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Events on Thursday 7 January 1610 1
1610Discovers the four moons of JupiterIdentifies the Galilean moonsOn the night of January 7, 1610, Galileo observed three (and shortly after, a fourth) small "stars" moving alongside Jupiter, quickly realizing they were satellites orbiting the planet. The discovery of what are now called the Galilean moons—Io, Europa, Ganymede, and Callisto—provided the first direct observational evidence that not all celestial bodies orbited the Earth. It was a significant blow to the geocentric model and strong circumstantial support for Copernican theory.