Jupiter has a set of moons
Until the 1600's, Jupiter was simply a bright, slow-moving, wandering star.Galileo discovered that it was a sphere like the Moon and Venus. It shines because it reflects light from the Sun. It os a planet like Earth, that has not one, but four orbiting moons.
The moons Galileo observed are now known to be largest of Jupiter's many moons - over sixty have been catalogued. The four that Galileo discovered are called the Galilean moons: Io, Europa, Ganymede and Callisto.