Uranus  

Uranus, as seen by Voyager 2
Discovery
Discovered by	William Herschel
Discovery date	March 13, 1781
Orbital characteristics[1][a]
Epoch J2000
Aphelion	3,004,419,704 km 20. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. Year 1781 ( MDCCLXXXI) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand 08330526 AU
Perihelion	2,748,938,461 km 18. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 37551863 AU
Semi-major axis	2,876,679,082 km 19. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 22941195 AU
Eccentricity	0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 044405586
Orbital period	30,799. The orbital period is the time taken for a given object to make one complete Orbit about another object 095 days 84. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the 323326 yr
Synodic period	369. In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined The orbital period is the time taken for a given object to make one complete Orbit about another object 66 days[2]
Average orbital speed	6. 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 81 km/s[2]
Mean anomaly	142. In the study of orbital dynamics the mean anomaly of an orbiting body is the Angle the body would have traveled about the center of the orbit's Auxiliary circle 955717°
Inclination	0. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 772556° 6. 48° to Sun's equator
Longitude of ascending node	73. The Sun (Sol is the Star at the center of the Solar System. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 989821°
Argument of perihelion	96. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 541318°
Satellites	27
Physical characteristics
Equatorial radius	25,559 ± 4 km 4. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Uranus has twenty-seven named moons. Five of them are massive enough to have achieved Hydrostatic equilibrium and so would be considered Dwarf planets The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the 007 Earths[3][c]
Polar radius	24,973 ± 20 km 3. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based 929 Earths[3][c]
Flattening	0. Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. 0229 ± 0. 0008[b]
Surface area	8. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 1156×109 km²[4][c] 15. 91 Earths
Volume	6. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 833×1013 km³[2][c] 63. 086 Earths
Mass	8. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 6810 ± 13×1025 kg 14. 536 Earths[5] GM=5,793,939 ± 13 km³/s²
Mean density	1. Small body orbiting a central body Under Standard assumptions in astrodynamics we have m where m \ is the mass The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 27 g/cm³[2][c]
Equatorial surface gravity	8. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 69 m/s²[2]<[c] 0. 886 g
Escape velocity	21. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 3 km/s[2][c]
Sidereal rotation period	−0. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. 71833 day 17 h 14 min 24 s[3]
Equatorial rotation velocity	2. The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI A minute is a Unit of measurement of Time or of Angle. The minute is a unit of Time equal to 1/60th of an Hour or 60 The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units 59 km/s 9,320 km/h
Axial tilt	97. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 77°[3]
North pole right ascension	17 h 9 min 15 s 257. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 311°[3]
North pole declination	−15. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 175°[3]
Albedo	0. The albedo of an object is the extent to which it diffusely reflects light from the sun 300 (bond) 0. 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 51 (geom.)[2]
Surface temp.    1 bar level[7]    0. The geometric albedo of an astronomical body is the ratio of its actual brightness at zero phase angle (i Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. 1 bar (tropopause)[8]	min mean max 76 K 49 K 53 K 57 K
Apparent magnitude	5. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 9[6] to 5. 32[2]
Angular diameter	3. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 3"–4. 1"[2]
Adjectives	Uranian
Atmosphere[8][9][10][d]
Scale height	27. A scale height is a term often used in scientific contexts for a distance over which a quantity decreases by a factor of e. 7 km[2]
Composition	(Below 1. 3 bar) 83 ± 3% Hydrogen (H2) 15 ± 3% Helium 2. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 3% Methane 0. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 009% (0. 007–0. 015%) Hydrogen deuteride (HD)[11] Ices: Ammonia water ammonium hydrosulfide (NH4SH) methane (CH4)

Uranus ([ˈjʊərənəs] (help·info) or [jʊˈreɪnəs] (help·info)^[12]) is the seventh planet from the Sun and the third-largest and fourth-most massive planet in the solar system. Hydrogen deuteride is a bi-atomic substance of the two isotopes of Hydrogen: the majority isotope 1H protium and 2H Deuterium Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ammonium hydrosulfide is the Chemical compound with the formula (NH4SH Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is The Sun (Sol is the Star at the center of the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. It is named after the ancient Greek deity of the sky (Uranus, Οὐρανός), the father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Uranus (ˈjʊərənəs jʊˈreɪnəs is the Latinized form of Ouranos () the Greek word for Sky. Cronus or Kronos, ( Ancient Greek Κρόνος Krónos) was the leader and the youngest of the first generation of Titans, divine descendants Saturn ( Latin: Saturnus) was a major Roman God of agriculture and harvest Zeus (zjuːs in Greek: nominative: Zeús /zdeús/ genitive: Diós; Modern Greek /'zefs/ in Greek mythology In Roman mythology, Jupiter was the king of the gods and the god of Sky and Thunder. Uranus was the first planet discovered in modern times. The term modern period or modern era (sometimes also modern times) is the period of history that followed the Middle Ages between c 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 and slow orbit. In Astronomy, the naked-eye planets are the five Planets of our Solar system that can be discerned with the Naked eye without much difficulty ^[13] 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. Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. Year 1781 ( MDCCLXXXI) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common The Solar System consists of the Sun and those celestial objects bound to it by Gravity. This was also the first discovery of a planet made using a telescope. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation.

