1. Callisto
2. Europa
3. Ganymede
4. Io
* As of March 23, 2023, the planet Jupiter had 95 known moons. In a YouTube video uploaded May 15, 2015, at that time, acccording to the presenter, there were 67, but he added the rider it depends how small an object you are prepared to call a moon. When I was at school, there were 12.
The Voyager 1 space probe also discovered Jupiter has rings, although they are much fainter than the truly spectacular rings of Saturn.
The four above, listed in alphabetic order, are known as the Galilean Moons. They were first confirmed as such by Galileo in 1609/10. The German astronomer Simon Mayer is said to have observed them independently about the same time. It is possible indeed likely that some people with extremely acute eyesight saw 1 or all 4 before this, although they would not have realised what they are, but all credit must go to Galileo, especially in view of the shoddy way he would later be treated by the Catholic Church.
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