Galileo Galilei laid the foundations of several branches of physics and astronomy. He was born in Pisa, Italy, and was tutored privately until 1557 when the family moved to Florence where he studied at a monastery. After six years, he returned to Pisa to study medicine at the University, but left without a degree and returned home in 1585. It was however, while in Pisa that Galileo became interested in mathematics and physics and thus set the course for the rest of his life. In 1582 he noted that the period of a swinging pendulum was always the same, no matter how long the swing was. It is said that he discovered this while he was watching a lamp swinging in Pisa Cathedral, and although he recognized that the swing was regular, he did not develop the idea of a time-keeping device until much later.
In 1589 he became Professor of Mathematics at the University of Pisa and it was around that time that he allegedly conducted an experiment in which he dropped two cannon balls of differing masses from the leaning tower of Pisa to show that their rate of fall would be the same. This work on falling bodies was continued when he became Professor of Mathematics at Padua in 1592. Here he refined his ideas and understanding of falling bodies and acceleration (1604). He understood that his law of falling bodies would only work in a vacuum and that air resistance on a body causes it to reach a terminal velocity. He also showed that a projectile had both a vertical and horizontal component of velocity and that its trajectory is a parabola.
Galileo's work on mechanics was interrupted in 1609 when he heard about a telescope that had been developed in Holland. He set about constructing his own telescope and used it to study the sky. Within two years of completing the telescope he had made some astounding discoveries, confirming the existence of four moons orbiting Jupiter, observing Sun spots and the Milky Way. In 1610, he published much of this work to great acclaim all round Europe.
He continued to work in Florence as mathematician and philosopher to the Grand Duke of Tuscany, turning his thoughts to hydrostatics in 1612. His view that the Earth revolved around the Sun (a Copernican theory) was opposed by the Church leaders who deemed his ideas heretical. He continued to study mechanics and astronomy, but did not publicly support the Copernican theory, until Pope Urban III allowed Galileo to present the views of the geocentric and heliocentric systems (1624). The subsequent book was immediately banned and Galileo summoned to Rome to face trial in 1633. He was sentenced to life imprisonment for his beliefs, but was later allowed to live under house arrest in Florence where he continued his work. He later became blind, but continued to work until his death, designing a pendulum clock. The sentence passed on him was formally retracted in 1992 by Pope John Paul II.
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