Galileo discovered evidence to support Copernicus’ heliocentric theory when he observed four moons in orbit around Jupiter. Beginning on January 7, 1610, he mapped nightly the position of the 4 “Medicean stars” (later renamed the Galilean moons). Over time Galileo deduced that the “stars” were in fact moons in orbit around Jupiter.

Pop Culture Resources Saturn’s largest moon Titan is an extraordinary and exceptional world. Among our solar system’s more than 150 known moons, Titan is the only one with a substantial atmosphere.

Planet Mars: Click (or touch) and drag to interact with this 3D model of Planet Mars. View and print the more detailed Mars Facts ›