Uranus  

Uranus, as seen by Voyager 2
Discovery
Discovered by	William Herschel
Discovery date	March 13, 1781
Orbital characteristics[1][2]
Epoch J2000
Aphelion	3,004,419,704 km 20.08330526 AU
Perihelion	2,748,938,461 km 18.37551863 AU
Semi-major axis	2,876,679,082 km 19.22941195 AU
Eccentricity	0.044405586
Orbital period	30,799.095 days 84.323326 yr
Synodic period	369.66 days[3]
Average orbital speed	6.81 km/s[3]
Mean anomaly	142.955717°
Inclination	0.772556° 6.48° to Sun's equator
Longitude of ascending node	73.989821°
Argument of perihelion	96.541318°
Satellites	27
Physical characteristics
Equatorial radius	25,559 ± 4 km 4.007 Earths[4][5]
Polar radius	24,973 ± 20 km 3.929 Earths[4][5]
Flattening	0.0229 ± 0.0008
Surface area	8.1156×109 km²[6][5] 15.91 Earths
Volume	6.833×1013 km³[3][5] 63.086 Earths
Mass	8.6810 ± 13×1025 kg 14.536 Earths[7] GM=5,793,939 ± 13 km³/s²
Mean density	1.27 g/cm³[3][5]
Equatorial surface gravity	8.69 m/s²[3][5] 0.886 g
Escape velocity	21.3 km/s[3][5]
Sidereal rotation period	−0.71833 day 17 h 14 min 24 s[4]
Equatorial rotation velocity	2.59 km/s 9,320 km/h
Axial tilt	97.77°[4]
North pole right ascension	17 h 9 min 15 s 257.311°[4]
North pole declination	−15.175°[4]
Albedo	0.300 (bond) 0.51 (geom.)[3]
Surface temp.    1 bar level[9]    0.1 bar (tropopause)[10]	min mean max 76 K 49 K 53 K 57 K
Apparent magnitude	5.9[8] to 5.32[3]
Angular diameter	3.3"–4.1"[3]
Adjectives	Uranian
Atmosphere[10][11][12][13]
Scale height	27.7 km[3]
Composition	(Below 1.3 bar) 83±3% Hydrogen (H2) 15±3% Helium 2.3% Methane 0.009% (0.007-0.015%) Hydrogen deuteride (HD)[14] Ices: Ammonia water ammonium hydrosulfide (NH4SH) methane (CH4)

Uranus (pronounced /ˈjʊərənəs/ or /jʊˈreɪnəs/^[15]) is the seventh planet from the Sun and the third-largest and fourth-most massive planet in the solar system. It is named after the ancient Greek deity of the sky (Uranus, Οὐρανός), the father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Uranus was the first planet discovered in modern times. Though it is visible to the naked eye like the five classical planets, it was never recognized as a planet by ancient observers due to its dimness.^[16] Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the solar system for the first time in modern history. This was also the first discovery of a planet made using a telescope. Uranus can refer to: Uranus, the seventh planet from the Sun Uranus (astrology) astrological aspects of Uranus Uranus (mythology), a deity in Greek mythology Sailor Uranus, from the popular media franchise Sailor Moon Uranus (1990 movie) Uranus is used euphemistically and humorously as a pun, as it can be pronounced... Image File history File links Uranus_symbol. ... Image File history File linksMetadata Download high-resolution version (1724x1716, 89 KB) A photo of Uranus taken by Voyager 2. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... For other persons named William Herschel, see William Herschel (disambiguation). ... is the 72nd day of the year (73rd in leap years) in the Gregorian calendar. ... 1781 was a common year starting on Monday (see link for calendar). ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... The J2000. ... A diagram of Keplerian orbital elements. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... The astronomical unit (AU or au or a. ... A diagram of Keplerian orbital elements. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Look up day in Wiktionary, the free dictionary. ... In astronomy, a Julian year is a unit of time defined as exactly 365. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. ... For the science fiction novella by William Shunn, see Inclination (novella). ... Sol redirects here. ... The Longitude of the ascending node (☊, also noted Ω) is one of the orbital elements used to specify the orbit of an object in space. ... The argument of periapsis (ω) is the orbital element describing the angle between an orbiting bodys ascending node (the point where the body crosses the plane of reference from South to North) and its periapsis (the point of closest approach to the central body), measured in the orbital plane and... A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. ... Uranus has 27 known moons. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... A geographical pole is either of two fixed points on the surface of a spinning body or planet, at 90 degrees from the equator, based on the axis around which a body spins. ... 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For other uses, see Albedo (disambiguation). ... The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space. ... The geometric albedo of an astronomical body is the ratio of its total brightness at zero phase angle to that of an idealised fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. ... For other uses, see Temperature (disambiguation). ... The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... The tropopause is between the troposphere and the stratosphere. ... For other uses, see Kelvin (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... 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This article is about the astronomical term. ... Sol redirects here. ... This article is about the Solar System. ... For other uses, see Uranus (disambiguation). ... Cronus is not to be confused with Chronos, the personification of time. ... Saturnus, Caravaggio, 16th c. ... For other uses, see Zeus (disambiguation). ... For the planet see Jupiter. ... The term Modern Times is used by historians to loosely describe the period of time immediately following what is known as the Early Modern Times. ... The final definition left the solar system with eight planets, pictured above (not to scale). ... For other persons named William Herschel, see William Herschel (disambiguation). ... is the 72nd day of the year (73rd in leap years) in the Gregorian calendar. ... 1781 was a common year starting on Monday (see link for calendar). ... This article is about the Solar System. ... This article does not cite any references or sources. ...

