Galileo Galilei: The Telescope, the Method, and the Trial

Galileo Galilei perfected the telescope in 1609, dramatically increasing its power for astronomical observation, and published his first telescopic findings in Sidereus Nuncius (The Starry Messenger) in 1610. His discoveries struck directly at the old cosmology: he found four moons of Jupiter, which he named the 'Medicean Stars' in gratitude to his patrons, proving that not everything orbited the Earth; he observed the phases of Venus, decisive evidence in favor of the heliocentric model; and he observed sunspots and lunar mountains and craters, both of which called into question the supposed unchanging perfection of the celestial bodies.