Neptune is the eighth planet from the sun and the fourth largest in the solar system. It is one of the two giant ice planets. It was name after the ancient Roman god of the sea, Neptune. The Greeks called him Poseidon. Its astronomical symbol is the trident.
The atmosphere consists primarily of hydrogen and helium. There are proportionately larger amounts of frozen water, methane,and ammonia in the atmosphere than in the atmospheres of Jupiter and Saturn.
The planet orbits the sun once every 164.8 years or 60,182 days. A Neptunian year lasts 89,666 Neptunian days. It reaches its most distant point from the sun at about 2.84 billion miles (4.54 billion kilometers). It reaches its closest point to the sun at about 2.79 billion miles (4.46 billion kilometers). It makes a complete rotation on its axis every 16 hours 6 minutes 36 seconds.
It has 14 moons and a magnetosphere. The largest moon is Triton. Like Saturn and Uranus, Neptune has a ring system, but the rings are substantially thinner than the ones around Saturn. The planet radiates 2.61 times more energy than it receives from the sun.
Surface temperatures may range from -360 ºF (-218 ºC) to -330 ºF ( -201 ºC). The surface gravity is 1.14 times that of Earth's.
Neptune is not visible to the naked eye. A telescope is needed in order to see it. The planet was discovered by mathematical prediction. Johann Galle is the first person to observe the planet. He saw it for the first time on Septermber 23, 1846 using a telescope.
