Galileo Galilei was peering through a new telescope in 1610 when he noticed something strange: several bright objects flickering around the planet Jupiter that seemed to change positions nightly. His discovery, of moons orbiting Jupiter, was a major crack in the notion, widely held since antiquity, that everything in the universe revolved around the Earth.
The finding, which was condemned by the Catholic Church, helped prove the theory of a sun-centered solar system.
For decades the University of Michigan Library has prized a manuscript related to the discovery, describing it as “one of the great treasures” in its collection. At the top is the draft of a letter signed by Galileo describing the new telescope, and on the bottom are sketches plotting the positions of the moons around Jupiter — “the first observational data that showed objects orbiting a body other than the earth,” the library described it.