Neptune and Moons - Astronomy Matters

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Neptune and Moons . . .

Neptune was the god of the sea in Roman mythology. He had power over the sea and seafaring. For example, he could cause--or prevent--storms at sea. Neptune resembled the Greek god Poseidon. Like Poseidon, he was also the god of earthquakes and horses.

The ancient Romans were a seafaring people and imported much of their food and other necessities by ship. As ruler of the sea, Neptune thus had an important role in their daily life. Sea travel was dangerous in ancient times, and Roman sailors prayed to Neptune for safe voyages. After their return, sailors often showed their gratitude by dedicating a valuable object to Neptune.

Neptune was the son of Saturn and Ops (called Cronus and Rhea by the Greeks). He married the sea nymph Amphitrite, and they had a son, Triton, who was half man and half fish. Triton played an important role in many ancient legends about the sea.

Neptune is one of the two planets that cannot be seen without a telescope. The other is Pluto. Neptune is about 30 times as far from the sun as is Earth. Pluto is the only planet farther from the sun than Neptune. But every 248 years Pluto moves inside Neptune's orbit for about a 20-year period, during which it is closer to the sun than Neptune. Pluto last crossed Neptune's orbit on Jan. 23, 1979, and remained within it until Feb. 11, 1999.

Neptune's diameter at the equator is 30,775 miles (49,528 kilometers), or almost 4 times that of Earth. It is about 17 times as massive (heavy) as Earth, but is not so dense as Earth. Neptune has eight satellites (moons) and several rings around it.

Neptune travels around the sun in an elliptical (oval-shaped) orbit. Its average distance from the sun is about 2,793,100 miles (4,495,060,000 kilometers). Neptune goes around the sun once about every 165 Earth years, compared with once a year for Earth. As Neptune orbits the sun, it spins on its axis, an imaginary line through its center. Neptune's axis is not perpendicular (at an angle of 90°) to the planet's path around the sun. The axis tilts about 28° from the perpendicular position. Neptune spins around once in about 16 hours and 7 minutes.