A simplified illustration of the parallax of an object against a distant background due to a perspective shift. When viewed from Viewpoint A, the object appears to be in front of the blue square. When the viewpoint is changed to Viewpoint B, the object appears to have moved in front of the red square.
From top to bottom: Io, Europa, Ganymede, Callisto. The Galilean moons are the four largest moons of JupiterâIo, Europa, Ganymede, and Callisto. They were discovered by Galileo Galilei around January 1610 and were the first group of objects found to orbit another planet. Their names derive from the lovers of Zeus.
Jupiter has at least 69 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a diameter greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter.