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    From the Polemics on the Comets to the Dialogue Upon his return to Florence, Galileo did not allow himself to be discouraged . He was certainly well aware of the necessity to keep an attitude of prudent silence on Copernicanism, bounded as he was by the admonition received from Bellarmine and that much more severe from Segizzi. At the same time, optimist by temperament as he was, he must have undoubtedly hoped that, with the lapse of time and with the possibility of finding convincing proofs in favor of the Copernican system , the Church’s attitude could be changed. Making use of the peace and the free time that was once more his, after the years of frantic polemical activity, he returned to his longstanding studies on motion by reorganizing and selecting the materials from his time at Padua. And he dedicated himself also to astronomical observations. But it was a slow undertaking, broken up by periods of sickness, which pushed him to move to the villa of Bellosguardo on the hills surrounding Florence. Despite his good intentions, Galileo’s silence was not to last long. Towards the end of the year 1618 three comets appeared over a short period of time. The third and largest one, in particular, did not fail to 121 Fantoli-05_Layout 1 1/16/12 12:47 PM Page 121 arouse the deep impression that always accompanied the appearance of those heavenly phenomena, interpreted as a forewarning of cataclysms and of wars. In fact, the appearance of these comets coincided with the beginning of the long war that subsequently became known in history as the Thirty Years War, a fact that seemed to confirm such popular beliefs. As usual, extremely heated discussions arose among astronomers and natural philosophers. According to the Aristotelian explanation, adopted by most of the latter, the comets were terrestrial exhalations that, as they rose to the highest zone of the sphere of fire, became heated by the friction caused by the movement of the sphere of the Moon, immediately above it. And they were made to rotate in a circle by effect of the same circular motion of the latter. Their disappearance coincided with the total extinction of their combustible material. Others, and especially the astronomers, subscribed instead more or less faithfully to the opinion of Tycho Brahe. According to it, the comets were located quite a distance beyond the Moon and moved around the Sun in an orbit which was probably not circular but oval, close to the orbit of Venus. And that explained their varying distance from the Earth. According to Brahe, comets were a kind of transient celestial phenomenon, as were the novae, localized, not in the sphere of the “fixed stars” as the latter were, but in that of the planets. Galileo was prevented from observing these comets because of a sickness that forced him to stay in bed during the entire period that they remained visible (see Galileo, Opere, 6:225). On the other hand, he was persuaded (and remained so until the very end of his life) that the phenomenon of the comets was difficult to understand, and thus he preferred to remain silent. A public conference on the comets was held at the Roman College by Father Orazio Grassi (1583–1654), who, at that time, held the chair of mathematics in the place of Grienberger. That conference was published in the following year with the title An Astronomical Discussion of the Three Comets of 1618, but without Grassi’s name, for reasons of prudence . Grassi, in fact, defended an explanation of the phenomenon that could have stirred up polemics with the Aristotelians: he affirmed that the comets were far beyond the Moon, and presumably between the lat122 ✦ The Case of Galileo Fantoli-05_Layout 1 1/16/12 12:47 PM Page 122 ter and the Sun. In that way, he sided with Brahe and against Aristotle. Concerning the center of the comet’s orbit, however, he seemed to consider it to coincide with the Earth and not the Sun, in accordance, in this instance, with Aristotle. Galileo received in advance the news of the printing of the Astronomical Discussion, at the beginning of March 1619, from one of his Roman correspondents, Rinuccini, who wrote to him: The Jesuits presented publicly a Problem [on the distance of the comet] which has been printed and they hold firmly that it is in the sky [that is, beyond the Moon], and some others than the...

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Additional Information

ISBN
9780268158583
Related ISBN
9780268028916
MARC Record
OCLC
785782433
Pages
280
Launched on MUSE
2012-11-02
Language
English
Open Access
No
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