Uranus is similar in internal and atmospheric composition to Neptune, and both have different compositions from those of the larger gas giants Jupiter and Saturn. Atmospheric chemistry is a branch of Atmospheric science in which the Chemistry of the Earth's atmosphere and that of other planets is studied Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily As such, astronomers sometimes place them in a separate category, the "ice giants". A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily 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. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C). The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The Celsius Temperature scale was previously known as the centigrade scale. 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. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body ^[8]

Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. 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. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation ^[14] Seen from Earth, Uranus' rings can sometimes 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. Modern competitive Archery is governed by the International Archery Federation, abbreviated FITA (Fédération Internationale de Tir à l'Arc 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. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface and strongly implying Severe weather. ^[14] However, terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle The wind speeds on Uranus can reach 250 meters per second. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) ^[15]

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. John Flamsteed FRS ( 19 August, 1646 - 31 December, 1719) was an English Astronomer and the first Taurus (it looks like a bull (ˈtɔrəs bull, symbol, Unicode ♉ is one of the Constellations of the Zodiac. The French astronomer, Pierre Lemonnier, observed Uranus at least twelve times between 1750 and 1769,^[16] including on four consecutive nights. There was also a French naval admiral Lemonnier Pierre Charles Le Monnier ( November 23, 1715 &ndash May 31, 1799

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),^[17] but initially reported it (on 26 April 1781) as a "comet". Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. Year 1781 ( MDCCLXXXI) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common Bath is a city in Somerset in the south west of England It is situated west of London and south-east of Bristol. Somerset ( or) is a county in south west England The County town is Taunton, which is in the south of the county 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 Events 1467 - The miraculous image in Our Lady of Good Counsel appear in Genazzano, Italy. Year 1781 ( MDCCLXXXI) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — ^[18] Herschel "engaged in a series of observations on the parallax of the fixed stars",^[19] using a telescope of his own design.

He recorded in his journal "In the quartile near ζ Tauri … either [a] Nebulous star or perhaps a comet". ^[20] 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". Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger ^[21] 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:^[22]

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. Astronomer Royal is a senior post in the Royal Household of the Sovereign of the United Kingdom. The Reverend Dr Nevil Maskelyne ( 6 October[[ 732]] &ndash 9 February[[ 811]] was the fifth English Astronomer Royal. Events 215 BC - A temple is built on the Capitoline Hill dedicated to Venus Erycina to commemorate the Roman defeat at 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". ^[23]

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. Anders Johan Lexell ( December 24 1740 &ndash December 11 1784 ( Julian calendar: November 30) was a Finland-Swedish In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from ^[24] 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". Johann Elert Bode ( January 19, 1747 &ndash November 23, 1826) was a German Astronomer known for his reformulation ^[25] Bode concluded that its near-circular orbit was more like a planet than a comet. ^[26]

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. Sir Joseph Banks 1st Baronet, GCB, PRS (13 February 1743 &ndash 19 June 1820 was an English naturalist, botanist and patron of "^[27] 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. George III (George William Frederick 4 June 1738 George III's long reign was marked by a series of military conflicts involving his kingdom much of the rest of Europe and places ^[28]

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. "^[29] 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. ^[30] He explained this decision in a letter to Joseph Banks:^[27]

William Herschel, discoverer of Uranus

Astronomer Jérôme Lalande proposed the planet be named Herschel in honour of its discoverer. Joseph Jérôme Lefrançais de Lalande ( July 11, 1732 &ndash April 4, 1807) was a French Astronomer and writer ^[31] Bode, however, opted for Uranus, the Latinized version of the Greek god of the sky, Ouranos. 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 Uranus (ˈjʊərənəs jʊˈreɪnəs is the Latinized form of Ouranos () the Greek word for Sky. Bode argued that just as Saturn was the father of Jupiter, the new planet should be named after the father of Saturn. ^[28][32][33] The earliest citation of the name Uranus in an official publication is in 1823, a year after Herschel's death. ^[34][35] 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. Her Majesty's Nautical Almanac Office ( HMNAO) now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Greenwich ^[32]

The preferred pronunciation of the name Uranus among astronomers is [ˈjʊərənəs], with the first syllable stressed and a short a (ūrănŭs);^[36] this is more classically correct than the alternate [jʊˈɹeɪ. A syllable ( Greek:) is a unit of organization for a sequence of speech sounds nəs], with stress on the second syllable and a "long a" (ūrānŭs), which is often used in the English-speaking world.

Uranus is the only planet whose name is derived from a figure from Greek mythology rather than Roman mythology. 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 Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its (The Roman equivalent would have been Caelus. Caelus, also known as Coelus, was the Roman god of the Sky, personified from the Latin word for "sky" caelum ) The adjective of Uranus is "Uranian". The element uranium, discovered in 1789, was named in its honour by its discoverer, Martin Klaproth. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Martin Heinrich Klaproth ( 1 December 1743 – 1 January 1817) was a German Chemist. ^[37]

Its astronomical symbol is . Astronomical symbols are symbols used to represent various Celestial objects theoretical constructs and observational events in Astronomy. 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. The Sun (Sol is the Star at the center of the Solar System. ^[38] Its astrological symbol is , suggested by Lalande in 1784. Astrological symbols are images used in various astrological systems to denote relevant objects 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"). ^[31] In the Chinese, Japanese, Korean, and Vietnamese languages, the planet's name is literally translated as the sky king star (天王星). is a language spoken by over 130 million people in Japan and in Japanese emigrant communities This article is mainly about the spoken Korean language See Hangul for details on the native Korean writing system Vietnamese ( tiếng Việt, or less commonly Việt ngữ) formerly known under French colonization as Annamese ( see Annam) ^[39][40]

Orbit and rotation

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

Uranus revolves around the Sun once every 84 Earth years. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Its average distance from the Sun is roughly 3 billion km (about 20 AU). The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The intensity of sunlight on Uranus is about 1/400 that of Earth. ^[41] Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace. ^[24] 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. John Couch Adams ( June 5 1819 &ndash January 21, 1892) was a British Mathematician and Astronomer In 1845, Urbain Le Verrier began his own independent research into Uranus' orbit. Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial On September 23, 1846, Johann Gottfried Galle located a new planet, later named Neptune, at nearly the position predicted by Le Verrier. Events 1122 - Concordat of Worms. 1459 - Battle of Blore Heath, the first major battle of the English For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[42]

