Plaja Neptun

Neptune is the eighth planet from the Sun in the Solar System. Named after the Roman god of the sea, Neptune, it is the fourth-largest planet by diameter and the third-largest by mass. Neptune has a mass 17 times greater than that of Earth and slightly greater than that of Uranus, which is 15 times heavier than Earth but not as dense. Neptune orbits the Sun at a distance of 30.1 astronomical units, meaning its orbit is about 30 times larger than Earth's orbit. Neptune's astronomical symbol is ♆, a modified variant of the trident of the god Neptune.

Neptune was the first planet found through mathematical calculations. The planet Neptune was discovered because of gravitational perturbations in the orbit of Uranus, which led Alexis Bouvard to hypothesize the existence of an eighth planet. Neptune was subsequently observed on 23 September 1846 by Johann Galle, less than one degree from the position predicted by Urbain Le Verrier's calculations. Shortly afterwards its moon Triton was also discovered. Another 12 moons were discovered during the 20th century. On 25 August 1989, the Voyager 2 spacecraft passed through the planet's vicinity.

Neptune has a composition similar to that of Uranus, and the compositions of both planets differ from those of the larger gas giants, Jupiter and Saturn. Neptune's atmosphere is similar to that of Jupiter and Saturn in that it is composed mainly of hydrogen, helium, traces of hydrocarbons and possibly nitrogen, but it has higher proportions of water, ammonia and methane. Astronomers sometimes classify Neptune and Uranus as "ice giants" in order to emphasize these distinctions. Neptune's interior, as with Uranus, is composed mainly of rock and ice. The traces of methane in the upper layers of the atmosphere largely give the planet its bluish appearance.

Unlike the uniform atmosphere of Uranus, Neptune has an atmosphere with visible features that indicate meteorological activity. For example, in 1989, when Voyager 2 reached Neptune, a large dark spot was observed, similar to the Great Red Spot on Jupiter. These weather phenomena are produced by the strongest winds in the Solar System, whose speeds reach, according to measurements, 2100 km/h. Also, because Neptune is far from the Sun, it has one of the coldest atmospheres in the Solar System, with the temperatures of the upper cloud layers reaching -218 °C (55 K). The temperature of its core is about 5000 °C. Neptune has a system of two rings that are, however, hard to observe and fragmented; the existence of the rings was suggested by analyses of photographs of the planet from 1968, but definitive confirmation was made only in 1989 by the Voyager 2 probe.