Uranus and Neptune have internal and atmospheric compositions different from those of the larger gas giants Jupiter and Saturn. As such, astronomers sometimes place them in a separate category, the "ice giants". Uranus' atmosphere, while similar to Jupiter and Saturn in being composed primarily of hydrogen and helium, contains a higher proportion of "ices" such as water, ammonia and methane, along with the usual traces of hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds.^[10] For other uses, see Neptune (disambiguation). ... Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earths atmosphere and that of other planets is studied. ... This article does not cite any references or sources. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... From top: Neptune, Uranus, Saturn, and Jupiter. ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... For other uses, see Ammonia (disambiguation). ... Methane is a chemical compound with the molecular formula . ... Look up Hydrocarbon in Wiktionary, the free dictionary. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Cloud (disambiguation). ...

Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun; its north and south poles lie where most other planets have their equators.^[17] Seen from Earth, Uranus' rings can appear to circle the planet like an archery target and its moons revolve around it like the hands of a clock, though in 2007 and 2008 the rings appear edge-on. In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants.^[17] However, terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second.^[18] A planetary ring is a ring of dust and other small particles orbiting around a planet in a flat disc-shaped region. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. ... The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ... Modern competitive archery is governed by the International Archery Federation, abbreviated FITA (Fédération Internationale de Tir à lArc). ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... Categories: Stub ... This article or section is in need of attention from an expert on the subject. ... For the geological process, see Weathering or Erosion. ... For other uses, see Equinox (disambiguation). ... For other uses, see Wind (disambiguation). ...

Discovery

Uranus had been observed on many occasions prior to its discovery as a planet, but it was generally mistaken for a star. The earliest recorded sighting was in 1690 when John Flamsteed catalogued Uranus as 34 Tauri and observed it at least six times. The French astronomer, Pierre Lemonnier, observed Uranus at least twelve times between 1750 and 1769,^[19] including on four consecutive nights. John Flamsteed - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... Taurus (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac. ... Pierre Charles Le Monnier (November 23, 1715 – May 31, 1799) was a French astronomer. ...

Sir William Herschel observed the planet on 13 March 1781 while in the garden of his house at 19 New King Street in the town of Bath, Somerset (now the Herschel Museum of Astronomy),^[20] but initially reported it (on 26 April 1781) as a "comet".^[21] Herschel "engaged in a series of observations on the parallax of the fixed stars",^[22] using a telescope of his own design. For other persons named William Herschel, see William Herschel (disambiguation). ... is the 72nd day of the year (73rd in leap years) in the Gregorian calendar. ... 1781 was a common year starting on Monday (see link for calendar). ... , Bath is a small city in Somerset, England most famous for its historic baths fed by three hot springs. ... This article is about the county of Somerset in England. ... , The Herschel Museum of Astronomy (also known as the William Herschel Museum) is a small independent museum dedicated to the life and works of the famous astronomer, William Herschel and his sister, Caroline Herschel. ... is the 116th day of the year (117th in leap years) in the Gregorian calendar. ... 1781 was a common year starting on Monday (see link for calendar). ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ...

