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Galileo: Telescopes
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As a professor of astronomy at University of Pisa, Galileo was required to teach the accepted theory of his time that the sun and all the planets revolved around the Earth. Later at University of Padua he was exposed to a new theory, proposed by Nicolaus Copernicus, that the Earth and all the other planets revolved around the sun. Galileo's observations with his new telescope convinced him of the truth of Copernicus's sun-centered or heliocentric theory.
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Through the telescope, Galileo observed that the surface of the moon appeared pitted with craters. There were mountain peaks lit by the sun's light and other parts that remained in darkness. Galileo then turned his telescope to view the stars, but found that unlike the moon, the stars were hardly magnified. He was... overwhelmed by the hundreds of stars that suddenly became visible. The Milky Way, which to the naked eye had been just a pale uncertain glow, viewed through a telescope was revealed as a myriad of individual stars.
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A few years later in his Letters on the Sunspots (1612), Galileo enumerated more reasons for the breakdown of the celestial/terrestrial distinction. Basically the ideas here were that the sun has spots (maculae) and rotated in circular motion, and, most importantly Venus had phases just like the moon, which was the spatial key to physically locating Venus as being between the Sun and the earth. In these letters he claimed that the new telescopic evidence supported the Copernican theory.
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Galileo's development of a telescope and his unorthodox opinions as a philosopher of science were the central concerns of his career and the subjects of the four writings included in this book. He addressed these writings to contemporary laymen. Stillman Drake's introductory essay places them in their biographical and historical context.
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Galileo used his telescope to show that Venus went through a complete set of phases, just like the Moon. This observation was among the most important in human history, for it provided the first conclusive observational proof that was consistent with the Copernican system but not the Ptolemaic system.
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Through the connections of his friend Paolo Sarpi, Galileo presents an eight-powered telescope to the Venetian Senate. He is rewarded by a doubling of his salary and life- tenure at the University of Padua. He is disappointed by the fine print.
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