Neptune
Neptune is usually the 8th planet from the sun, but sometimes it is the farthest. Every 246 years, for 20 years, Pluto moves inside Neptune’s orbit, making it the farthest planet from the sun. Pluto moved into Neptune's orbit in 1979, it came out in 1999. Neptune  was named after the Roman god of the sea (wonder why). Its 30 times farther away from the sun then Earth! Neptune’s average distance from the sun is 4, 500, 000, 000 km. It is one of the two planets you need a telescope to see here on Earth. Scientist doubt there is any life on Neptune.
Neptune's orbit takes 165 years to go around the sun once! It travels very slow. Only six km/sec, Earth travels 30km/sec. Neptune hasn't made one full rotation around the sun since it's discovery! It will make it full rotation in 2011. Neptune's axis is tilted at 29deegres.Its day lasts 16hours and 17min  and its summers and winters last 40 years each! Imagine, 40 years of summer!
Neptune has an atmosphere (like Uranus) of 83% hydrogen, 15%Helium and 2% methane. The methane gives Neptune its blue colour. Neptune receives 1/1000 heat of what we receive here on Earth. It also radiates twice as much heat as it receives. Its thick atmosphere doesn't contain only blue clouds, but also white ones! On Neptune the wind speeds can reach up to 2000km/h. Those are the fastest winds in the solar system! The temperature on Neptune is -218 degrees.
Neptune has 8 known moons. The biggest is Triton (27, 000km wide) and the smallest is Naiad (58 km wide). Only two moons (Triton and Nereid) can be seen here on Earth.  Voyager 2 discovered the others. In order going away from Neptune is Naiad, Thalassa, Despina, Galatea, Larissa, Porteus, Triton, and Nereid. In order from smallest to biggest is Naiad, Thalassa, Despina, Galateo, Larissa, Nereid, Porteus and Triton. A strange thing about Triton is that is rotates the opposite way of the planet. It’s the only major moon that does that! Triton travels around Neptune every six days. Do you know where the coldest spot in the solar system is? Its on Triton, the temperature there is -235 degrees Celsius. Most people would think it was Pluto!
Neptune has four rings. Like Jupiter and Uranus no one knows what they're made of. The rings are much fainter then Saturn's. The outer ring is brighter and denser then the rest of the rings. Going away from Neptune the rings names are Diffuse, Inner, Plateau and the outermost Main.
Triton, Neptunes biggest moon
Neptune!
The force of some unknown planet was disturbing Uranus's orbit. There had to be another planet! Neptune was discovered by using mathematics, not by looking in a telescope. In 1843 John C. Adams an English astronomer, worked to find the location of the planet. He finished his work in 1845 and sent it to an observatory. The person at the observatory didn't look for the planet, he didn't believe in Adams. Meanwhile, a French astronomer named Urbain J. Leverrier had also predicted the position of the planet. He sent it to an observatory in Germany and.... they found Neptune near the spot he had predicted. There was a big dispute between the English and the French over whom discovered the planet. In the end both get credit because both where correct.
The Voyager 2 is the only spacecraft to ever visit Neptune. It launched in 1977, 12 years later it reached Neptune. Voyager 2 provided the first up close pictures of Neptune, its rings and moons.
The Voyager 2 as it passes Neptune and Triton
Neptune has a diameter of 49, 530km. It is the fourth largest planet, but the smallest gas giant. It is smaller then Uranus in size, but larger in mass. Neptune is almost 4 times the size of Earth and is seventeen times heavier. Neptune is classified with Jupiter, Saturn and Uranus, as Jovian (or giant).
When Voyager 2 passed Neptune, it had a great dark spot in its Southern Hemisphere. The spot was a huge storm as big as Earth, but half the size of Jupiter's Red Spot. Then in 1994 the HTS (Hubble Space Telescope) showed that the spot was gone! Then a few months later the HTS showed Neptune had another spot in Neptune's Northern Hemisphere. This means Neptune's atmosphere changes quickly. Weird isn't it?
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