26 December

Marius was a German astronomer, a pupil of Tycho Brahe, who named Io, Europa, Ganymede and Callisto, the four largest moons of Jupiter. The names are those of mythological figures with whom Jupiter fell in love. Marius was one of the earliest users of a telescope.

A dispute arose when Italian astronomer Galileo Galilei also claimed to have discovered them, about 1610, but is probable they made the discoveries independently.