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115-463: If the closer body does not entirely conceal the farther one, the event is called a transit . Both transit and occultation may be referred to generally as occlusion ; and if a shadow is cast onto the observer, it is called an eclipse . The symbol for an occultation, and especially a solar eclipse , is [REDACTED] (U+1F775 🝵). The term occultation is most frequently used to describe lunar occultations , those relatively frequent occasions when

230-470: A fundamental prerequisite for Maarten Schmidt 's discovery of the cosmological nature of quasars . Several times during the year the Moon can be seen occulting a planet. Since planets, unlike stars, have significant angular sizes, lunar occultations of planets will create a narrow zone on Earth from which a partial occultation of the planet will occur. An observer located within that narrow zone could observe

345-509: A space telescope , most likely positioned near the Earth 's L 2 Lagrangian point . The second would place the satellite in a highly elliptical orbit about the Earth, and work in conjunction with a ground telescope. At the apogee of the orbit, the satellite would remain relatively stationary with respect to the ground, allowing longer exposure times. An updated version of this design is called

460-404: A bright spot at the north pole, indicating the presence of a polar vortex . In the 1990s, the number of the observed bright cloud features grew considerably, partly because new high-resolution imaging techniques became available. Most were found in the northern hemisphere as it started to become visible. An early explanation—that bright clouds are easier to identify in its dark part, whereas in

575-608: A comet." On 17 March he noted: "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place." When he presented his discovery to the Royal Society , he continued to assert that he had found a comet, but also implicitly compared it to a planet: The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put

690-512: A few Earth masses of nebular gas, never reached that critical point. Recent simulations of planetary migration have suggested that both ice giants formed closer to the Sun than their present positions, and moved outwards after formation (the Nice model ). Uranus orbits the Sun once every 84 years. As viewed against the background of stars, since being discovered in 1781, the planet has returned to

805-420: A good technique for discovering exoplanets. In recent years, the discovery of extrasolar planets has prompted interest in the possibility of detecting their transits across their own stellar primaries. HD 209458b was the first such transiting planet to be detected. The transit of celestial objects is one of the few key phenomena used today for the study of exoplanetary systems. Today, transit photometry

920-700: A large area of the sky for possible transiting planets. In addition, their multitude and spread around the world allows for 24/7 observation of the sky so that more short-period transits can be caught. A third sub-project, HATPI, is currently under construction and will survey most of the night sky seen from its location in Chile. KELT is a terrestrial telescope mission designed to search for transiting systems of planets of magnitude 8<M<10. It began operation in October 2004 in Winer Observatory and has

1035-483: A marked axial tilt of 82.23° with a retrograde rotation period of 17 hours and 14 minutes. This means that in an 84-Earth-year orbital period around the Sun, its poles get around 42 years of continuous sunlight, followed by 42 years of continuous darkness. Uranus has the third-largest diameter and fourth-largest mass among the Solar System's planets. Based on current models, inside its volatile mantle layer

1150-423: A much greater distance from Uranus are the ten known irregular moons . The planet's magnetosphere is highly asymmetric and has many charged particles , which may be the cause of the darkening of its rings and moons. Uranus is visible to the naked eye, but it is very dim and was not classified as a planet until 1781, when it was first observed by William Herschel . About seven decades after its discovery, consensus

1265-401: A particular vantage point, the transiting body appears to move across the face of the larger body, covering a small portion of it. The word "transit" refers to cases where the nearer object appears smaller than the more distant object. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations . However, the probability of seeing

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1380-522: A planet, expanding the known boundaries of the Solar System for the first time in history and making Uranus the first planet classified as such with the aid of a telescope . The discovery of Uranus also effectively doubled the size of the known Solar System because Uranus is around twice the distance from the Sun as the planet Saturn . Before its recognition as a planet, Uranus had been observed on numerous occasions, albeit generally misidentified as

