain whether explanations sounder than those of my predecessors could be found for the revolution of the celestial spheres on the assumption of some motion of the earth.

Having thus assumed the motions which I ascribe to the earth later on in the volume, by long and intense study I finally found that if the motions of the other planets are correlated with the orbiting of the earth, and are