Neptune is the eighth and farthest known planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Among the giant planets in the Solar System, Neptune is the most dense. Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 astronomical units (4.50×109 km). Neptune has 14 known moons. Triton is the largest Neptunian moon, comprising more than 99.5% of the mass in orbit around Neptune, and it is the only one massive enough to be spheroidal. Named after the Roman god of the sea, its astronomical symbol is ♆, a stylised version of the god Neptune's trident.
Poseidon (Greek: Ποσειδῶν) was one of the twelve Olympian deities of the pantheon in Greek mythology. His main domain was the ocean, and he is called the "God of the Sea". Neptune was the god of freshwater and the sea in Roman religion. He is the counterpart of the Greek god Poseidon.