Portrait of Galileo Galilei Courtesy of Ottavio Leoni, Reunion des Musees Nationaux

Galileo Galilei was an Italian astronomer and physicist who lived between 1564-1642. He was the first person to use a telescope to look at the heavens, and discovered craters in the moon.

Galileo found craters on the moon, and sunspots on the sun. This showed that the heavens weren't perfect, as Aristotle had said. This offended the Roman Catholic Church, and Galileo spent the later years of his life under house arrest.