Galileo was born near Pisa, on February 15, 1564. His father, Vincenzo Galilei, played an important role in the musical revolution from medieval polyphony to harmonic modulation. Galileo was taught by monks at Vallombrosa and then entered the University of Pisa in 1581 to study medicine. He soon turned to philosophy and mathematics, leaving the university without a degree in 1585. For a time, he tutored privately and wrote on hydrostatics and natural motions, but he did not publish them. In 1589 he became a professor of mathematics at Pisa, where he is reported to have shown his students the error of Aristotle’s belief that speed of fall is proportional to weight, by dropping two objects of different weight simultaneously from the Leaning Tower
At Padua, Galileo invented a calculating “compass” for the practical solution of mathematical problems. He turned from speculative physics to careful measurements, discovered the law of falling bodies and of the parabolic path of projectiles, studied the motions of pendulums, and investigated mechanics and the strength of materials. He showed little interest in astronomy, although beginning in 1595 he preferred the Copernican theory (sun centered theory)—that the earth revolves around the sun. Only the Copernican model supported Galileo’s tide theory, which was based on motions of the earth.
In 1609 he heard that the Dutch had invented a spyglass, what is now called a telescope. In August of that year he presented a telescope, about as powerful as a modern field glass with a magnification of about 40. He also saw that the Milky Way was composed of stars, and he discovered the four largest moons of Jupiter. He published these findings in March 1610 in The Starry Messenger. His new fame gained him appointment as court mathematician at Florence. He was thereby freed from teaching duties and had time for research and writing. By December 1610 he had observed the phases of Venus, which contradicted Ptolemaic astronomy and confirmed his preference for the Copernican system.
The professors of philosophy scorned Galileo’s discoveries because Aristotle had held that only perfectly spherical bodies could exist in the heavens and that nothing new could ever appear there. Galileo also disputed with professors at Florence and Pisa over hydrostatics, and he published a book on floating bodies in 1612.
In 1624 Galileo began a book he wished to call “Dialogue on the Tides,” in which he discussed the Ptolemaic and Copernican hypotheses in relation to the physics of tides. In 1630 Roman Catholic censors at Rome licensed the book for printing, but they altered the title to Dialogue on the Two Chief World Systems (trans. 1661). It was published at Florence in 1632. Despite two official licenses, Galileo was summoned to Rome by the Inquisition to stand trial for “grave suspicion of heresy.” This charge was grounded on a report that Galileo had been personally ordered in 1616 not to discuss Copernicanism either orally or in writing. Cardinal Bellarmine had died (the person that told Galileo not to teach or defend the heliocentric theory), but Galileo produced a certificate signed by the cardinal, stating that Galileo had been subjected to no further restriction than applied to any Roman Catholic under the 1616 edict. The church called him to court in 1633 and questioned him. Finally, at almost 70 years of age, Galileo gave in and agreed that the earth does not move around the sun, but legends say that he muttered the words “Eppur si muove (and yet it does move.)” to himself.
Galileo’s most valuable scientific contribution was his founding of physics on precise measurements rather than on metaphysical principles and formal logic. More widely influential, however, were The Starry Messenger and the Dialogue, which opened new vistas in astronomy. Galileo’s lifelong struggle to free scientific inquiry from restriction by philosophical and theological interference stands beyond science.

Works Cited
Balcer, Jake M. “Galileo” Encyclopedia of World Biography: volume 1
“Galileo” UXL Biographies
Stillman, Drake “Galileo” Microsoft Encarta Encyclopedia. 1998
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