================================================================ \newslide{51} Galileo Galilei (1564-1642) in his early forties, a few years before the beginning of his groundbreaking telescopic observations in 1609. Prior to 1609, Galileo had only shown passing interest in astronomical matters, despites privately presenting himself as a Copernican. His work up to then was mostly concerned with the problem of motion, in particular motion on inclided planes, of the pendulum, and of freely falling bodies. First little known outside of Italy, Galileo taught mathematics and astronomy at Pisa from 1589 to 1592, and then at Pisa from 1592 to 1610, when his telescopic discovery propelled him into international fame, and won him a position at the Florentine Court, as chief mathematician and philosopher to the Grand Duke of Tucsany, Cosimo de Medici {I}{I}. Reproduced from {\sl The Cambridge illustrated History of Astronomy}, ed.~M.~Hoskin (1997). \newslide{54} Drawings of the moon as seen with Galileo's telescope. Comparing patterns of light and shadow in the vicinity of the terminator (dividing line between light and shadow) at first and third quarter, Galileo could argue convincingly that there exists mountains and valleys on the lunar surface. Aristotelian doctrine stipulated that celestial bodies were perfectly smooth and spherical. Source: Galileo's 1610 {\it Sidereus Nuncius}. Reproduced from {\sl The General History of Astronomy}, vol.~2A, 1989, chap.~6. \newslide{58} Title page of Galileo's {\it Sidereus Nuncius}, published in Venice in 1610. The book instantly made Galileo a European celebrity, and earned him, in July 1610, the position of chief mathematician and philosopher mathematician to the Grand Duke of Tucsany, Cosimo de Medici {I}{I}, in Florence. Reproduced from the introductory essay in A.~van Helden's 1989 translation. \newslide{70} Title page of Galileo's {\it Letters on Solar Spots}, published in Rome in 1613. The letters were addressed to Augsburg magistrate Mark Wesler (1558--1614), in response to the three letters to the same Wesler written by Scheiner. From 1613 on, all of Galileo's books were written in the vernacular Italian, rather than Latin. This was deemed distasteful by many professional astronomers, and downright dangerous by the Roman Catholic Church. Reproduced from {\sl The history of the discovery of the solar spots}, in {\sl Popular Astronomy}, W.M.~Mitchell, 1916. \newslide{83} Title page of Galileo's Dialogue concerning the two chief world systems, published in Florence in 1632. This is usually considered as Galileo's masterpiece. Despites ostensible claims to the contrary, the Dialogue represents Galileo's strongest endorsement of the Copernican system over its Ptolemaic counterpart, and makes devastating refutations of many central tenets of Aristotelian Physics. Reproduced from S.~Drake's 1967 translation. \newslide{84} Galileo before the Roman Inquisition. On June 22 1633 Galileo was forced to kneel in front of the Inquisition and recant his beliefs in the Copernican doctrine and the motion of the Earth. He was then sentenced to life imprisonment, which was almost immediately commuted to perpetual house arrest without visitors, ostensibly for having disobeyed a 1616 injunction by Bellarmino ``...not to defend or teach the Copernican doctrine...''. Galileo's {\it Discourse} was put on the Index, as well as Kepler's and Copernicus' books. Those books were removed from the Index in 1835, and only in 1992 did the Roman catholic Church formally admitted to having erred in dealing with Galileo. 1857 Painting by Cristiano Banti, reproduced from {\sl Galileo Heretic}, P.~Redondi, 1987. \newslide{85} Galileo at age 70 and under permanent house arrest at his home in Arcetri. His sentence was upheld rather rigidly despites numerous appeals to the Inquisition and the Pope by Galileo himself, as well as numerous prominent scientists and statemen in Italy and Europe. After Galileo became blind in 1637, the enforcement of his sentence was relaxed somewhat, and he was allowed to receive visitors for extended periods of time. He died on the evening of January 8, 1642. The Roman ecclesiastic authorities vetoed the public funeral and honor planned by the Florentine state. Detail of 1635 portrait by Justus Sustermans, now at the Galleria degli Uffizi in Florence. \medskip \ref{Drake, S.~1978, {\sl Galileo at work: his scientific biography}, Chicago: The University of Chicago Press (1995 Dover reprint)} \medskip \ref{Drake, S.~1957, {\sl Discoveries and Opinions of Galileo} (including a translation of the {\sl Letters on Sunspots}), New York: Doubleday $(\ast)$}
Galileo, G. 1610, Sidereus Nuncius, trans. A. van Helden 1989, The University of Chicago Press.
Galileo, G. 1613, Letters on Sunspots [in S. Drake (trans.) 1957, Ideas and Opinions of Galileo, Doubleday].
Galileo, G. 1632, Dialogues concerning the two chief world systems, trans. S. Drake, 2nd edition 1967, University of California Press
De Santillana, G. 1955, The crime of Galileo, The University of Chicago Press