Today in Astronomy

NASA/JPL/DLR

January 7, 1610

Galileo Galilei observes the four largest moons of Jupiter for the first time. He named them and in turn the four are called the Galilean moons. Jupiter's 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). From the top, they are Io,Europa, Ganymede and Callisto