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.
Galileoâs Discovery. Jupiter was observed by Galileo Galilei on January 7, 1610. Not only was he able to discover the planet he was also able to discover three of the many moons orbiting it. On January 13 of the same year, which is only six nights after, he discovered a fourth moon. The four moons were later dubbed the Galilean Moons.