He recorded in his journal "In the quartile near ζ Tauri … either [a] Nebulous star or perhaps a comet".^[23] On March 17, he noted, "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place".^[24] When he presented his discovery to the Royal Society, he continued to assert that he had found a comet while also implicitly comparing it to a planet:^[25] is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... For other uses, see Royal Society (disambiguation). ...

Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from him on April 23: "I don't know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it".^[26] Astronomer Royal is a senior post in the Royal Household of the Sovereign of the United Kingdom. ... Nevil Maskelyne. ... is the 113th day of the year (114th in leap years) in the Gregorian calendar. ...

While Herschel continued to cautiously describe his new object as a comet, other astronomers had already begun to suspect otherwise. Russian astronomer Anders Johan Lexell estimated its distance as 18 times the distance of the Sun from the Earth, and no comet had yet been observed with a perihelion of even four times the Earth–Sun distance.^[27] Berlin astronomer Johann Elert Bode described Herschel's discovery as "a moving star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn".^[28] Bode concluded that its near-circular orbit was more like a planet than a comet.^[29] Anders Johan Lexell (December 24, 1740 – December 11, 1784 (Julian calendar: November 30)) was a Swedish_Russian astronomer and mathematician. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... Johann Elert Bode Johann Elert Bode (January 19, 1747 – November 23, 1826) was a German astronomer known for his contribution to the Titius-Bode law and his works to determine the orbit of Uranus, for which he also suggested the name. ...

The object was soon universally accepted as a new planet. By 1783, Herschel himself acknowledged this fact to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honour of pointing out to them in March 1781, is a Primary Planet of our Solar System."^[30] In recognition of his achievement, King George III gave Herschel an annual stipend of £200 on the condition that he move to Windsor so the Royal Family could have a chance to look through his telescopes.^[31] For clothing store, see JoS. A. Bank Clothiers. ... George III redirects here. ...

Naming

Maskelyne asked Herschel to "do the astronomical world the faver [sic] to give a name to your planet, which is entirely your own, & which we are so much obliged to you for the discovery of."^[32] In response to Maskelyne's request, Herschel decided to name the object Georgium Sidus (George's Star), or the "Georgian Planet" in honour of his new patron, King George III.^[33] He explained this decision in a letter to Joseph Banks:^[30]

William Herschel, discoverer of Uranus

Astronomer Jérôme Lalande proposed the planet be named Herschel in honour of its discoverer.^[34] Bode, however, opted for Uranus, the Latinized version of the Greek god of the sky, Ouranos. Bode argued that just as Saturn was the father of Jupiter, the new planet should be named after the father of Saturn.^[31][35][36] The earliest citation of the name Uranus in an official publication is in 1823, a year after Herschel's death.^[37][38] The name Georgium Sidus or "the Georgian" was still used infrequently (by the British alone) for some time thereafter; the final holdout was HM Nautical Almanac Office, which did not switch to Uranus until 1850.^[35] Image File history File linksMetadata William_Herschel01. ... Image File history File linksMetadata William_Herschel01. ... Joseph Jérôme Lefrançais de Lalande (July 11, 1732 – April 4, 1807) was a French astronomer. ... The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... For other uses, see Uranus (disambiguation). ... Her Majestys Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Greenwich Observatory (RGO), where the Nautical Almanac had been published since 1767. ...

The preferred pronunciation of the name Uranus among astronomers is [ˈjʊərənəs], with the first syllable stressed and a short a (ūrănŭs);^[39] this is more classically correct than the alternate [jʊˈɹeɪ.nəs], with stress on the second syllable and a "long a" (ūrānŭs), which is often used in the English-speaking world. For the computer operating system, see Syllable (operating system). ...

Uranus is the only planet whose name is derived from a figure from Greek mythology rather than Roman mythology. (The Roman equivalent would have been Caelus.) The adjective of Uranus is "Uranian". The element uranium, discovered in 1789, was named in its honour by its discoverer, Martin Klaproth.^[40] The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... A head of Minerva found in the ruins of the Roman baths in Bath Roman mythology, the mythological beliefs of the people of Ancient Rome, can be considered as having two parts. ... Caelus was the Latin name that the Romans used for the Greek sky god Uranus. ... This article is about the chemical element. ... Martin Heinrich Klaproth (December 1, 1743 – January 1, 1817) was a German chemist. ...

