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   Copernicanism and the Bible The start of Galileo’s telescopic observations was not the only significant event of the year 1609. In that same year Kepler published his New Astronomy, in which he derived, from the numerous precise observations by Tycho Brahe, an elliptical orbit for Mars with the Sun located at one of the foci. He later extended this result to the orbits of all of the other planets. This is known as Kepler’s first law. He then formulated a second law which described the variation in a planet’s velocity as it orbited the Sun. In later works, the Harmony of the World (1619) and Epitome of Copernican Astronomy (1617–21), he formulated a third law, which relates the orbital period of each planet to its distance from the Sun. By doing away with the dogma of circular orbits Kepler brought substantial improvements to the Copernican system. On the basis of his first two laws, epicycles, deferents, equants, and similar geometric constructions became superfluous and the simplicity of the Copernican system finally became lucidly clear. On the other hand, without the development of a new dynamics it was impossible to grasp the full significance of Kepler’s laws. The result was that most of Kepler’s contemporaries , including Galileo, did not note the importance of Kepler ’s laws, at least until the publication of the Rudolphine Tables (1627). It would take another forty years before Kepler’s laws become widely 33 Fantoli-02_Layout 1 1/16/12 12:48 PM Page 33 known and another twenty before they would be applied to the formulation of a new dynamics in the Mathematical Principles of Natural Philosophy of Isaac Newton. In contrast to the New Astronomy of Kepler, the Starry Messenger of Galileo immediately aroused great interest. The first printing of five hundred copies was sold out within a week. Galileo sent a copy to the Tuscan ambassador to the court of the emperor of the Holy Roman Empire, at Prague, with a request to have it read by the Imperial Mathematician Kepler. In fact, the ambassador informed Galileo on April 19 that Kepler had read the book and was very pleased with it. But because his telescope was imperfect, Kepler confessed, he had not been able to verify Galileo’s observations (Galileo, Opere, 10:318–19). On that same day Kepler himself sent a long letter to Galileo in which at the beginning he lamented the fact that he had not heard from Galileo in a long time and that he had received no comments from him on the New Astronomy. Nevertheless, he said that he was convinced that Galileo’s observations were true and that the conclusions he drew from them were justified. But he was cautious in the way he expressed himself since he had not been able personally to verify the observations (Galileo, Opere, 10:319–40). A little later Kepler published that letter with some modifications as Conversations with Galileo’s Starry Messenger. Although prudent, the position taken by Kepler was clearly favorable to Galileo. But there were astronomers who were hostile, among them the most well-known Italian astronomer of that period, Giovanni Antonio Magini, who taught mathematics at Bologna. On the way to his return from Florence Galileo had stopped on April 24–25 at Magini’s home with the obvious intention of winning the support of this influential professor. Unknown to Galileo was the fact that just before his visit Magini had sent a very negative judgment on the Starry Messenger and on the telescope to the Cologne elector (Galileo, Opere, 10:345). Magini had also written at almost the same time to Kepler asking his opinion about the satellites of Jupiter (10:341). Kepler answered him on May 10 and sent him a copy of his Conversations with Galileo’s Starry Messenger with this pointed comment: Take it and excuse me. We [Kepler and Galileo] are both Copernican . Like attracts like. But I think that, if you read it carefully, you 34 ✦ The Case of Galileo Fantoli-02_Layout 1 1/16/12 12:48 PM Page 34 will note that I have expressed myself cautiously and have reminded Galileo to stick to his own principles. (10:353) But Magini could not agree with Kepler’s discussions. In his reply to Kepler he stated that the attempt by Galileo, during his stopover in Bologna, to show the satellites of Jupiter “to more than twenty educated persons” at his home was a...


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