"chance observation. In an 1846 letter to Wilhelm Struve, John Herschel states that he observed Neptune during a sweep of the sky on July 14, 1830. Although his telescope was powerful enough to resolve Neptune into a small blue disk and show it to be a planet, he did not recognize it at the time and mistook it for a star. In 1821, Alexis Bouvard had published astronomical tables of the orbit of Uranus, making predictions of future positions based on Newton's laws of motion and gravitation. Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize some"
"would only be as bright as magnitude −4.9, about the same as Venus despite its proximity. Judging by the color of its atmosphere, the sky of Neptune is probably an azure or sky blue, similar to Uranus'. As in the case of Uranus, it is unlikely that the planet's rings can be seen from its surface, as they are very thin and dark. Aside from the Sun, the most impressive object in Neptune's sky is its large moon Triton, which would appear slightly smaller than a full Moon on Earth. It moves more swiftly than our Moon, because of its"
"color of the planet Neptune reflects this. Its glyph is taken directly from Neptune's trident, symbolizing the curve of spirit being pierced by the cross of matter. Neptune takes 165 years to orbit the Sun, spending approximately 14 years (13.75) in each sign of the zodiac. Neptune was discovered in 1846. Astrologically speaking, Neptune is associated with idealism, dreams, dissolution, artistry, and empathy, but with illusion and vagueness too. Its appearance coincided with the discovery of anesthetics and hypnotism. In political terms, Neptune was linked to the rise of nationalist movements throughout Europe in countries like Germany, Italy, Hungary, Ireland,"
"mostly of water, methane, and ammonia. There is also some rock and gas, but various proportions of ice–rock–gas could mimic pure ice, so that the exact proportions are unknown. Uranus and Neptune have very hazy atmospheric layers with small amounts of methane, giving them aquamarine colors; light blue and ultramarine respectively. Both have magnetic fields that are sharply inclined to their axes of rotation. Unlike the other giant planets, Uranus has an extreme tilt that causes its seasons to be severely pronounced. The two planets also have other subtle but important differences. Uranus has more hydrogen and helium than Neptune"
"of two groupings has been speculated: These two groups are distinct (with 3σ confidence) in their distance from Uranus and in their eccentricity. However, these groupings are not directly supported by the observed colours: Caliban and Sycorax appear light red, whereas the smaller moons are grey. For Neptune, a possible common origin of Psamathe and Neso has been noted. Given the similar (grey) colours, it was also suggested that Halimede could be a fragment of Nereid. The two satellites have had a very high probability (41%) of collision over the age of the solar system. To date, the only irregular"
"to have caused it. Five new irregular moons discovered between 2002 and 2003 were announced in 2004. A new moon and the smallest yet, Neptune XIV, was found in 2013. Because Neptune was the Roman god of the sea, Neptune's moons have been named after lesser sea gods. Neptune has a planetary ring system, though one much less substantial than that of Saturn. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue. The three main rings are the narrow Adams Ring, 63,000 km from the centre of Neptune,"
"the dust fraction is 50%–100%, and are very different from the rings of Saturn and Uranus, which contain little dust (less than 0.1%). The particles in Neptune's rings are made from a dark material; probably a mixture of ice with radiation-processed organics. The rings are reddish in color, and their geometrical (0.05) and Bond (0.01–0.02) albedos are similar to those of the Uranian rings' particles and the inner Neptunian moons. The rings are generally optically thin (transparent); their normal optical depths do not exceed 0.1. As a whole, the Neptunian rings resemble those of Jupiter; both systems consist of faint,"
"a mass about 1.2 times that of Earth. The pressure at the centre is 7 Mbar (700 GPa), about twice as high as that at the centre of Earth, and the temperature may be 5,400 K. At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium. A trace amount of methane is also present. Prominent absorption bands of methane exist at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune's vivid azure"
