# Galileo Galileo Galilei (1564-1642), Italian scientist who proved that objects with different masses fall at the same velocity. He was one of the first persons to use a telescope to examine objects in the sky. Authorities of the Roman Catholic Church forced Galileo to renounce his belief in the model of the solar system proposed by Nicolaus Copernicus. Galileo had to assert that the earth stands still, with the sun revolving around it.