Neptune is eighth planet in the Solar System and is located farthest from the Sun, at a distance of 2.793 billion miles. It is the fourth biggest planet in the Solar System in terms of diameter, the third most massive, and is regarded as the densest giant planet. Neptune is approximately 17 times largest than Earth in terms of mass, and orbits the Sun once every 165 years. It is the only planet in the Solar System that cannot be seen from Earth by the naked eye, as well as the only planet that was first found by mathematical prediction rather than empirical observation.
Discovery of Neptune
Neptune is the outermost planet in the Solar System and was discovered on September 23, 1846 at the Berlin Observatory by German astronomer Johann Gottfriend Galle, based on the predictions by French astronomer Urbain Le Verrier. The discovery came as a result of analyzing data related to the orbit of the planet Uranus. According to astronomers, there was a discrepancy between the observed orbit of Uranus and the mathematical predictions of its position. As a result, it was suspected that a nearby planet was causing the discrepancy due to gravitational interaction. British astronomer John Couch Adams and Urbain Le Verrier began to independently develop mathematical predictions of the new planet in 1843 and 1845, respectively, but Neptune was not actually observed until 1846 by Galle, who found the planet to be within a degree of its predicted position. Additionally, historical records suggest that Italian astronomer Galileo Galilei may have have observed Neptune through one of his earliest telescopes in 1612, but mistook the planet for a fixed star.
Upon its discovery, Neptune was simply known as "the planet exterior to Uranus." Galle proposed the name Janus, while British astronomer James Challis suggested the planet be named Oceanus. Le Verrier claimed he had the right to name the planet, as it was discovered based on his predictions. He suggested the name Neptune, and falsely claimed that the name had already been approved by the French Bureau des Longitudes. Le Verrier later attempted to name the planet after himself, but the suggestion was resisted outside France. On December 29th, 1846, German-Russian astronomer Friedrich Georg Wilhelm von Struve supported the name Neptune to the Saint Petersburg Academy of Sciences. Neptune was quickly accepted internationally as the name of the new planet. In Roman mythology, Neptune was the god of the sea, and was equivalent to Poseidon in Greek mythology. The use of a mythological name for the planet gained support because all other planets, except Earth, had been named after Roman and Greek gods. Other languages typically use a variant of name Neptune. For example, in the Korean, Japanese, Vietnamese, and Chinese languages, the planet's name translates to "sea king star."
Neptune has 14 identified moons. Triton is the largest of Neptune's moons and accounts for more than 99.5% of all mass in orbit around the planet. The moon was discovered about two weeks after the planet, and unlike the other moons of Neptune, Triton has been observed to have a retrograde orbit, implying that it may have been a dwarf planet captured from the Kuiper belt. Triton has been observed to spiral gradually inward as a result of tidal acceleration, and astronomers believe that the moon will eventually be torn apart when it reaches the Roche limit, which will occur in an estimated 3.6 billion years.