Neptune

The existence of the eighth planet was revealed to humans in the year 1846. Who discovered Neptune? Was it John C. Adams or Urbain Leverier? I guess the answer to that depends on whether you are French or a loyal British subject. Although the first person to see Neptune, and know that it was a planet, was Johann Galle.

Here are some of the essential facts about Neptune:

Radius 24,300 km which is about four times the size of Earth
Rotation 16 hours 5 minutes at the equator. Here is a neat movie.
Revolution 165 years to orbit the Sun
Semi major axis 30.06 A.U.
Atmosphere Mostly hydrogen and some helium, with an interior of ices and rock.
Cloud Features Dark Belts alternate with bright Zones, they are different shades of blue. The Great Dark Spot was present in 1989 when Voyager II passed by, but more recent views from the Hubble Space Telescope reveal that the spot has since faded.
Moons or rings Dark, icy rings which are not complete circles but rather 'arcs'. The big moon Triton has a very thin atmosphere. Here is a nice movie about Triton.
Space Probes Neptune has been visited by Voyager II and no other probe.

There is an interesting theory that carbon might be crystallizing into diamonds inside Neptune and Uranus. Try this site for more information on Neptune!

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Updated November 19, 2009