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. ^[43]

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. A top, or spinning top, is a Toy that can be spun on an axis balancing on a point BALL ( Biochemical Algorithms Library) is a C++ library containing common algorithms used in Biochemistry and Bioinformatics. Near the time of Uranian solstices, one pole faces the Sun continually while the other pole faces away. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes The Sun (Sol is the Star at the center of the Solar System. 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. ^[44] 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. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Uranus reached its most recent equinox on 7 December 2007. Events 43 BC - Marcus Tullius Cicero assassinated 1696 - Connecticut Route 108, one of the oldest highways Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. ^[45][46]

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. Protoplanets are moon-sized planets or larger embryos within Protoplanetary discs They are believed to form out of kilometer-sized Planetesimals that attract each ^[47] Uranus' south pole was pointed almost directly at the Sun at the time of Voyager 2's flyby in 1986. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. 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. ^[48][49] 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. For the related yet different principle relating to electromagnetic coils see Right hand grip rule. ^[50] 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!"^[51]

Visibility

From 1995 to 2006, Uranus' apparent magnitude fluctuated between +5. Sir Alfred Patrick Caldwell-Moore, CBE, HonFRS, FRAS (born 4 March 1923 in Pinner) known as Patrick Moore, is The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 6 and +5. 9, placing it just within the limit of naked eye visibility at +6. The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or 5. ^[6] 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. ^[6] 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. Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects ^[4] 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. Limb darkening refers to the diminishing of intensity in the image of a star as one moves from the center of the image to the edge or " Limb " of the image 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. Titania (, also) is the largest moon of Uranus and the eighth largest moon in the Solar System. TemplateInfobox Planet.--> Oberon (ˈoʊbərɒn) is the outermost ^[52]

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. ^[5] Though having a diameter slightly larger than Neptune (roughly four times Earth's), it is less massive. ^[3] These values indicate that it is made primarily of various ices, such as water, ammonia, and methane. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ^[7] 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. ^[7][53] Hydrogen and helium constitute only a small part of the total, with between 0. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 5 and 1. 5 Earth masses. ^[7] The remainder of the mass (0. 5 to 3. 7 Earth masses) is accounted for by rocky material. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere ^[7]

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. The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical ^[7][54] 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. ^[7][54] 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. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic ^[53][54] 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. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's ^[7][54] This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean. ^[55] 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. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily

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. ^[53] The fluid interior structure of Uranus means that it has no solid surface. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. The gaseous atmosphere gradually transitions into the internal liquid layers. ^[7] However for the sake of convenience an oblate spheroid of revolution, where pressure equals 1 bar (100 kPa), is designated conditionally as a ‘surface’. An oblate Spheroid is a rotationally symmetric Ellipsoid having a polar axis shorter than the diameter of the equatorial circle whose plane The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. It has equatorial and polar radii of 25,559 ± 4 and 24,973 ± 20 km, respectively. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based ^[3] This surface will be used throughout this article as a zero point for altitudes. Altitude is the Elevation of a point or object from a known level or datum (plural data

Internal heat

Uranus' internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low thermal flux. Internal heat is the Heat source from the interior Celestial objects such as Planets Brown dwarfs and Stars caused by Gravity Heat Flux or thermal flux is a flow of Energy per unit of area per unit of time ^[56][15] Why Uranus' internal temperature is so low is still not understood. Neptune, which is Uranus' near twin in size and composition, radiates 2. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. 61 times as much energy into space as it receives from the Sun. ^[15] Uranus, by contrast, radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of e. heat) part of the spectrum is 1. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature 06 ± 0. 08 times the solar energy absorbed in its atmosphere. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " ^[57][8] 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. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks ^[57] The lowest temperature recorded in Uranus' tropopause is 49 K (−224 °C), making Uranus the coldest planet in the Solar System. ^[57][8]

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. ^[58] Another hypothesis is that some form of barrier exists in Uranus' upper layers which prevents the core's heat from reaching the surface. ^[7] For example, convection may take place in a set of compositionally different layers, which may inhibit the upward heat transport. Convection in the most general terms refers to the movement of molecules 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 ^[8][57]

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. The atmosphere of Uranus, like that of Neptune, is markedly different from those of the larger Gas giants Jupiter and Saturn. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " ^[8] 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. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic ^[59] The tenuous corona of the atmosphere extends remarkably over two planetary radii from the nominal surface at 1 bar pressure. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily ^[60] The Uranian atmosphere can be divided into three layers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and 1 bar; (10 MPa to 10 kPa) the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. 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. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily ^[8] There is no mesosphere. This article is about the atmospheric mesosphere for the Earth's mantle see Mesosphere (mantle.

