1564-1642. Italian astronomer and physicist. He studied at the University of Pisa, and after teaching at Siena and Florence returned to Pisa as professor of mathematics (1589). Two years later, because of his opposition to Aristotelianism, he moved to the University of Padua. Here he conducted mechanical research, made mathematical instruments for sale, and wrote several articles that were circulated in manuscript to his pupils and friends. In 1610, with the aid of his newly invented telescope, he discovered four moons that revolve around Jupiter. By analogy he reasoned that the planets revolve about the sun. This led him to support the Copernican explanation of the solar system. He also noted in his book The Starry Messenger many other observations which could not be accounted for with the Ptolemaic view of the universe. His publication of these ideas gained him Europe-wide fame, and appointment as philosopher and mathematician to the duke of Tuscany.
He also came into conflict with the Inquisition,* and when the Copernican theory was condemned Galileo was forbidden to teach it (1616). In 1624 he visited Rome and obtained permission to write on the Copernican and Ptolemaic systems provided that the treatment was impartial. The book which resulted from his work, Dialogue Concerning the Two Chief Systems of the World (1632), caused him to be brought to trial by the Inquisition. The work was condemned, Galileo recanted, and he was sentenced to life imprisonment. He was, however, permitted to live under house arrest till his death.
G. de Santillana, The Crime of Galileo (1955); L. Geymonat,(tr. S. Drake, 1965); C.L. Golino (ed.), Galileo Reappraised (1966).