The Planet Neptune is the eighth planet from the sun. It is also known as the Blue Giant. Neptune is the fourth and outermost of the gas giant planets and also has rings. Its atmosphere is mostly hydrogen and helium. In Roman mythology Neptune was the god of the Sea. HAPPY BIRTHDAY PLANET NEPTUNE On 12 July 2011, Planet Neptune celebrated its first birthday since its discovery on 24 Sept 1846. It was exactly 1 Neptunian year (164.79 Earth years) on its birthday. Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. It was the last stop in 1989 for the Voyager 2 spacecraft on its grand tour of the solar system. Recent knowledge has been gained by ground-based telescopes and the Hubble Space Telepscope. Due to Pluto's eccentric orbit, Neptune at times becomes the most distant planet from the Sun for a few years. Planet Neptune Facts: Mass: 17.15 Earth-masses Number of known satellites: 13 Length of Year: 164.8 Earth-years Mean Distance from the Sun: 4,500 million kilometers Mean Orbital Velocity: 5.4 kilometers per second Length of Day: 16.11 hours, 0.67 Earth-day Equatorial diameter: 49,500 kilometersAtmospheric components: 74% hydrogen, 25% helium, 1% methane Moons of Planet Neptune Neptune has 13 known moons: Triton, Thalassa, Naiad, Despina, Galatea, Larissa, Proteus and Nereid Triton has the coldest temperatures in the solar system. Voyager observed geysers.Name Neptune is named after the Roman god of the sea. The Great Dark Spot Voyager 2 observed the Great Dark Spot. Recent observations made with the Hubble Space Telescope indicate that the Great Dark Spot no longer exists. Atmosphere Neptune's atmosphere is made up of hydrogen, helium, and methane. Like Earth's atmosphere, Neptune's has clouds and storm systems that revolve around the planet, but with wind speeds of 300 m/sec (700 miles/hr) and clouds of frozen methane. Rings Neptune has six rings which circle the planet. Neptune's rings have been given names: the outermost is Adams (which contains three prominent arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago) and finally the faint but broad Galle. History In 1613 Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. Neptune was first observed by Johann  Galle and Heinrich D'Arrest 23 September 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. On 12 July 2011, Planet Neptune celebrated its first birthday since its discovery on 24 Sept 1846. It was exactly 1 Neptunian year (164.79 Earth years) on its birthday.