Composition

The composition of the Uranian atmosphere is different from the composition of Uranus as a whole, consisting as it does mainly of molecular hydrogen and helium. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical ^[8] The helium molar fraction, i. e. the number of helium atoms per molecule of gas, is 0. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by 15 ± 0. 03^[10] in the upper troposphere, which corresponds to a mass fraction 0. 26 ± 0. 05. ^[8][57] This value is very close to the protosolar helium mass fraction of 0. 275 ± 0. 01,^[61] indicating that helium has not settled in the center of the planet as it has in the gas giants. ^[8] The third most abundant constituent of the Uranian atmosphere is methane (CH₄). An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ^[8] Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color. An absorption band is a range of Wavelengths (or equivalently frequencies) in the Electromagnetic spectrum which are able to excite a particular For other uses see Visibility. Visible is billed as a not-for-profit free quarterly magazine dedicated to the history of Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Aquamarine is Color that is a Tint of Cyan.It is named after the mineral Aquamarine. Cyan (saɪæn from Greek κυανός / kyanos, meaning "blue" may be used as the name of any of a number of a range of colors in the blue/green part of ^[8] Methane molecules account for 2. 3% of the atmosphere by molar fraction below the methane cloud deck at the pressure level of 1. 3 bar (130 kPa); this represents about 20 to 30 times the carbon abundance found in the Sun. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. ^[8][9][62] The mixing ratio^[e] is much lower in the upper atmosphere due to its extremely low temperature, which lowers the saturation level and causes excess methane to freeze out. ^[63] The abundances of less volatile compounds such as ammonia, water and hydrogen sulfide in the deep atmosphere are poorly known. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Water is a common Chemical substance that is essential for the survival of all known forms of Life. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. However they are probably also higher than solar values. ^[8][64] In addition to methane, trace amounts of various hydrocarbons are found in the stratosphere of Uranus, which are thought to be produced from methane by photolysis induced by the solar ultraviolet (UV) radiation. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. Photodissociation, photolysis, or photodecomposition is a Chemical reaction in which a Chemical compound is broken down by Photons Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays ^[65] They include ethane (C₂H₆), acetylene (C₂H₂), methylacetylene (CH₃C₂H), diacetylene (C₂HC₂H). ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes Methylacetylene ( propyne) is an Alkyne with the Chemical formula H 3C≡CH Diacetylene (also known as butadiyne) with the formula C4H2 is a highly unsaturated Hydrocarbon that contains one Single bond ^[63][66][67] Spectroscopy has also uncovered traces of water vapor, carbon monoxide and carbon dioxide in the upper atmosphere, which can only originate from an external source such as infalling dust and comets. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — ^[67][66][68]

Troposphere

Temperature profile of the Uranian troposphere and lower stratosphere. Cloud and haze layers are also indicated.

The troposphere is the lowest and densest part of the atmosphere and is characterized by a decrease in temperature with altitude. ^[8] The temperature falls from about 320 K at the base of the nominal troposphere at −300 km to 53 K at 50 km. ^[59][62] The temperatures in the coldest upper region of the troposphere (the tropopause) actually vary in the range between 49 and 57 K depending on planetary latitude. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. ^[8][56] The tropopause region is responsible for the vast majority of the planet’s thermal far infrared emissions, thus determining its effective temperature of 59. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Star The effective temperature of a Star is the temperature of a Black body with the same luminosity per surface area (\mathcal{F}_{Bol} 1 ± 0. 3 K. ^[56][57]

The troposphere is believed to possess a highly complex cloud structure; water clouds are hypothesised to lie in the pressure range of 50 to 100 bar (5 to 10 MPa), ammonium hydrosulfide clouds in the range of 20 to 40 bar (2 to 4 MPa), ammonia or hydrogen sulfide clouds at between 3 and 10 bar (0. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body Ammonium hydrosulfide is the Chemical compound with the formula (NH4SH Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. 3 to 1 MPa) and finally directly detected thin methane clouds at 1 to 2 bar (0. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 1 to 0. 2 MPa). ^{[8][59][69][9]} The troposphere is a very dynamic part of the atmosphere, exhibiting strong winds, bright clouds and seasonal changes, which will be discussed below. ^[15]

Upper atmosphere

The middle layer of the Uranian atmosphere is the stratosphere, where temperature generally increases with altitude from 53 K in the tropopause to between 800 and 850 K at the base of the thermosphere. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. ^[60] The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons,^[70] which form in this part of the atmosphere as a result of methane photolysis. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. Photodissociation, photolysis, or photodecomposition is a Chemical reaction in which a Chemical compound is broken down by Photons ^[65] Heat is also conducted from the hot thermosphere. ^[70] The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 280 km corresponding to a pressure range of 10 to 0. 1 mbar (1000 to 10 kPa) and temperatures of between 75 and 170 K. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. ^[63][66] The most abundant hydrocarbons are methane, acetylene and ethane with mixing ratios of around 10⁻⁷ relative to hydrogen. Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 The mixing ratio of carbon monoxide is similar at these altitudes. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. ^[63][66][68] Heavier hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single ^[66] The abundance ratio of water is around 7×10⁻⁹. ^[67] Ethane and acetylene tend to condense in the colder lower part of stratosphere and tropopause (below 10 mBar level) forming haze layers,^[65] which may be partly responsible for the bland appearance of Uranus. Haze is traditionally an atmospheric phenomenon where dust smoke and other dry particles obscure the clarity of the sky However, the concentration of hydrocarbons in the Uranian stratosphere above the haze is significantly lower than in the stratospheres of the other giant planets. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily ^[63][71]

The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature around 800 to 850 K. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily ^[8][71] The heat sources necessary to sustain such a high value are not understood, since neither solar far UV and extreme UV radiation nor auroral activity can provide the necessary energy. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0. 1 mBar pressure level may contribute too. ^[60][71] In addition to molecular hydrogen, the thermosphere-corona contains a large proportion of free hydrogen atoms. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 A hydrogen atom is an atom of the chemical element Hydrogen. The electrically neutral Their small mass together with the high temperatures explain why the corona extends as far as 50,000 km or two Uranian radii from the planet. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily ^[60][71] This extended corona is a unique feature of Uranus. ^[71] Its effects include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a Dust is a general name for minute Solid particles with Diameters less than 500 micrometers. ^[60] The Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation ^[62] Observations show that the ionosphere occupies altitudes from 2,000 to 10,000 km. ^[62] The Uranian ionosphere is denser than that of either Saturn or Neptune, which may arise from the low concentration of hydrocarbons in the stratosphere. ^[71][72] The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity. Solar variations are changes in the amount of Solar radiation emitted by the Sun. ^[73] Auroral activity is insignificant as compared to Jupiter and Saturn. ^[71][74]