1495-467: A polar cap in the northern hemisphere. So Uranus appeared to be asymmetric: bright near the south pole and uniformly dark in the region north of the southern collar. In 2007, when Uranus passed its equinox, the southern collar almost disappeared, and a faint northern collar emerged near 45° of latitude. In 2023, a team employing the Very Large Array observed a dark collar at 80° latitude, and

1610-422: A primary and its satellite . A large number of moons have been discovered analyzing the photometric light curves of small bodies and detecting a second, superimposed brightness variation, from which an orbital period for the satellite (secondary), and a secondary-to-primary diameter-ratio (for the binary system ) can often be derived. The Moon or another celestial body can occult multiple celestial bodies at

1725-497: 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." Although Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. Finnish-Swedish astronomer Anders Johan Lexell , working in Russia, was the first to compute the orbit of the new object. Its nearly circular orbit led him to

1840-477: A revolving oblate spheroid set at the point at which atmospheric pressure equals 1 bar (100 kPa) is conditionally designated as a "surface". It has equatorial and polar radii of 25,559 ± 4 km (15,881.6 ± 2.5 mi) and 24,973 ± 20 km (15,518 ± 12 mi), respectively. This surface is used throughout this article as a zero point for altitudes. Uranus's internal heat appears markedly lower than that of

1955-437: A southern companion telescope added in 2009. KELT North observes "26-degree wide strip of sky that is overhead from North America during the year", while KELT South observes single target areas of the size 26 by 26 degrees. Both telescopes can detect and identify transit events as small as a 1% flux dip, which allows for detection of planetary systems similar to those in our planetary system. The Kepler space telescope served

2070-462: A star in 1977. On 3 July 1989, Saturn passed in front of the 5th magnitude star 28 Sagittarii . Pluto occulted stars in 1988, 2002, and 2006, allowing its tenuous atmosphere to be studied via atmospheric limb sounding . In rare cases, one planet can pass in front of another. If the nearer planet appears larger than the more distant one, the event is called a mutual planetary occultation. The last occultation or transit occurred on 3 January 1818 and

2185-537: A star. The earliest possible known observation was by Hipparchus , who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy 's Almagest . The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri . The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769, including on four consecutive nights. William Herschel observed Uranus on 13 March 1781 from

2300-427: A total of 10 cloud features across the entire planet. One proposed explanation for this dearth of features is that Uranus's internal heat is markedly lower than that of the other giant planets, being the coldest planet in the Solar System. 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. Their boundary

2415-583: A transit is dependent on the point of observation, the Earth itself transits the Sun if observed from Mars. In the solar transit by the Moon captured during calibration of the STEREO B spacecraft's ultraviolet imaging, the Moon appears much smaller than it does when seen from Earth , because the spacecraft–Moon separation was several times greater than the Earth–Moon distance . The term can also be used to describe

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2530-403: A transit there are four "contacts", when the circumference of the small circle (small body disk) touches the circumference of the large circle (large body disk) at a single point . Historically, measuring the precise time of each point of contact was one of the most accurate ways to determine the positions of astronomical bodies. The contacts happen in the following order: A fifth named point

2645-510: A transiting planet is low because it is dependent on the alignment of the three objects in a nearly perfectly straight line. Many parameters of a planet and its parent star can be determined based on the transit. One type of transit involves the motion of a planet between a terrestrial observer and the Sun . This can happen only with inferior planets , namely Mercury and Venus (see transit of Mercury and transit of Venus ). However, because

2760-659: Is Dao Yurenat ( ดาวยูเรนัส ), as in English. Its other name in Thai is Dao Maruettayu ( ดาวมฤตยู , Star of Mṛtyu), after the Sanskrit word for 'death', Mrtyu ( मृत्यु ). In Mongolian , its name is Tengeriin Van ( Тэнгэрийн ван ), translated as 'King of the Sky', reflecting its namesake god's role as the ruler of the heavens. In Hawaiian , its name is Heleʻekala ,

