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.
Using the new technology of the telescope, Galileo discovered the  moons of Jupiter: Io, Europa, Calisto, and Ganymede, thus proving  that not all things orbit around the Eaâ¦rth, lending great support  to the Copernican model of the heliocentric system. These four  moons are called the Galilean moons to this day.