Galileo Galilei (1564-1642), Italian astronomer and physicist. Galileo is famed for his 1610 use of his telescope to discover the four largest moons of Jupiter. He also observed mountains on the Moon. In physics, he found that all pendulums swing with the same time period, and that heavy and light objects fall at the same rate. He supported the Copernican theory that the Sun, rather than the Earth, was at the centre of the solar system. This belief was declared heretical in 1633 by the Inquisition of the Roman Catholic Church. He was held under house arrest for the rest of his life. Engraving from Vies des Savants Illustres (1876).