Galileo Galilei was an Italian physicist and astronomer.  He was born in  Pisa on February 15, 1564. Galileo's father, Vincenzo Galilei, was a  well-known musician. Vincenzo decided that his son should become a  doctor.

In 1581, Galileo was sent to the University of Pisa to study  medicine.  While a student at the university, Galileo discovered that he  had a talent for mathematics.  He was able to persuade his father to  allow him to leave the university to become a tutor in mathematics.  He later  became a professor of mathematics.

In 1609, Galileo heard about the invention of the spyglass, a device which made  distant objects appear closer. Galileo used his mathematics knowledge and  technical skills to improve upon the spyglass and build a telescope. Later  that same year, he became the first person to look at the Moon through a  telescope and make his first astronomy discovery. He found that the Moon was  not smooth, but mountainous and pitted - just like the Earth! He subsequently  used his newly invented telescope to discover four of the moons circling  Jupiter, to study Saturn, to observe the phases of Venus, and to study sunspots on the Sun.

Galileo's observations strengthened his belief in Copernicus' theory that Earth and all other planets revolve around the Sun. Most people in Galileo's time believed that the Earth was the center of the universe and that the Sun and planets revolved around it.

The Catholic Church, which was very powerful and influential in Galileo's  day, strongly supported the theory of a geocentric, or Earth-centered,  universe. After Galileo began publishing papers about his astronomy  discoveries and his belief in a heliocentric, or Sun-centered, Universe, he  was called to Rome to answer charges brought against him by the Inquisition  (the legal body of the Catholic Church). Early in 1616, Galileo was accused  of being a heretic, a person who opposed Church teachings. Heresy was a crime  for which people were sometimes sentenced to death. Galileo was cleared of  charges of heresy, but was told that he should no longer publicly state his  belief that Earth moved around the Sun. Galileo continued his study of  astronomy and became more and more convinced that all planets revolved around  the Sun.  In 1632, he published a book that stated, among other things, that the  heliocentric theory of Copernicus was correct.  Galileo was once again  called before the Inquisition and this  time was found guilty of heresy.  Galileo was sentenced to life  imprisonment in 1633.  Because of his age and poor health, he was allowed to  serve his imprisonment under house arrest.  Galileo died on January 8, 1642.