Its astronomical symbol is . It is a hybrid of the symbols for Mars and the Sun because Uranus was the Sky in Greek mythology, which was thought to be dominated by the combined powers of the Sun and Mars.^[41] Its astrological symbol is , suggested by Lalande in 1784. In a letter to Herschel, Lalande described it as "un globe surmonté par la première lettre de votre nom" ("a globe surmounted by the first letter of your name").^[34] In the Chinese, Japanese, Korean, and Vietnamese languages, the planet's name is literally translated as the sky king star (天王星).^[42][43] Chinese Celestial symbols on an antique bronze mirror Astronomical symbols are symbols used to represent various celestial objects, theoretical constructs and observational events. ... Image File history File links Uranus_symbol. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Sol redirects here. ... ... Image File history File links Uranus's_astrological_symbol. ...

Orbit and rotation

HST image of Uranus showing cloud bands, rings, and moons

Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU). The intensity of sunlight on Uranus is about 1/400 that of Earth.^[44] Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace.^[27] With time, discrepancies began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus' orbit. On September 23, 1846, Johann Gottfried Galle located a new planet, later named Neptune, at nearly the position predicted by Le Verrier.^[45] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... Billion may mean: 1,000,000,000 (one thousand million; ), used by most English-speaking countries (American and usual modern British meaning) 1,000,000,000,000 (one million million; ), used by most other countries outside Asia (older British meaning). ... The astronomical unit (AU or au or a. ... Pierre-Simon, marquis de Laplace (March 23, 1749 - March 5, 1827) was a French mathematician and astronomer whose work was pivotal to the development of mathematical astronomy. ... John Couch Adams (June 5, 1819 – January 21, 1892), was a British mathematician and astronomer. ... Urbain Le Verrier. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... 1846 was a common year starting on Thursday (see link for calendar). ... Johann Gottfried Galle Johann Gottfried Galle (June 9, 1812 in Radis, Saxony-Anhalt – July 10, 1910 in Potsdam, Brandenburg) was a German astronomer at the Berlin Observatory who, with the assistance of student Heinrich Louis dArrest, was the first person to view the planet Neptune, and know what he... For other uses, see Neptune (disambiguation). ...

The rotational period of the interior of Uranus is 17 hours, 14 minutes. However, as on all giant planets, its upper atmosphere experiences very strong winds in the direction of rotation. In effect, at some latitudes, such as about two-thirds of the way from the equator to the south pole, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.^[46]

Axial tilt

Uranus' axis of rotation lies on its side with respect to the plane of the solar system, with an axial tilt of 98 degrees. This makes its exchange of seasons completely unlike those of the other major planets. Other planets can be visualized to rotate like tilted spinning tops relative to the plane of the solar system, while Uranus rotates more like a tilted rolling ball. Near the time of Uranian solstices, one pole faces the Sun continually while the other pole faces away. Only a narrow strip around the equator experiences a rapid day-night cycle, but with the Sun very low over the horizon as in the Earth's polar regions. At the other side of Uranus' orbit the orientation of the poles towards the Sun is reversed. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.^[47] Near the time of the equinoxes, the Sun faces the equator of Uranus giving a period of day-night cycles similar to those seen on most of the other planets. Uranus reached its most recent equinox on 7 December 2007.^[48][49] For other uses, see Top (disambiguation). ... For other uses, see Ball (disambiguation). ... “Summer solstice” redirects here. ... Sol redirects here. ... For other uses, see Equinox (disambiguation). ... is the 341st day of the year (342nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ...

