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Neptune

An image of Neptune made by Voyager 2 in August 1989. The Great Dark Spot, with The Scooter, a white patch just beneath it, are...Read More >>An image of Neptune made by Voyager 2 in August 1989. The Great Dark Spot, with The Scooter, a white patch just beneath it, are visible in the planet's southern hemisphere, on the left of the globe. Neptune is the eighth planet from the Sun—the most distant of the true planets. Grouped with Uranus as one of the two "ice giants", it is the fourth largest planet in the Solar System. Little was known about Neptune until Voyager 2 paid it a visit in 1989. The bluest planet in the Solar System, like Uranus it is almost completely featureless, although clouds and storms can sometimes be seen on its surface. Neptune has 14 known moons. Triton, the only one that is spherical rather than irregular in shape, is by far the largest of them.



Voyager 2's image of Neptune's moon Triton

Discovery

Neptune was first observed by German astronomer Johann Galle in September 1846, following key calculations to pinpoint its position almost exactly made by the French mathematician, Urbain Le Verrier. Noting that Uranus was being pulled slightly off course, French astronomer Alexis Bouvard had in 1821 concluded that the pull of gravity from another large planet farther away from the Sun was responsible. British astronomer John Couch Adams independently calculated where Neptune would be at roughly the same time, but Le Verrier is usually credited with the planet's discovery.

The first person to observe Neptune was Galileo, in 1612. But he mistook Neptune for a star. Galileo seems to have noticed that the "star" he saw had moved relative to the other stars around it.

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