Neptune, predicted to exist by the English astronomer and mathematician John Couch Adams when aged 24, was discovered in 1846 by Galle (a German) and d’Arrest (a Dane). Neptune’s blue colour (caused by the absorption of red light by atmospheric methane) led it to be named after the Roman god of the sea, (in Greek, Poseidon). Due to the highly eccentric orbit of Pluto, Neptune is, at some times, the most distant planet from the Sun. Voyager 2 visited the planet in 1989 and is the source of most of our knowledge of the planet and its moons. Prior to Voyager only 2 moons were known; now 8 have been named. Other small moons almost certainly await discovery.