Simon Marius (1573-1624), German astronomer. Marius, independently of Galileo, discovered the four major moons of Jupiter. In his work Mundus Jovialis (The world of Jupiter, 1614) he gave them the names they are known by today; Io, Europa, Ganymede and Callisto. He was an early user of telescopes, using them to study the Andromeda galaxy. This portrait, from 1614, is said to include the first image of a telescope (across bottom).