Galileo Spots Jupiter's Moons: Universe Shakes
Three faint specks of light near Jupiter kept shifting positions, and Galileo could not explain why. Over several nights of observation through his homemade telescope, he realized these were not background stars but satellites orbiting Jupiter itself. A fourth moon appeared shortly after. This was devastating to Aristotelian cosmology, which held that everything in the heavens revolved around Earth. Here was proof of a second center of motion in the universe, an unmistakable demonstration that celestial bodies could orbit something other than our planet. The Catholic Church initially celebrated Galileo's findings before recognizing their theological implications. The four moons, now called the Galilean satellites, became the cornerstone evidence for Copernican heliocentrism and launched the telescopic revolution that remade astronomy.
January 7, 1610
416 years ago
Key Figures & Places
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