"(but not as red as the colours of some Kuiper belt objects). Each planet's system displays slightly different characteristics. Jupiter's irregulars are grey to slightly red, consistent with C, P and D-type asteroids. Some groups of satellites are observed to display similar colours (see later sections). Saturn's irregulars are slightly redder than those of Jupiter. The large Uranian irregular satellites (Sycorax and Caliban) are light red, whereas the smaller Prospero and Setebos are grey, as are the Neptunian satellites Nereid and Halimede. With the current resolution, the visible and near-infrared spectra of most satellites appear featureless. So far, water ice"
"to the planet. Proteus is the second-largest moon of Neptune. It is about 420 kilometres in diameter, larger than Nereid, the second to be discovered. It was not discovered by Earth-based telescopes because it is so close to Neptune that it is lost in the glare of reflected sunlight. The surface of Proteus is dark—its geometrical albedo is about 10%. The color of its surface is neutral as the reflectivity does not change appreciably with the wavelength from violet to green. In the near-infrared around 2 μm Proteus's surface becomes less reflective, pointing to a possible presence of complex organic"
"(assuming an albedo of 0.04) and appears neutral (grey) in the visible light. Given the very similar colour of the satellite to that of Nereid together with the high probability (41%) of collision in the past lifespan of the Solar System, it has been suggested that the satellite could be a fragment of Nereid. Halimede, like many of the outer satellites of Neptune, is named after one of the Nereids, the fifty daughters of Nereus and Doris. Before the announcement of its name on February 3, 2007 (IAUC 8802), Halimede was known by the provisional designation S/2002 N 1. Halimede"
"20th century. The planet's distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by ""Voyager 2"", when it flew by the planet on 25 August 1989. The advent of the ""Hubble Space Telescope"" and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar. Like Jupiter and Saturn, Neptune's atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but it contains a higher proportion of ""ices"" such as water, ammonia, and methane. However, its interior, like"
"between 0.49 and 0.66. Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturn's moon Iapetus. The color varies between charcoal black, dark orange and white. Pluto's color is more similar to that of Io with slightly more orange, significantly less red than Mars. ""New Horizons"" found that Pluto's surface age is equally variable, with ancient, dark, mountainous terrain (such as Cthulhu) being found alongside the bright, flat, effectively craterless Sputnik Planitia and various terrains of intermediate age and color. Pluto's surface color has changed between 1994 and 2003: the northern polar"
"results from polarimetric studies indicate that the planet has predominately blue color, is 1.36 times as large and 0.74 times as massive as Jupiter, meaning that the mean density is 0.36g/cm. It has a geometric albedo of 0.35 in visible light. Tidal heating models predict a similar mass for the planet. Upsilon Andromedae b appears to be responsible for increased chromospheric activity on its parent star. Observations suggest that there is a ""hot spot"" on the star around 169° away from the sub-planetary point. This may be the result of interactions between the magnetic fields of the planet and the"
"light occur at irregular intervals; in the 50 years from 1947 to 1997, the spot was darkest in the periods 1961–1966, 1968–1975, 1989–1990, and 1992–1993. In November 2014, an analysis of data from NASA's Cassini mission revealed that the red color is likely a product of simple chemicals being broken apart by sunlight in the planet's upper atmosphere The Great Red Spot should not be confused with the Great Dark Spot, a feature observed near Jupiter's north pole in 2000 by the Cassini–Huygens spacecraft. A feature in the atmosphere of Neptune was also called the Great Dark Spot. The latter"
"Neptune Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of . It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the"
"that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered ""ice giants"" to emphasise this distinction. Traces of methane in the outermost regions in part account for the planet's blue appearance. In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has active and visible weather patterns. For example, 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. These weather patterns are driven by the strongest sustained winds of any planet"
