Neptune (astronomy)

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Eighth planet in average distance from the Sun. It is a giant gas (hydrogen, helium, methane) planet, with a mass 17.2 times that of Earth. It has the fastest winds in the Solar System.

Mean distance from the Sun
4.4 billion km/2.794 billion mi

Equatorial diameter
48,600 km/30,200 mi

Rotation period
16 hours 7 minutes

Year
164.8 Earth years

Atmosphere
methane in its atmosphere absorbs red light and gives the planet a blue colouring. Consists primarily of hydrogen (85%) with helium (13%) and methane (1–2%)

Surface
hydrogen, helium, and methane. Its interior is believed to have a central rocky core covered by a layer of ice

Satellites
thirteen moons were known by the end of 2005. Of these, seven had been discovered with telescopes on Earth. The other six were discovered by the Voyager 2 probe in 1989. One of these, Proteus (diameter 415 km/260 mi), is larger than Nereid (300 km/200 mi), which had previously been discovered from Earth. Nereid orbits every 360 days on a highly elliptical path. The largest moon, Triton, is one of the four largest moons in the solar system. It orbits every 5.9 days in an east-to-west retrograde direction and is thought to be similar in nature to the dwarf planet Pluto.

Rings
there is a system of faint rings: Galle, Le Verrier, Lassell, Arago, and Adams (in order from Neptune). Galle is the widest at 1,700 km/1,060 mi.

Neptune was located in 1846 by German astronomers Johan Galle and Heinrich d'Arrest after calculations by English astronomer John Couch Adams and French mathematician Urbain Le Verrier had predicted its existence from disturbances in the movement of Uranus. Voyager 2, which passed Neptune in August 1989, revealed various cloud features, notably an Earth-sized oval storm cloud, the Great Dark Spot, similar to the Great Red Spot on Jupiter, but images taken by the Hubble Space Telescope in 1994 showed that the Great Dark Spot had disappeared. A smaller dark spot, DS2, has also gone. Neptune has also increased in brightness with the advance of spring in the planet's southern hemisphere. The seasons each last over 40 years on Neptune.

The quetzal, the national bird of Guatemala, symbolizes freedom. The blue bands stand for the Caribbean Sea and the Pacific Ocean. The weapons represent the defence of liberty. Effective date: 15 September 1968. >>