One result of this axis orientation is that, on average during the year, the polar regions of Uranus receive a greater energy input from the Sun than its equatorial regions. Nevertheless, Uranus is hotter at its equator than at its poles. The underlying mechanism which causes this is unknown. The reason for Uranus' unusual axial tilt is also not known with certainty, but the usual speculation is that during the formation of the Solar System, an Earth sized protoplanet collided with Uranus, causing the skewed orientation.^[50] Uranus' south pole was pointed almost directly at the Sun at the time of Voyager 2's flyby in 1986. The labeling of this pole as "south" uses the definition currently endorsed by the International Astronomical Union, namely that the north pole of a planet or satellite shall be the pole which points above the invariable plane of the solar system, regardless of the direction the planet is spinning.^[51][52] However, a different convention is sometimes used, where a body's north and south poles are defined according to the right-hand rule in relation to the direction of rotation.^[53] In terms of this latter coordinate system it was Uranus' north pole which was in sunlight in 1986. Astronomer Patrick Moore, commenting on the issue, summed it up by saying "Take your pick!"^[54] Protoplanets are moon-sized planet embryos within protoplanetary discs. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... IAU redirects here. ... The left-handed orientation is shown on the left, and the right-handed on the right. ... For other persons named Patrick Moore, see Patrick Moore (disambiguation). ...

Visibility

From 1995 to 2006, Uranus' apparent magnitude fluctuated between +5.6 and +5.9, placing it just within the limit of naked eye visibility at +6.5.^[8] Its angular diameter is between 3.4 and 3.7 arcseconds, compared with 16 to 20 arcseconds for Saturn and 32 to 45 arcseconds for Jupiter.^[8] At opposition, Uranus is visible to the naked eye in dark, un-light polluted skies, and becomes an easy target even in urban conditions with binoculars.^[6] In larger amateur telescopes with an objective diameter of between 15 and 23 cm, the planet appears as a pale cyan disk with distinct limb darkening. With a large telescope of 25 cm or wider, cloud patterns, as well as some of the larger satellites, such as Titania and Oberon, may be visible.^[55] The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars. ... This article is about the planet. ... For other uses, see Jupiter (disambiguation). ... This time exposure photo of New York City shows sky glow, one form of light pollution. ... The limb darkened Sun - An image of the Sun in visible light showing the limb darkening effect as a drop in intensity towards the edge or limb of the solar disk. ... Not to be confused with the Saturnian moon Titan or the asteroid 593 Titania. ... Atmospheric pressure 0 kPa Oberon (oe-bur-on) is the outermost of the major moons of the planet Uranus. ...

Physical characteristics

Internal structure

Size comparison of Earth and Uranus

Uranus' mass is roughly 14.5 times that of the Earth, making it the least massive of the giant planets, while its density of 1.27 g/cm³ makes it the second least dense planet, after Saturn.^[7] Though having a diameter similar to Neptune (roughly four times Earth's), it is less massive.^[4] These values indicate that it is made primarily of various ices, such as water, ammonia, and methane.^[9] The total mass of ice in Uranus' interior is not precisely known, as different figures emerge depending on the model chosen; however, it must be between 9.3 and 13.5 Earth masses.^[9][56] Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses.^[9] The remainder of the mass (0.5 to 3.7 Earth masses) is accounted for by rocky material.^[9] Image File history File linksMetadata Download high resolution version (900x900, 146 KB)Sources: Image:The Earth seen from Apollo 17. ... Image File history File linksMetadata Download high resolution version (900x900, 146 KB)Sources: Image:The Earth seen from Apollo 17. ... Volatiles are that group of compounds with low boiling points (see volatile) that are associated with a planets or moons crust and/or atmosphere. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... For other uses, see Ammonia (disambiguation). ... Methane is a chemical compound with the molecular formula . ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... This article is about the geological substance. ...

The standard model of Uranus' structure is that it consists of three layers: a rocky core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope.^[9][57] The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20 percent Uranus'; the mantle comprises the bulk of the planet, with around 13.4 Earth masses, while the upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and extending for the last 20 percent of Uranus' radius.^[9][57] Uranus' core density is around 9 g/cm³, with a pressure at the core/mantle boundary of 8 million bars (800 GPa) and a temperature of about 5000 K.^[56][57] The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, ammonia and other volatiles.^[9][57] This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean.^[58] The bulk compositions of Uranus and Neptune are very different from those of Jupiter and Saturn, with ice dominating over gases, hence justifying their separate classification as ice giants. Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... This article is about the chemistry of hydrogen. ... General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... For other uses, see Density (disambiguation). ... This article is about pressure in the physical sciences. ... The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... The gigapascal, symbol GPa is an SI unit of pressure. ... For other uses, see Kelvin (disambiguation). ... For other uses, see Ammonia (disambiguation). ... Volatiles are that group of compounds with low boiling points (see volatile) that are associated with a planets or moons crust and/or atmosphere. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... From top: Neptune, Uranus, Saturn, and Jupiter. ...

