Galileo's Science/Astronomy
Galileo made important discoveries in astronomy which directly opposed Aristotelian physics and the Ptolemaic system, which was based on Aristotelian principles. He made extensive use of his improved telescopes to observe the night sky. These discoveries were first published in 1610, in his book Sidereus Nuncius (“The Starry Messenger”).
According to Aristotle, the Moon and other heavenly bodies are made of quintessence, which never changes, and are perfectly spherical. Galileo disproved this theory when he observed that the Moon has craters and mountains on its surface with his telescope.
He also observed four satellites revolving around Jupiter, the “Galilean moons.” This opposed Aristotle, who held the theory that everything in the universe orbits around the Earth.