Neptune is a gaseous planet made of hydrogen and helium. It is very like Uranus but it is largely blue in color due to the composition of its atmosphere. Neptune has a very active atmosphere with high-speed winds that swirl around the planet faster than it rotates. The winds carry “scooter clouds” around the planet at speeds of 1,500 miles per hour (2,400 km/h). Neptune’s orbit sometimes extends beyond the orbit of Pluto, as it did from 1979 to 1999. Neptune has two large moons, Triton and Nereid. Triton, one of the largest moons in the Solar System, is unusual because it moves in a circular orbit from east to west.

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Picture of the Great Dark Spot by Voyager. The white clouds around the Great Dark Spot suggests that the Great Dark Spot rotates counterclockwise.

Click on the picture to get a larger image of picture.

PLANET DISCOVERIES Astronomers predicted the existence of another planet beyond Uranus before it was finally discovered by a German, Johann Galle, in 1846. They had noticed that Uranus was not staying in a completely stable orbit around the Sun, and suspected that it was being pulled slightly off course by the gravity of another body. Mathematicians calculated where this possible planet might be, and Neptune was found in almost the exact spot predicted by Galle.

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