2875-456: Is 5.68 with a standard deviation of 0.17, while the extremes are 5.38 and 6.03. This range of brightness is near the limit of naked eye visibility. Much of the variability is dependent upon the planetary latitudes being illuminated from the Sun and viewed from the Earth. 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. At opposition , Uranus

2990-462: Is a dynamic part of the atmosphere, exhibiting strong winds, bright clouds, and seasonal changes. The middle layer of the Uranian atmosphere is the stratosphere , where temperature generally increases with altitude from 53 K (−220 °C; −364 °F) in the tropopause to between 800 and 850 K (527 and 577 °C; 980 and 1,070 °F) at the base of the thermosphere. The heating of

3105-412: Is a limiting factor. In a 2021 study, the ice giants' interior conditions were mimicked by compressing water that contained minerals such as olivine and ferropericlase , thus showing that large amounts of magnesium could be dissolved in the liquid interiors of Uranus and Neptune. If Uranus has more of this magnesium than Neptune, it could form a thermal insulation layer, thus potentially explaining

3220-624: Is a rocky core, and surrounding it is a thick hydrogen and helium atmosphere. Trace amounts of hydrocarbons (thought to be produced via hydrolysis ) and carbon monoxide along with carbon dioxide (thought to have been originated from comets ) have been detected in the upper atmosphere. There are many unexplained climate phenomena in Uranus's atmosphere , such as its peak wind speed of 900 km/h (560 mph), variations in its polar cap, and its erratic cloud formation. The planet also has very low internal heat compared to other giant planets,

3335-411: Is a unique feature of Uranus. Its effects include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings. The Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus. Observations show that the ionosphere occupies altitudes from 2,000 to 10,000 km (1,200 to 6,200 mi). The Uranian ionosphere

3450-404: Is close to the protosolar helium mass fraction of 0.275 ± 0.01 , indicating that helium has not settled in its centre as it has in the gas giants. The third-most-abundant component of Uranus's atmosphere is methane ( CH 4 ). Methane has prominent absorption bands in the visible and near-infrared (IR), making Uranus aquamarine or cyan in colour. Methane molecules account for 2.3% of

3565-399: Is considered north and which is considered south and giving the planet prograde rotation. This gives it seasonal changes completely unlike those of the other planets. Pluto and asteroid 2 Pallas also have extreme axial tilts. Near the solstice , one pole faces the Sun continuously and the other faces away, with only a narrow strip around the equator experiencing a rapid day–night cycle, with

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3680-537: Is denser than that of either Saturn or Neptune, which may arise from the low concentration of hydrocarbons in the stratosphere. The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity . Auroral activity is insignificant as compared to Jupiter and Saturn. At ultraviolet and visible wavelengths, Uranus's atmosphere is bland in comparison to the other giant planets, even to Neptune, which it otherwise closely resembles. When Voyager 2 flew by Uranus in 1986, it observed

3795-444: Is located at about −45° of latitude . A narrow band straddling the latitudinal range from −45 to −50° is the brightest large feature on its visible surface. 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 1.3 to 2 bar. Besides the large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to

3910-520: Is nearly universal in astrology. In English-language popular culture , humour is often derived from the common pronunciation of Uranus's name, which resembles that of the phrase "your anus ". Uranus is called by a variety of names in other languages. Uranus's name is literally translated as the "sky king star" in Chinese ( 天王星 ; Tiānwángxīng ), Japanese (天王星), Korean (천왕성), and Vietnamese ( sao Thiên Vương ). In Thai , its official name

4025-404: Is not precisely known, because different figures emerge depending on the model chosen; it must be between 9.3 and 13.5 Earth masses. Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses. The remainder of the non-ice mass (0.5 to 3.7 Earth masses) is accounted for by rocky material . The standard model of Uranus's structure

4140-438: Is performed regularly by (primarily amateur) astronomers. Lunar occultations timed to an accuracy of a few tenths of a second have various scientific uses, particularly in refining our knowledge of lunar topography . Photoelectric analysis of lunar occultations have also discovered some stars to be very close visual or spectroscopic binaries . Some angular diameters of stars have been measured by timing of lunar occultations, which

