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Johannes Kepler
Johannes Kepler was the first to apply the new mathematics to understand the laws of celestial motion, adopting a Copernican, heliocentric view of the universe from his earliest days. He focused on the number, size, and relation of the planets, and, after years of calculations and attempts to fill the gaps in his theories, he finally created a model of the universe that satisfied him. While this model was inaccurate, Kepler’s work was not yet done.
In 1609, Kepler published New Astronomy with Commentaries on the Motions of Mars. The work clearly sets forth two of the tenets of modern astronomy: 1) that the planets orbit the sun in ellipses, and 2) that they do not do so uniformly (that is, their orbital speed varies over time). In 1618, Kepler presented the third law of planetary motion, which stated that, as a planet’s distance from the sun increased, so did the time it took to complete its orbit. These observations were all at least somewhat accurate and led to the final discarding of Aristotelian cosmology by the academic world.
Kepler’s Limitations
Kepler's idea of the universe was based on his study of the ancient theorists, which, combined with years of indoctrination, had instilled in him a sense of mysticism. He was convinced that the arrangement of the universe must correspond with some concept of geometric harmony and beauty. Thus, he sought a simple mathematical solution to the problem of mapping the universe, trusting that the laws of nature would provide one. This was a regression in the attitudes of the seventeenth century astronomers, most of who were prepared to accept an irregularly shaped universe, or at least one that did not fit any simple geometric scheme. However, Kepler persisted in his efforts to discover a universe that worked under a unified grand scheme. Though he attempted to map the solar system in this method, he repeatedly failed due to his convictions.
Galileo and the Church
Galileo Galilei was the most well-known and successful scientist of the Scientific Revolution, save Isaac Newton. In 1604, by observing the appearance of a new luminous body in the remote region of space for which no motion of the stars could be detected, he demonstrated that the remote and, according to Aristotelian cosmology, static region of space was not actually static. In 1609, Galileo introduced both the telescope and the microscope. His first observations with the telescope were published in 1610, in a 24-page booklet entitled Messenger of the Heavens.
In 1612, Galileo announced that, through the observation of dark spots on the sun, he had concluded that the sun itself was revolving. This announcement created one of his first conflicts with the Church, which considered these findings contrary to Church doctrine. By 1630, Galileo had completed his magnum opus, Dialogue on the Two Chief Systems of the World, comparing geocentric and heliocentric systems, and finding the heliocentric model far superior. This, too, was in direct opposition to the Church, and led to the prohibition of his book. Galileo himself was found guilty of heresy and forced to sign a recantation of his theories.
Galileo’s Contributions
Galileo, devoid of any adherence to mysticism, posed a sharp contrast to Kepler. More than any other scientist of the era, he introduced the change in thought that broke with the ancients and led to modern science. Perhaps his greatest theoretical contribution was the argument that the laws of physics operated equally everywhere, a conclusion that vastly expanded the possibility for better understanding of astronomy through terrestrial experimentation.
Galileo also developed tools, both mathematical and physical, to explore the universe on all of its levels. The telescope allowed for magnification and better resolution of objects at a great distance, and the microscope allowed scientists to observe the complexity of nature on a smaller scale than ever before. However, there was still much more work to be done in the exploration of the heavens. Galileo had not fully integrated his physics with Kepler's theories on the motions of celestial bodies. That was left to Isaac Newton.
