Galileo Galilei. Portrait of the Italian astronomer Galileo Galilei (1564-1642). Galileo was born at Pisa, where he first studied medicine and later mathematics and physics. His fame was made by his observations through the telescope. In 1610 he observed mountains on the Moon, four satellites of Jupiter and numerous dim stars. In his book Dialogue on the Two Chief World Systems" he discussed Ptolemeic and Copernican (heliocentric) cosmologies. He thought that his discussion was diplomatic, but it was judged heretical by the Inquisition in 1633 and he was sentenced to house arrest for life. His other studies included the dynamics of falling bodies."