Neptune (astronomy)


May 25, 2022

Neptune is the eighth and farthest planet in the Solar System from the Sun. It is the fourth largest planet, considering its diameter, and the third largest when considering its mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, whose mass equals 15 Earth masses, but is less dense than Neptune. The name of the planet is dedicated to the Roman god of the sea (Neptune); its symbol is ♆ (), a stylized version of Neptune's trident. Discovered on the evening of 23 September 1846 by Johann Gottfried Galle with the telescope of the Berlin Astronomical Observatory, and Heinrich Louis d'Arrest, an astronomy student who assisted him, Neptune was the first planet to have been found through mathematical calculations more than through regular observations: unusual changes in Uranus' orbit led astronomers to believe that there was an unknown planet outside that disturbed its orbit. The planet was discovered within just one degree of the predicted point. The moon Triton was identified shortly thereafter, but none of Neptune's thirteen other natural satellites were discovered before the 20th century. The planet was visited by only one space probe, the Voyager 2 which passed close to it on August 25, 1989. Neptune is similar in composition to Uranus and both have different compositions from those of the larger gas planets Jupiter and Saturn. For this they are sometimes classified in a separate category, the so-called "ice giants". The atmosphere of Neptune, although similar to those of both Jupiter and Saturn being composed mainly of hydrogen and helium, also has greater proportions of "ices", such as water, ammonia and methane, along with traces of hydrocarbons and perhaps nitrogen. In contrast, the planet's interior is essentially made up of ice and rocks like its fellow Uranus. Traces of methane present in the outermost layers of the atmosphere help give the planet Neptune its distinctive deep blue color. Neptune has the strongest winds of any other planet in the Solar System. Gusts were measured at speeds above 2100 km / h. At the time of the flyover by Voyager 2, in 1989, the southern hemisphere of the planet possessed a Great Dark Spot similar to the Great Red Spot of Jupiter; the temperature of the highest clouds of Neptune was about −218 ° C, one of the coldest in the Solar System, due to the great distance from the Sun. The temperature in the center of the planet is about 7000 ° C, comparable with the surface temperature of the Sun and similar to that of the nucleus of many other known planets. The planet also has a weak ring system, discovered in the 1960s but only confirmed by Voyager 2.


Neptune is invisible to the naked eye from Earth; its apparent magnitude, always between 7.7 and 8.0, requires at least binoculars to allow for the identification of the planet. Seen through a large telescope, Neptune appears as a small bluish disk with an apparent diameter of 2, 2–2.4 seconds of arc similar in appearance to Uranus. The color is due to the presence of methane in the Neptunian atmosphere, at a rate of 2%. There has been a marked improvement in the visual study of the planet from Earth with the advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics. The best images obtainable from Earth today allow us to identify its most pronounced cloud formations and polar regions, which are lighter than the rest of the atmosphere. With less precise instruments it is impossible to locate any surface formation on the planet, and it is preferable to devote oneself to the search for its main satellite, Triton. At observations in radio frequencies, Neptune appears to be the source of two emissions: one continuous and rather weak, the other irregular and