General Information

Neptune is the eighth planet from the sun and the fourth largest (although its mass is slightly larger than Uranus'). Like the other gas giants, it has an atmosphere rich in hydrogen and helium, but also contains about 1% methane which is responsible for its blue colour. In 1846, French astronomer Urbain Jean Joseph Leverrier calculated that Neptune must exist from perturbations in Uranus' orbit. Johann Gottfried Galle, a German astronomer observed the planet the same year within 1° of its calculated position.

It is not visible with the naked eye, but you may be able to spot it with binoculars if you know where to look. Most of what we know today about Neptune comes from an encounter that Voyager 2 had with the planet in 1989. In 1979, it was actually the farthest planet from the sun, because Pluto's eccentric orbit cut inside that of Neptune. In 1999 it once again placed rank as the eighth planet when Pluto moved back outside of Neptune's orbit.