AkaSci 🛰️OTD on Jan 7, 1610, Galileo Galilei, using a telescope of his own design, discovered 3 moons of Jupiter - Callisto, Europa and Io. He discovered Ganymede 6 days later.
He observed 3 "stars" around Jupiter, whose positions changed in observations on subsequent nights. On Jan 10, Galileo noted that one of them had disappeared. Within a few days, he concluded that they were "moons" orbiting Jupiter, a discovery that was anathema to the Church at that time.
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