Planetary rings

Main article: Rings of Uranus

Uranus' inner rings. The planet Uranus has a system of rings intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and The bright outer ring is the epsilon ring, eight other rings are present

An enhanced colour schematic of the inner rings

Uranus has a faint planetary ring system, composed of dark particulate matter up to ten meters in diameter. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region ^[14] It was the second ring system to be discovered in the Solar System after Saturn's. Saturn has the most extensive Planetary ring system of any planet in the Solar System. ^[75] Thirteen distinct rings are presently known, the brightest being the epsilon ring. Uranus’ rings are probably quite young; gaps in their circumference as well as differences in their opacity suggest that they did not form with Uranus. The matter in the rings may once have been part of a moon which was shattered by a high-speed impact or tidal forces. ^[75][76]

William Herschel claimed to have seen rings at Uranus in 1789 (see below), however this is doubtful as in the two following centuries no rings were noted by other observers. Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British The ring system was definitively discovered on March 10, 1977 by James L. Elliot, Edward W. Events 241 BC - First Punic War: Battle of the Aegates Islands - The Romans sink the Carthaginian fleet bringing Also 1977 (album by Ash. Year 1977 ( MCMLXXVII) was a Common year starting on Saturday (link displays James L Elliot is a Professor of Physics Professor of Earth Atmospheric and Planetary Sciences and the Director George R Dunham, and Douglas J. Mink using the Kuiper Airborne Observatory. Douglas J Mink is an Astronomical Software Developer and Data Archivist at the Harvard-Smithsonian Center for Astrophysics The Gerard P Kuiper Airborne Observatory (KAO was a national facility operated by NASA to support research in Infrared astronomy. The discovery was serendipitous; they planned to use the occultation of the star SAO 158687 by Uranus to study the planet's atmosphere. In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " However, when their observations were analyzed, they found that the star had disappeared briefly from view five times both before and after it disappeared behind the planet. They concluded that there must be a ring system around the planet. ^[77] The rings were directly imaged when Voyager 2 passed Uranus in 1986. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[14] Voyager 2 also discovered two additional faint rings bringing the total number to eleven. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[14]

In December 2005, the Hubble Space Telescope detected a pair of previously unknown rings. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into The largest is located at twice the distance from the planet of the previously known rings. These new rings are so far from the planet that they are being called the "outer" ring system. Hubble also spotted two small satellites, one of which, Mab, shares its orbit with the outermost newly discovered ring. The new rings bring the total number of Uranian rings to 13. ^[78] In April 2006, images of the new rings with the Keck Observatory yielded the colours of the outer rings: the outermost is blue and the other red. The W M Keck Observatory is a two-telescope Astronomical observatory at the 4145 meter (13600 ft summit of Mauna Kea in Hawai'i. ^[79][80] One hypothesis concerning the outer ring's blue colour is that it is composed of minute particles of water ice from the surface of Mab that are small enough to scatter blue light. ^[79][81] The planet's inner rings appear grey. ^[79] Regarding William Herschel's observations in the 18th century, the first mention of a Uranian ring system comes from his notes detailing his observations of Uranus, which include the following passage: "February 22, 1789: A ring was suspected". Events 1495 - King Charles VIII of France enters Naples to claim the city's throne Year 1789 ( MDCCLXXXIX) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Common ^[82] Herschel drew a small diagram of the ring and noted that it was "a little inclined to the red". The Keck Telescope in Hawaii has since confirmed this to be the case. ^[79] Herschel's notes were published in a Royal Society journal in 1797. However, in the two centuries between 1797 and 1977 the rings are rarely mentioned, if at all. This casts serious doubt whether Herschel could have seen anything of the sort while hundreds of other astronomers saw nothing. Still, it has been claimed by some that Herschel actually gave accurate descriptions of the ring's size relative to Uranus, its changes as Uranus travelled around the Sun, and its colour. ^[83]

Magnetic field

The magnetic field of Uranus as seen by Voyager 2 in 1986. S and N are magnetic south and north poles.

Prior to the arrival of Voyager 2, no measurements of the Uranian magnetosphere had been taken, so its nature remained a mystery. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. Before 1986, astronomers had expected the magnetic field of Uranus to be in line with the solar wind, since it would then align with the planet's poles that lie in the ecliptic. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The ecliptic is the apparent path that the Sun traces out in the sky during the year ^[84]

Voyager's observations revealed that the magnetic field is peculiar, both because it does not originate from the planet's geometric center, and because it is tilted at 59° from the axis of rotation. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges ^[84][85] In fact the magnetic dipole is shifted from the center of the planet towards the south rotational pole by as much as one third of the planetary radius. ^[84] This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0. 1 gauss (10 µT), whereas in the northern hemisphere it can be as high 1. The gauss, abbreviated as G is the Cgs unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic 1 gauss (110 µT). ^[84] The average field at the surface is 0. 23 gauss (23 µT). ^[84] In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its physical equator. ^[85] The dipole moment of Uranus is 50 times that of Earth. ^[84][85] Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants. ^[85] One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giant planets, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean. ^[55][86]

Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a bow shock located at about 23 Uranian radii ahead of it, a magnetopause at 18 Uranian radii, a fully developed magnetotail and radiation belts. A bow shock is a boundary between a Magnetosphere and an ambient medium A magnetopause flows along the boundary between a Magnetic field, (see Magnetosphere) and surrounding plasma. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The Van Allen radiation belt is a Torus of energetic Charged particles ( plasma) around Earth, held in place by Earth's Magnetic ^[84][85][87] Overall, the structure of the magnetosphere of Uranus is different from that of Jupiter's and more similar to that of Saturn's. ^[84][85] Uranus' magnetotail trails behind the planet into space for millions of kilometers and is twisted by the planet's sideways rotation into a long corkscrew. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. ^[84][88]

Uranus' magnetosphere contains charged particles: protons and electrons with small amount of H₂⁺ ions. In Physics, a charged particle is a particle with an Electric charge. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge ^[85][87] No heavier ions have been detected. Many of these particles probably derive from the hot atmospheric corona. ^[87] The ion and electron energies can be as high as 4 and 1. 2 megaelectronvolts, respectively. ^[87] The density of low energy (below 1 kiloelectronvolt) ions in the inner magnetosphere is about 2 cm⁻³. ^[89] The particle population is strongly affected by the Uranian moons that sweep through the magnetosphere leaving noticeable gaps. ^[87] The particle flux is high enough to cause darkening or space weathering of the moon’s surfaces on an astronomically rapid timescale of 100,000 years. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment ^[87] This may be the cause of the uniformly dark colouration of the moons and rings. ^[76] Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles. ^[71] However, unlike Jupiter's, Uranus' aurorae seem to be insignificant for the energy balance of the planetary thermosphere. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. ^[74]

Climate

Main article: Climate of Uranus

Uranus' southern hemisphere in approximate natural colour (left) and in higher wavelengths (right), showing its faint cloud bands and atmospheric "hood" as seen by Voyager 2

Uranus' atmosphere is remarkably bland in comparison to the other gas giants, even to Neptune, which it otherwise closely resembles. The climate of Uranus is heavily influenced by both its lack of internal heat which limits atmospheric activity and by its extreme axial tilt which induces extreme seasonal ^[15] When Voyager 2 flew by Uranus in 1986, it observed a total of ten cloud features across the entire planet. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[14][90] One proposed explanation for this dearth of features is that Uranus' internal heat appears markedly lower than that of the other giant planets. Internal heat is the Heat source from the interior Celestial objects such as Planets Brown dwarfs and Stars caused by Gravity The lowest temperature recorded in Uranus' tropopause is 49 K, making Uranus the coldest planet in the Solar System, colder than Neptune. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[57][8]

Banded structure, winds and clouds

Zonal wind speeds on Uranus. Shaded areas show the southern collar and its future northern counterpart. The red curve is a symmetrical fit to the data.

In 1986 Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions: a bright polar cap and dark equatorial bands (see figure on the right). Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[14] Their boundary is located at about −45 degrees of latitude. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the A narrow band straddling the latitudinal range from −45 to −50 degrees is the brightest large feature on the visible surface of the planet. ^[14][91] It is called a southern "collar". The cap and collar are thought to be a dense region of methane clouds located within the pressure range of 1. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 3 to 2 bar (see above). The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. ^[92] Unfortunately Voyager 2 arrived during the height of the planet's southern summer and could not observe the northern hemisphere. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. However, at the beginning of the twenty-first century, when the northern polar region came into view, Hubble Space Telescope (HST) and Keck telescope observed neither a collar nor a polar cap in the northern hemisphere. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into The W M Keck Observatory is a two-telescope Astronomical observatory at the 4145 meter (13600 ft summit of Mauna Kea in Hawai'i. ^[91] So Uranus appears to be asymmetric: bright near the south pole and uniformly dark in the region north of the southern collar. ^[91]

In addition to large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to the north from the collar. ^[14] In all other respects Uranus looked like a dynamically dead planet in 1986. However in the 1990s the number of the observed bright cloud features grew considerably. ^[15] The majority of them were found in the northern hemisphere as it started to become visible. ^[15] The common explanation of this fact is that bright clouds are easier to identify in the dark part of the planet, whereas in the southern hemisphere the bright collar masks them. ^[93] Nevertheless there are differences between the clouds of each hemisphere. The northern clouds are smaller, sharper and brighter. ^[94] They appear to lie at a higher altitude. Altitude is the Elevation of a point or object from a known level or datum (plural data ^[94] The lifetime of clouds spans several orders of magnitude. Some small clouds live for hours, while at least one southern cloud has persisted since Voyager flyby. ^[15][90] Recent observation also discovered that cloud-features on Uranus have a lot in common with those on Neptune, although the weather on Uranus is much calmer. ^[15] The dark spots common on Neptune had never been observed on Uranus before 2006, when the first such feature was imaged. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[95]

The first dark spot observed on Uranus. Image obtained by ACS on HST in 2006. The Advanced Camera for Surveys (ACS is a third generation axial instrument aboard the Hubble Space Telescope (HST The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into

The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of Uranus. The terms zonal and meridional are used to describe directions on a Globe. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and ^[15] At the equator winds are retrograde, which means that they blow in the reverse direction to the planetary rotation. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the Their speeds are from −100 to −50 m/s. ^[15][91] Wind speeds increase with the distance from the equator, reaching zero values near ±20° latitude, where the troposphere's temperature minimum is located. ^[56][15] Closer to the poles, the winds shift to a prograde direction, flowing with the planet's rotation. Windspeeds continue to increase reaching maxima at ±60° latitude before falling to zero at the poles. ^[15] Windspeeds at −40° latitude range from 150 to 200 m/s. Since the collar obscures all clouds below that parallel, speeds between it and the southern pole are impossible to measure. ^[15] In contrast, in the northern hemisphere maximum speeds as high as 240 m/s are observed near +50 degrees of latitude. ^[15][91][96]

Seasonal variation

Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible.

