Concept

Neptune

Overview

Neptune is the eighth and farthest known planet orbiting the Sun. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth. Compared to Uranus, its neighbouring ice giant, Neptune is slightly smaller, but more massive and dense. Being composed primarily of gases and liquids, it has no well-defined solid surface. Neptune orbits the Sun once every 164.8 years at an orbital distance of 30.1 astronomical units (4.5 billion kilometres; 2.8 billion miles). It is named after the Roman god of the sea and has the astronomical symbol , representing Neptune's trident.

Neptune is not visible to the unaided eye and is the only planet in the Solar System that was not initially observed by direct empirical observation. Rather, unexpected changes in the orbit of Uranus led Alexis Bouvard to hypothesise that its orbit was subject to gravitational perturbation by an unknown planet. After Bouvard's death, the position of Neptune was mathematically predicted from his observations, independently, by John Couch Adams and Urbain Le Verrier. Neptune was subsequently directly observed with a telescope on 23 September 1846 by Johann Gottfried Galle within a degree of the position predicted by Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining moons were located telescopically until the 20th century.

The planet's distance from Earth gives it a small apparent size, and its distance from the Sun renders it very dim, making it challenging to study with Earth-based telescopes. Only the advent of the Hubble Space Telescope and of large ground-based telescopes with adaptive optics allowed for detailed observations. Voyager 2, which flew by Neptune on 25 August 1989, remains the only spacecraft to visit the planet. Like the gas giants (Jupiter and Saturn), Neptune's atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but contains a higher proportion of ices such as water, ammonia and methane. Similar to Uranus, its interior is primarily composed of ices and rock; both planets are normally considered "ice giants" to distinguish them. Along with Rayleigh scattering, traces of methane in the outermost regions make Neptune appear faintly blue.

In contrast to the strongly seasonal atmosphere of Uranus, which can be featureless for long periods of time, Neptune's atmosphere has active and consistently visible weather patterns. At the time of the Voyager 2 flyby in 1989, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. In 2018, a newer main dark spot and smaller dark spot were identified and studied. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, as high as 2,100 km/h (580 m/s; 1,300 mph). Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K (−218 °C; −361 °F). Temperatures at the planet's centre are approximately 5,400 K (5,100 °C; 9,300 °F). Neptune has a faint and fragmented ring system (labelled "arcs"), discovered in 1984 and confirmed by Voyager 2.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

Possible passages

Found by search and not yet checked by a person; they may only mention the idea in passing.

1. For Neptune himself is called the Breeder. And the race of Hellen sacrificed to Neptune as the first father, imagining, as likewise the Syrians did, that man rose from a liquid substance. And therefore they worship a fish as of the same production and breeding with themselves, in this matter being more happy in their philosophy than Anaximander; for he says that fish and men were not produced in the…

   Plutarch, Complete Works of Plutarch — Volume 3

   States what Neptune is; names Neptune several times.

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2. Thus all things shook and cried, When this black battle of the Gods was joining. Thus array’d ‘Gainst Neptune, Phœbus with wing’d shafts; ’gainst Mars, the blue-ey’d Maid; ‘Gainst Juno, Phœbe, whose white hands bore singing darts of gold, Her side arm’d with a sheaf of shafts, and (by the birth twofold Of bright Latona) sister twin to Him that shoots so far.

   Homer, The Iliads of Homer Translated according to the Greek

   Names Neptune several times; opens on Neptune.

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3. Neptune engages on the part of the Grecians. The battle proceeds. Deiphobus advances to combat, but is repulsed by Meriones, who losing his spear, repairs to his tent for another. Teucer slays Imbrius, and Hector Amphimachus.

   Homer, The Iliad of Homer

   Names Neptune twice; opens on Neptune.

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Philosophers who discussed Neptune

• Karl Popper
• Philip Kitcher

Related ideas

• Greek language
• Urbain Le Verrier
• University of St Andrews
• The Guardian
• Meteorology
• Oxygen
• Planet
• Poseidon
• Greek mythology
• Sun
• Solar System
• Roman mythology
• Scientific American
• Galileo Galilei
• PBS
• The New York Times
• Indonesian language
• Gravity
• New Scientist
• Nature (journal)
• Uranus
• Thai language
• Māori language
• Cambridge University Press

Opposing perspectives

• Planet

Place in the tradition

Part of Confirmation holism.

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