"in size to Huya. Its surface is thought to have a pink tinge, resulting from chemical changes produced by the effect of radiation on frozen water, methane, and carbon dioxide. This optical color is consistent with formation in the gas-giant region and not the classical Kuiper belt, which is dominated by ultra-red colored objects. was first observed on 5 November 2012 with NOAO's 4-meter Víctor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Carnegie’s 6.5-meter Magellan telescope at Las Campanas Observatory in Chile was used to determine its orbit and surface properties. Before being announced to the public, it"
"a hazy brownish/dark orange color. As a consequence of its greater distance from the Sun and the opacity of its atmosphere, the surface of Titan receives only about of the sunlight Earth does – daytime on Titan is thus only as bright as twilight on the Earth. It seems likely that Saturn is permanently invisible behind orange smog, and even the Sun would only be a lighter patch in the haze, barely illuminating the surface of ice and methane lakes. However, in the upper atmosphere, the sky would have a blue color and Saturn would be visible. With its thick"
"an exoplanet was determined for the first time. The best-fit albedo measurements of HD 189733b suggest that it is deep dark blue. Later that same year, the colors of several other exoplanets were determined, including GJ 504 b which visually has a magenta color, and Kappa Andromedae b, which if seen up close would appear reddish in color. The apparent brightness (apparent magnitude) of a planet depends on how far away the observer is, how reflective the planet is (albedo), and how much light the planet receives from its star, which depends on how far the planet is from the"
"differs from Uranus's milder cyan. Because Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour. Neptune's atmosphere is subdivided into two main regions: the lower troposphere, where temperature decreases with altitude, and the stratosphere, where temperature increases with altitude. The boundary between the two, the tropopause, lies at a pressure of . The stratosphere then gives way to the thermosphere at a pressure lower than 10 to 10 bars (1 to 10 Pa). The thermosphere gradually transitions to the exosphere. Models suggest that Neptune's troposphere is banded by"
"NGC 3918 NGC 3918 is a bright planetary nebula in the constellation Centaurus, nicknamed the ""Blue Planetary"" or ""The Southerner"". It is the brightest of the far southern planetary nebulae. This nebula was discovered by Sir John Herschel in March 1834, and is easily visible through small telescopes. The round or even slightly oval diameter is telescopically between 8 and 10 arcsec, though deep images extends this to about 19 or 20 arcsec. More surprising is the beautiful rich blue colour that looks much like the coloured images of Neptune taken by Voyager 2 in 1989. Spectroscopy reveals NGC 3918"
"announced in 2005 appeared to show that Neptune's rings are much more unstable than previously thought. Images taken from the W. M. Keck Observatory in 2002 and 2003 show considerable decay in the rings when compared to images by ""Voyager 2"". In particular, it seems that the ""Liberté"" arc might disappear in as little as one century. Neptune brightened significantly between 1980 and 2000. The apparent magnitude currently ranges from 7.67 to 7.89 with a mean of 7.78 and a standard deviation of 0.06. Prior to 1980 the planet was as faint as magnitude 8.0. Neptune is too faint to"
"magnetic field. In the infrared part of the spectrum, Neptune's storms appear bright against the cooler background, allowing the size and shape of these features to be readily tracked. ""Voyager 2"" is the only spacecraft that has visited Neptune. The spacecraft closest approach to the planet occurred on 25 August 1989. Because this was the last major planet the spacecraft could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, similarly to what was done for ""Voyager 1""s encounter with Saturn and its moon Titan. The images relayed back"
"eye: its apparent magnitude is never brighter than 7.7. Therefore, the first observations of Neptune were only possible after the invention of the telescope. There is evidence that Neptune was seen and recorded by Galileo Galilei in 1613, Jérôme Lalande in 1795 and John Herschel in 1830, but none is known to have recognized it as a planet at the time. These pre-discovery observations were important in accurately determining the orbit of Neptune. Neptune would appear prominently even in early telescopes so other pre-discovery observation records are likely. Galileo's drawings show that he observed Neptune on December 28, 1612, and"