While the model considered above is more or less standard, it is not unique; other models also satisfy observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in the ice mantle, the total mass of ices in the interior will be lower, and, correspondingly, the total mass of rocks and hydrogen will be higher. Presently available data does not allow us to determine which model is correct.^[56] The fluid interior structure of Uranus means that it has no solid surface. The gaseous atmosphere gradually transitions into the internal liquid layers.^[9] However for the sake of convenience an oblate spheroid of revolution, where pressure equals 1 bar (100 kPa), is designated conditionally as a ‘surface’. It has equatorial and polar radii of 25,559 ± 4 and 24,973 ± 20 km, respectively.^[4] This surface will be used throughout this article as a zero point for altitudes. A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... This box:      For other uses, see Solid (disambiguation). ... An open surface with X-, Y-, and Z-contours shown. ... Oblate also refers to a member of the Roman Catholic religious order of the Missionary Oblates of Mary Immaculate, or in some cases to a lay or religious person who has officially associated himself (or herself) with a monastic community such as the Benedictines for reasons of personal enrichment without... The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... A geographical pole is either of two fixed points on the surface of a spinning body or planet, at 90 degrees from the equator, based on the axis around which a body spins. ... Altitude is the elevation of an object from a known level or datum. ...

Internal heat

Uranus' internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux.^[59][18] Why Uranus' internal temperature is so low is still not understood. Neptune, which is Uranus' near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun.^[18] Uranus, by contrast, radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere.^[60][10] In fact, Uranus' heat flux is only 0.042 ± 0.047 W/m², which is lower than the internal heat flux of Earth of about 0.075 W/m².^[60] The lowest temperature recorded in Uranus' tropopause is 49 K (−224 °C), making Uranus the coldest planet in the Solar System.^[60][10] Internal heat is the heat source from the interior celestial objects, such as planets, brown dwarfs, and stars, caused by gravity and decaying radioactive materials. ... For other uses, see Neptune (disambiguation). ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... Atmospheres redirects here. ... flux in science and mathematics. ...

Hypotheses for this discrepancy include that when Uranus was "knocked over" by the supermassive impactor which caused its extreme axial tilt, the event also caused it to expel most of its primordial heat, leaving it with a depleted core temperature.^[61] Another hypothesis is that some form of barrier exists in Uranus' upper layers which prevents the core's heat from reaching the surface.^[9] For example, convection may take place in a set of compositionally different layers, which may inhibit the upward heat transport.^[10][60] Convection in the most general terms refers to the movement of currents within fluids (i. ... Heat conduction or thermal conduction is the spontaneous transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences. ...

Atmosphere

Main article: Atmosphere of Uranus

Although there is no well-defined solid surface within Uranus' interior, the outermost part of Uranus' gaseous envelope that is accessible to remote sensing is called its atmosphere.^[10] Remote sensing capability extends down to roughly 300 km below the 1 bar (100 kPa) level, with a corresponding pressure around 100 bar (10 MPa) and temperature of 320 K.^[62] The tenuous corona of the atmosphere extends remarkably over two planetary radii from the nominal surface at 1 bar pressure.^[63] The Uranian atmosphere can be divided into three layers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0.1 bar; (10 MPa to 10 kPa) the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10^–10 bar; (10 kPa to 10 µPa)and the thermosphere/corona extending from 4,000 km to as high as 50,000 km from the surface.^[10] There is no mesosphere. The bland face of Uranus, as imaged by Voyager 2 in 1986. ... Atmospheres redirects here. ... The kelvin (symbol: K) is the SI unit of temperature and is one of the seven SI base units. ... This article is about the astronomical term. ... Atmosphere diagram showing the mesosphere and other layers. ... Atmosphere diagram showing stratosphere. ... The pascal (symbol: Pa) is the SI unit of pressure. ... The thermosphere is the layer of the earths atmosphere directly above the mesosphere and directly below the exosphere. ... This article is about the astronomical term. ... The mesosphere (from the Greek words mesos = middle and sphaira = ball) is the layer of the Earths atmosphere that is directly above the stratosphere and directly below the thermosphere. ...