Galileo, Italian physicist and astronomer, was born at Pisa February 15, 1564 and died at Arcetri, near Florence, January 8, 1642. In 1581 he entered the University of Pisa to study medicine and the Aristotelian philosophy, but soon abandoned medicine for mathematics and physical science.

He studied at Pisa, where he later held the chair in mathematics from 1589 - 1592. He was then appointed to the chair of mathematics at the University of Padua, where he remained until 1610. During these years he carried out studies and experiments in mechanics, and also built a thermoscope. He devised and constructed a geometrical and military compass, and wrote a handbook which describes how to use this instrument.

At the age of 19 he discovered the principle of isochronism- that each oscillation of a pendulum takes the same time despite changes in amplitude. Soon thereafter he became known for his invention of a hydrostatic balance and his treatise on the center of gravity of falling bodies. He found experimentally that bodies do not fall with velocities proportional to their weights, a conclusion received with hostility because it contradicted the accepted teaching of Aristotle. Galileo discovered that the path of a projectile is a parabola, and he is credited with anticipating Isaac Newton's laws of motion.

In 1594 he obtained the patent for a machine to raise water levels. He invented the microscope. In 1604 Galileo learned of the invention of the telescope in Holland. From the barest description he constructed a vastly superior model. With it he made a series of profound discoveries, including the moons of planet Jupiter and the phases of the planet Venus (similar to those of Earth's moon).

In 1610 he was nominated the foremost Mathematician of the University of Pisa and given the title of mathematician to the Grand Duke of Tuscany, Cosmo II. In 1611 he went to Rome. He became a member of the Accademia dei Lincei and observed the sunspots. In 1612 he began to encounter serious opposition to his theory of the motion of the earth that he taught after Copernicus.

In 1632 he published his Dialogue Concerning the Two Chief World Systems, a work that upheld the Copernican System rather than the Ptolemaic System and marked a turning point in scientific and philosophical thought.

In October of 1632 he was summoned by the Holy Office to Rome. The Inquisition tribunal passed a sentence condemning him and compelled Galileo to renounce all his beliefs and writings supporting the Copernican theory.

He was sent to exile in Siena and finally, in December of 1633, he was allowed to retire to his villa in Arcetri, the Gioiello. His health condition was steadily declining, - by 1638 he was completely blind, and also by now bereft of the support of his daughter, Sister Maria Celeste, who died in 1634. Galileo died in Arcetri on 8 January 1642, the year of Newton's birth.

Galileo's chief contributions to science are his formulation of the laws governing failing bodies, the refinement of the telescope, the discovery of the isochronism of the pendulum, and numerous astronomical discoveries. His works were stricken from the Index in 1835. The most important are The System of the World, in Four Dialogues (Florence, 1632); and Mathematical Discourses and demonstrations touching two new Sciences (Leyden, 1638).

Galileo's originality as a scientist lay in his method of inquiry. First he reduced problems to a simple set of terms on the basis of everyday experience and common-sense logic. Then he analyzed and resolved them according to simple mathematical descriptions. The success with which he applied this technique to the analysis of motion opened the way for modern mathematical and experimental physics. Isaac Newton used one of Galileo's mathematical descriptions, "The Law of Inertia," as the foundation for his "First Law of Motion."

Sources:

http://galileo.imss.firenze.it/museo/b/egalilg.html

http://www2.lucidcafe.com/lucidcafe/library/96feb/galileo.html

http://www.utm.edu/research/iep/g/galileo.htm