Galileo Galilei was born in Pisa, Italy, in 1564. He studied in Pisa and Padua, and later was appointed to chair of the mathematics department at the University of Padua, where he remained until 1610. Perhaps his most well known achievement was the construction of his own telescope. This creation led him to discover the four largest moons of Jupiter, craters on the moon, sunspots, and the phases of Venus -- a finding that supported Copernicus' theory that the sun is the center of the solar system. In addition to astronomical discoveries, he constructed revolutionary theories in physics. By studying the pendulum and other bodies in motion, Galileo showed that all bodies fall at the same rate, and that motion can only be altered by the application of a force (the law of inertia.) He also proposed Galilean relativity, which states that the same definitions of motion apply everywhere. (This law is valid for low speeds but must be revised at speeds approaching that of light.) Galileo's Copernican view was not popular with the Church, however, and in 1633 he was forced to recant his beliefs. Watched carefully by officers from the Inquisition, he continued to write on mathematics and the design of a pendulum clock until his death in 1642.