Galileo observing Jupiter's moons. Illustration of the four largest moons of Jupiter, as observed by Italian astronomer Galileo Galilei (1564-1642) in March 1612. He had first discovered these moons in 1610, using telescopes he had built himself. This was the first discovery of heavenly objects that did not orbit the Earth. This challenged existing views that held the Earth to be at the centre of the universe. The moons are named the Galilean moons in Galileo's honour. Jupiter is the large circle, while the four moons (Europa, Io, Ganymede and Callisto) are the dots either side. Galileo published his observations in 'Istoria e Dimostrazioni' (1613).