4255-414: Is roughly 14.5 times that of Earth, making it the least massive of the giant planets. Its diameter is slightly larger than Neptune's at roughly four times that of Earth. A resulting density of 1.27 g/cm makes Uranus the second least dense planet, after Saturn. This value indicates that it is made primarily of various ices, such as water, ammonia, and methane. The total mass of ice in Uranus's interior

4370-429: Is similar at these altitudes. Heavier hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower. The abundance ratio of water is around 7 × 10 . Ethane and acetylene tend to condense in the colder lower part of the stratosphere and tropopause (below 10 mBar level) forming haze layers, which may be partly responsible for the bland appearance of Uranus. The concentration of hydrocarbons in

4485-411: Is sometimes called a water–ammonia ocean. The extreme pressure and temperature deep within Uranus may break up the methane molecules, with the carbon atoms condensing into crystals of diamond that rain down through the mantle like hailstones. This phenomenon is similar to diamond rains that are theorised by scientists to exist on Jupiter , Saturn , and Neptune . Very-high-pressure experiments at

4600-464: Is that it consists of three layers: a rocky ( silicate / iron–nickel ) core in the centre, an icy mantle in the middle, and an outer gaseous hydrogen/helium envelope. The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20% of the planet; the mantle comprises its bulk, with around 13.4 Earth masses, and the upper atmosphere is relatively insubstantial, weighing about 0.5 Earth masses and extending for

4715-628: Is that of greatest transit, when the apparent centers of the two bodies are nearest to each other, halfway through the transit. Since transit photometry allows for scanning large celestial areas with a simple procedure, it has been the most popular and successful form of finding exoplanets in the past decade and includes many projects, some of which have already been retired, others in use today, and some in progress of being planned and created. The most successful projects include HATNet, KELT, Kepler, and WASP, and some new and developmental stage missions such as TESS , HATPI, and others which can be found among

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4830-400: Is that, averaged over the Uranian year, the near-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 that causes this is unknown. The reason for Uranus's unusual axial tilt is also not known with certainty, but the usual speculation is that during the formation of

4945-459: Is the leading form of exoplanet discovery . As an exoplanet moves in front of its host star there is a dimming in the luminosity of the host star that can be measured. Larger planets make the dip in luminosity more noticeable and easier to detect. Followup observations using other methods are often carried out to ensure it is a planet. There are currently (December 2018) 2345 planets confirmed with Kepler light curves for stellar host. During

5060-420: Is the seventh planet from the Sun . It is a gaseous cyan -coloured ice giant . Most of the planet is made of water , ammonia , and methane in a supercritical phase of matter , which astronomy calls "ice" or volatiles . The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature (49 K (−224 °C; −371 °F)) of all the Solar System 's planets. It has

5175-436: Is thought to have 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 (0.3 and 1 MPa) and finally directly detected thin methane clouds at 1 to 2 bar (0.1 to 0.2 MPa). The troposphere

5290-412: Is useful for determining effective temperatures of those stars. Early radio astronomers found occultations of radio sources by the Moon valuable for determining their exact positions, because the long wavelength of radio waves limited the resolution available through direct observation. This was crucial for the unambiguous identification of the radio source 3C 273 with the optical quasar and its jet, and

5405-435: Is visible to the naked eye in dark skies, and becomes an easy target even in urban conditions with binoculars. On larger amateur telescopes with an objective diameter of between 15 and 23 cm, Uranus 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. Uranus's mass

5520-546: The International Astronomical Union definition that the north pole is the pole which lies on Earth's North's side of the invariable plane of the Solar System . Uranus has retrograde rotation when defined this way. Alternatively, the convention in which a body's north and south poles are defined according to the right-hand rule in relation to the direction of rotation, Uranus's axial tilt may be given instead as 97.8°, which reverses which pole

