Galileo Galilei was born on February 15, 1564 in Pisa, Italy. In 1570 his family relocated to Florence. Galileo pioneered "experimental scientific method" and was the first to use a refracting telescope to make important astronomical discoveries.
In 1581, Galileo studied at the University of Pisa. There he became interested in the workings of science and concluded that the period (the time in which a pendulum swings back and forth) does not depend on the arc of the swing (the isochronisms).
In 1609 Galileo learned of the invention of the telescope in Holland. From the barest description he constructed a vastly superior model. Galileo made a series of profound discoveries using his new telescope, including that the moon has craters, valleys, and mountains much like the Earth’s terrain. He also was able to see four small lights orbiting around the planet Jupiter. He was then able to conclude that it too was moons. Galileo was also able to discover that the planet Venus had phases much like our Moon.
As a professor of astronomy at University of Pisa, Galileo was required to teach the accepted theory of his time that the sun and all the planets revolved around the Earth. Later at University of Padua he was exposed to a new theory, proposed by Nicolaus Copernicus, that the Earth and all the other planets revolved around the sun. Galileo's observations with his new telescope convinced him of the truth of Copernicus's sun-centered or heliocentric theory.
In 1610, Galileo published a book, The Starry Messenger, describing his findings that supported the Copernican theory. Galileo's support for the heliocentric theory got him into trouble with the Roman Catholic Church. He was forced to abandon his astronomical pursuits. But, Galileo retaliated by publishing a book, Dialogue Concerning the Two Chief World Systems. This book cause more arguments with the church due to it were in Italian which was a direct conflict with the church. In 1633 the Inquisition convicted him of heresy and forced him to recant (publicly withdraw) his support of Copernicus. They sentenced him to life imprisonment, but because of his advanced age allowed him serve his term under house arrest at his villa outside of Florence, Italy. It was not until 1992 that the church publicly forgave Galileo. But due to the timeframe, the damage had already been done.
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." Galileo died in 1642, the year of Newton's birth.