For a short period from March to May 2004, a number of large clouds appeared in the Uranian atmosphere, giving it a Neptune-like appearance. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[94][97] Observations included record-breaking wind speeds of 229 m/s (824 km/h) and a persistent thunderstorm referred to as "Fourth of July fireworks". ^[90] On August 23, 2006, researchers at the Space Science Institute (Boulder, CO) and the University of Wisconsin observed a dark spot on Uranus' surface, giving astronomers more insight into the planet's atmospheric activity. Events 79 - Mount Vesuvius begins stirring on the feast day of Vulcan the Roman god of fire Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. ^[95] Why this sudden upsurge in activity should be occurring is not fully known, but it appears that Uranus' extreme axial tilt results in extreme seasonal variations in its weather. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. A season is one of the major divisions of the Year, generally based on yearly periodic changes in Weather. ^[46][98] Determining the nature of this seasonal variation is difficult because good data on Uranus' atmosphere has existed for less than 84 years, or one full Uranian year. A number of discoveries have however been made. Photometry over the course of half a Uranian year (beginning in the 1950s) has shown regular variation in the brightness in two spectral bands, with maxima occurring at the solstices and minima occurring at the equinoxes. Photometry is a technique of Astronomy concerned with measuring the Flux, or intensity of an Astronomical object 's Electromagnetic Spectral bands are part of optical spectra of polyatomic systems including condensed materials large molecules etc Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes An equinox is the event of the Sun passing over the Earth's equator in its annual cycle ^[99] A similar periodic variation, with maxima at the solstices, has been noted in microwave measurements of the deep troposphere begun in the 1960s. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 ^[100] Stratospheric temperature measurements beginning in 1970s also showed maximum values near 1986 solstice. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. ^[70] The majority of this variability is believed to occur due to changes in the viewing geometry. Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position ^[93]

However there are some reasons to believe that physical seasonal changes are happening in Uranus. While the planet is known to have a bright south polar region, the north pole is fairly dim, which is incompatible with the model of the seasonal change outlined above. ^[98] During its previous northern solstice in 1944, Uranus displayed elevated levels of brightness, which suggests that the north pole was not always so dim. ^[99] This information implies that the visible pole brightens some time before the solstice and darkens after the equinox. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle ^[98] Detailed analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the solstices, which also indicates a change in the meridional albedo patterns. For other uses see Visibility. Visible is billed as a not-for-profit free quarterly magazine dedicated to the history of Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 The terms zonal and meridional are used to describe directions on a Globe. The albedo of an object is the extent to which it diffusely reflects light from the sun ^[98] Finally in the 1990s, as Uranus moved away from its solstice, Hubble and ground based telescopes revealed that the south polar cap darkened noticeably (except the southern collar, which remained bright),^[92] while the northern hemisphere demonstrates increasing activity,^[90] such as cloud formations and stronger winds, bolstering expectations that it should brighten soon. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[94]

The mechanism of physical changes is still not clear. ^[98] Near the summer and winter solstices, Uranus' hemispheres lie alternately either in full glare of the Sun's rays or facing deep space. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes The brightening of the sunlit hemisphere is thought to result from the local thickening of the methane clouds and haze layers located in the troposphere. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body Haze is traditionally an atmospheric phenomenon where dust smoke and other dry particles obscure the clarity of the sky The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and ^[92] The bright collar at −45° latitude is also connected with methane clouds. ^[92] Other changes in the southern polar region can be explained by changes in the lower cloud layers. ^[92] The variation of the microwave emission from the planet is probably caused by a changes in the deep tropospheric circulation, because thick polar clouds and haze may inhibit convection. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 In Physics, emission is the process by which the Energy of a Photon is released by another entity for example by an Atom whose Electrons In Fluid dynamics, circulation is the Line integral around a closed curve of the Fluid Velocity. ^[101] Now that the spring and autumn equinoxes are arriving on Uranus, the dynamics are changing and convection can occur again. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle ^[90][101]

Formation

See also: Nebular hypothesis

Many argue that the differences between the ice giants and the gas giants extend to their formation. In Cosmogony, the nebular hypothesis is the most widely accepted model explaining the Formation and evolution of the Solar System. ^[102][103] The Solar System is believed to have formed from a giant rotating ball of gas and dust known as the presolar nebula. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. In Cosmogony, the nebular hypothesis is the most widely accepted model explaining the Formation and evolution of the Solar System. As it condensed, it formed into a disc with a slowly collapsing Sun in the middle. ^[102][103] Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, while the dust grains collected together to form the first protoplanets. As the planets grew, some of them eventually accreted enough matter for their gravity to hold onto the nebula's leftover gas. ^[102][103] The more gas they held onto, the larger they became; the larger they became, the more gas they held onto until a critical point was reached, and their size began to increase exponentially. The ice giants, with only a few Earth masses of nebular gas, never reached that critical point. ^{[103][104][102]} Current theories of solar system formation have difficulty accounting for the presence of Uranus and Neptune so far out from Jupiter and Saturn. They are too large to have formed from the amount of material expected at that distance. Rather, some scientists expect that both formed closer to the Sun but were scattered outward by Jupiter. ^[102] However, more recent simulations, which take into account planetary migration, seem to be able to form Uranus and Neptune near their present locations. Planetary migration occurs when a Planet or other stellar satellite interacts with a disk of gas or Planetesimals resulting in the alteration of the satellite's orbital ^[103]

