Through his telescope, Italian astronomer Galileo Galilei made the first observation of Jupiter's Galilean moons: Io, Europa, Ganymede and Callisto, although he was not able to distinguish the first two until the following night.

Italian astronomer Galileo Galilei (pictured) demonstrated his first telescope to Venetian lawmakers.

Galileo Galilei became the first person to observe the planet Neptune (pictured), although he mistakenly catalogued it as a fixed star.