Galileo was the first scientist to do what

I mean, he was the first astronomer to observe the sky systematically using a telescope so he discovered it. Hope that helps. ☺

Of all of his telescope discoveries, he is perhaps most known for his discovery of the four most massive moons of Jupiter, now known as the Galilean moons: Io, Ganymede, Europa and Callisto. When NASA sent a mission to Jupiter in the 1990s, it was called Galileo in honor of the famed astronomer !!

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