"dioxide and water, which may have been deposited from external sources such as meteorites and dust. Neptune resembles Uranus in its magnetosphere, with a magnetic field strongly tilted relative to its rotational axis at 47° and offset at least 0.55 radii, or about 13,500 km from the planet's physical centre. Before ""Voyager 2"" arrival at Neptune, it was hypothesised that Uranus's tilted magnetosphere was the result of its sideways rotation. In comparing the magnetic fields of the two planets, scientists now think the extreme orientation may be characteristic of flows in the planets' interiors. This field may be generated by"
"by Jupiter. Neptune's equatorial radius of 24,764 km is nearly four times that of Earth. Neptune, like Uranus, is an ice giant, a subclass of giant planet, because they are smaller and have higher concentrations of volatiles than Jupiter and Saturn. In the search for extrasolar planets, Neptune has been used as a metonym: discovered bodies of similar mass are often referred to as ""Neptunes"", just as scientists refer to various extrasolar bodies as ""Jupiters"". Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the"
"particles at wavelengths in the order 3 µm, which is in the near-infrared range, over Rayleigh scattering by gas molecules. Mars surface color The surface of the planet Mars appears reddish from a distance because of rusty dust suspended in the atmosphere. From closeup, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals. The apparent colour of the Martian surface enabled humans to distinguish it from other planets early in human history and motivated them to weave fables of war in association with Mars. One of its earliest recorded"
"Mars surface color The surface of the planet Mars appears reddish from a distance because of rusty dust suspended in the atmosphere. From closeup, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals. The apparent colour of the Martian surface enabled humans to distinguish it from other planets early in human history and motivated them to weave fables of war in association with Mars. One of its earliest recorded names, Har decher, literally meant ""Red One"" in Egyptian. Its color may have also contributed to a malignant association in"
"planet Neptune as perceived with the naked eye, which has an apparent magnitude of 7.78 at its brightest. The star's actual brightness is measured with an absolute magnitude of 4.12, similar to that of the Sun. HD 154672 b is a Hot Jupiter, as it is a closely orbiting planet with a high mass. Specifically, HD 154672 has a mass that is 5.02 times greater than Jupiter's mass. It also orbits at a distance of 0.6 AU, or about 60% of the mean distance between the Earth and Sun. This orbit is completed every 163.91 days. HD 154672 b has"
"is markedly different from minor planets of the outer solar system, centaurs Pholus, Chiron and Chariklo, suggesting that Nereid formed around Neptune rather than being a captured body. Halimede, which has similar colours, may be a fragment of Nereid that was broken off during a collision. The only spacecraft to visit Nereid was ""Voyager 2"", which passed it at a distance of between 20 April and 19 August 1989. ""Voyager 2"" obtained 83 images with observation accuracies of to . Prior to ""Voyager 2""'s arrival, observations of Nereid had been limited to ground-based observations that could only establish its intrinsic"
"and Serbia, seeking independence for their nations inspired by an idealized past of legend. It was also linked to the rise of socialism and the beginnings of the welfare state. Neptune coincided with the utopian ideals of Communism, when Marx and Engels first published 'The Communist Manifesto' in 1848. Neptune also represents the day of Friday, alongside Venus. In art, the impressionist movement began a trend away from literal representation, to one based on the subtle, changing moods of light and color. In medicine, Neptune is seen to be particularly associated with the thalamus, the spinal canal, and uncertain illnesses"
"been considered as a cause. The color of the markings, reddish-brown, is theorized to be caused by sulfur, but scientists cannot confirm that, because no data collection devices have been sent to Europa. Europa is primarily made of silicate rock and likely has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Ganymede (Jupiter III), the third Galilean moon is named after the mythological Ganymede, cupbearer of the Greek gods and Zeus's beloved. Ganymede is the largest natural satellite in the Solar System at 5262.4 kilometers in diameter, which makes it larger than the planet Mercury –"