Named for the Roman god of the sea, the brother of Jupiter, Neptune is the most remote of the jumbo gas planets in the Solar System. It is the eighth planet out from the Sun among the nine known planets.
Neptune averages some 2,794,000,000 miles from the Sun. The length of its year is about 165 Earth years for one trip around the Sun. Neptune's orbit is even more nearly circular than Earth's. It has an 18 hour day plus-or-minus 24 minutes.
Big but faint. Neptune's diameter at the equator is about 31,000 miles. Neptune's mass is about 17 times Earth, slightly smaller and heavier than Uranus, with an internal structure similar to Uranus. The planet's atmosphere is mostly hydrogen, methane, and ammonia, similar to Uranus, except for a warmer stratosphere. The planet's density is 1.67 (water is 1).
For Earth astronomers, Neptune reaches a brightness of magnitude 7.8, five times too faint to see with the naked eye. It looks like a small blue-green disk when seen through a large telescope.
Solar System: The Sun Inner System: Mercury Venus Earth Mars Outer System: Jupiter Saturn Uranus Neptune Pluto Other Bodies: Moons Rings Asteroids Comets
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