Moons

Main article: Moons of Uranus

See also: Timeline of discovery of Solar System planets and their natural satellites

Major moons of Uranus compared, at their proper relative sizes (montage of Voyager 2 photographs)

Uranus has 27 known natural satellites. Uranus has twenty-seven named moons. Five of them are massive enough to have achieved Hydrostatic equilibrium and so would be considered Dwarf planets Wikipedia talkFeatured lists for an explanation of this and other inclusion tags below-->This timeline of discovery of Solar System planets and their natural Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. ^[104] The names for these satellites are chosen from characters from the works of Shakespeare and Alexander Pope. William Shakespeare ( baptised Alexander Pope (21 May 1688 – 30 May 1744 is generally regarded as the greatest English Poet of the eighteenth century best known for his Satirical ^[54][105] The five main satellites are Miranda, Ariel, Umbriel, Titania and Oberon. TemplateInfobox Planet.--> Miranda (mɨˈrændə) is the smallest TemplateInfobox Planet.--> Ariel (ˈɛəriəl) is a moon Umbriel (ˈʌmbriəl) is a moon of Uranus discovered on October 24, 1851 by William Lassell. Titania (, also) is the largest moon of Uranus and the eighth largest moon in the Solar System. TemplateInfobox Planet.--> Oberon (ˈoʊbərɒn) is the outermost ^[54] The Uranian satellite system is the least massive among the gas giants; indeed, the combined mass of the five major satellites would be less than half that of Triton alone. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek ^[5] The largest of the satellites, Titania, has a radius of only 788. 9 km, or less than half that of the Moon, but slightly more than Rhea, the second largest moon of Saturn, making Titania the eighth largest moon in the Solar System. The tables below of Natural satellites in the Solar System are ordered from largest to smallest by average diameter The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The moons have relatively low albedos; ranging from 0. The albedo of an object is the extent to which it diffusely reflects light from the sun 20 for Umbriel to 0. Umbriel (ˈʌmbriəl) is a moon of Uranus discovered on October 24, 1851 by William Lassell. 35 for Ariel (in green light). TemplateInfobox Planet.--> Ariel (ˈɛəriəl) is a moon ^[14] The moons are ice-rock conglomerates composed of roughly fifty percent ice and fifty percent rock. The ice may include ammonia and carbon dioxide. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single ^[106][76]

Among the satellites, Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest. ^[14][76] Miranda possesses fault canyons 20 kilometers deep, terraced layers, and a chaotic variation in surface ages and features. TemplateInfobox Planet.--> Miranda (mɨˈrændə) is the smallest ^[14] Miranda's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently, probably as a result of a formerly present 3:1 orbital resonance with Umbriel. Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i In Celestial mechanics, an orbital resonance occurs when two Orbiting bodies exert a regular periodic gravitational influence on each other usually due to their ^[107] Extensional processes associated with upwelling diapirs are likely the origin of the moon's 'racetrack'-like coronae. In Geology, a rift is a place where the Earth 's crust and Lithosphere are being pulled apart and is an example of Extensional tectonics A diapir (ˈdaɪəpɪər) ( French, from Greek diapeirein, to pierce through is an Intrusion caused by Buoyancy and Pressure In Planetary geology, a corona (plural coronae) is an Oval -shaped feature ^[108][109] Similarly, Ariel is believed to have once been held in a 4:1 resonance with Titania. ^[110]

A picture of Uranus taken by Voyager 2 as it headed to Neptune

Exploration

Main article: Exploration of Uranus

In 1986, NASA's Voyager 2 visited Uranus. The exploration of Uranus has been solely through the Voyager 2 spacecraft with no other visits currently planned The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. This visit is the only attempt to investigate the planet from a short distance and no other visits are currently planned. Launched in 1977, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers of the planet's cloud tops, before continuing its journey to Neptune. Events 41 - Gaius Caesar (Caligula, known for his eccentricity and cruel Despotism, is Assassinated by his disgruntled Year 1986 ( MCMLXXXVI) was a Common year starting on Wednesday (link displays 1986 Gregorian calendar) Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Voyager 2 studied structure and chemical composition of the atmosphere,^[62] discovered 10 new moons and studied the planet's unique weather, caused by its axial tilt of 97. Uranus has twenty-seven named moons. Five of them are massive enough to have achieved Hydrostatic equilibrium and so would be considered Dwarf planets In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 77°; and examined its ring system. The planet Uranus has a system of rings intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and ^[111][14] It also studied the magnetic field, its irregular structure, its tilt and its unique corkscrew magnetotail brought on by Uranus' sideways orientation. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. ^[84] It made the first detailed investigations of its five largest moons, and studied all nine of the system's known rings, discovering two new ones. ^[76][14]

See also

• Colonization of Uranus
• Uranus in astrology
• Uranus in fiction

Notes

References

External links

• Edge On! ESO Press Release
• NASA's Uranus fact sheet
• Uranus Profile by NASA's Solar System Exploration
• Keck pictures of Uranus show best view from the ground—Press release with some photographs showing rings, satellites and clouds
• News reports of December 22, 2005 rings and moons discovery
  • New Moons and Rings found at Uranus, SPACE.com
  • Two more rings discovered around Uranus, MSNBC
• Planets—Uranus A kid's guide to Uranus. Events 1790 - The Turkish fortress of Izmail is stormed and captured by Suvorov and his Russian armies Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Spacecom is a Space and Astronomy news website Its stories are often syndicated to other media outlets including CNN, MSNBC MSNBC is a 24-hour cable television news channel based in the United States and available in Canada.
• Uranus at Jet Propulsion Laboratory's planetary photojournal.
• Spring Has Sprung on Uranus
• Astronomy Cast: Uranus