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Why did Galileo conclude that Jupiter has four moons travelling around?
At the time he viewed Jupiter there were only four moons visible to him. I suspect the the others were probably just in orbit on the side of Jupiter opposite Galileo's telescope view.
Before Galileo observed that Jupiter had moons of its own, the prevailing theory in astronomy was that everything in the universe revolved around the Earth, a philosophy known as geocentrism. In...