Galileo Sees Jupiter's Moons

January 7, 1610

Pointing his improved telescope at Jupiter, Galileo noticed four small stars arranged in a line that shifted from night to night. Within a week he realized they were moons, orbiting another world. The Copernican system suddenly had visual proof, and the universe had just grown unignorably stranger. He named them the Medicean stars, flattering his Florentine patrons.