5635-507: The Lawrence Livermore National Laboratory suggest that an ocean of metallic liquid carbon, perhaps with floating solid 'diamond-bergs', may comprise the base of the mantle. The bulk compositions of Uranus and Neptune are different from those of Jupiter and Saturn , with ice dominating over gases, hence justifying their separate classification as ice giants . There may be a layer of ionic water where

5750-651: The List of Exoplanet Search Projects . HATNet Project is a set of northern telescopes in Fred Lawrence Whipple Observatory , Arizona and Mauna Kea Observatories , HI, and southern telescopes around the globe, in Africa, Australia, and South America, under the HATSouth branch of the project. These are small aperture telescopes, just like KELT, and look at a wide field which allows them to scan

5865-445: The Moon passes in front of a star during the course of its orbital motion around the Earth. Since the Moon, with an angular speed with respect to the stars of 0.55 arcsec /s or 2.7 μrad/s, has a very thin atmosphere and stars have an angular diameter of at most 0.057 arcseconds or 0.28 μrad, a star that is occulted by the Moon will disappear or reappear in 0.1 seconds or less on the Moon's edge, or limb. Events that take place on

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5980-458: The Starshade , which uses a sunflower -shaped coronagraph disc. A comparable proposal was also made for a satellite to occult bright X-ray sources, called an X-ray Occulting Steerable Satellite or XOSS. Transit (astronomy) In astronomy , a transit (or astronomical transit ) is the passage of a celestial body directly between a larger body and the observer. As viewed from

6095-497: The auroral activity can provide the necessary energy to maintain these temperatures. The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0.1 mBar pressure levels may contribute too. In addition to molecular hydrogen, the thermosphere-corona contains many free hydrogen atoms. Their small mass and high temperatures explain why the corona extends as far as 50,000 km (31,000 mi), or two Uranian radii, from its surface. This extended corona

6210-456: The "Georgian Planet" in honour of his new patron, King George III. He explained this decision in a letter to Joseph Banks: In the fabulous ages of ancient times the appellations of Mercury, Venus, Mars, Jupiter and Saturn were given to the Planets, as being the names of their principal heroes and divinities. In the present more philosophical era it would hardly be allowable to have recourse to

6325-551: The Earth-sized impactor theorised to be behind Uranus's axial tilt left the planet with a depleted core temperature, as the impact caused Uranus to expel most of its primordial heat. Another hypothesis is that some form of barrier exists in Uranus's upper layers that prevents the core's heat from reaching the surface. For example, convection may take place in a set of compositionally different layers, which may inhibit upward heat transport ; perhaps double diffusive convection

6440-455: The Hawaiian rendering of the name 'Herschel'. In Māori , its name is Whērangi . It is argued that the differences between the ice giants and the gas giants arise from their formation history. The Solar System is hypothesised to have formed from a rotating disk of gas and dust known as the presolar nebula . Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, and

6555-522: The Kepler mission between 7 March 2009 and 11 May 2013, where it observed one part of the sky in search of transiting planets within a 115 square degrees of the sky around the Cygnus , Lyra , and Draco constellations. After that, the satellite continued operating until 15 November 2018, this time changing its field along the ecliptic to a new area roughly every 75 days due to reaction wheel failure. TESS

6670-654: The Latinised form of the deity's name, and the Roman equivalent was Caelus. In 1789, Bode's Royal Academy colleague Martin Klaproth named his newly discovered element uranium in support of Bode's choice. Ultimately, Bode's suggestion became the most widely used, and became universal in 1850 when HM Nautical Almanac Office , the final holdout, switched from using Georgium Sidus to Uranus . Uranus has two astronomical symbols . The first to be proposed, [REDACTED] ,

6785-467: The Moon or by planets. Occultations of Aldebaran are in this epoch only possible by the Moon, because the planets pass Aldebaran to the north. Neither planetary nor lunar occultations of Pollux are currently possible, however several thousand years ago lunar occultations were possible. Some notably close deep-sky objects , such as the Pleiades , can be occulted by the Moon. Within a few kilometres of

6900-452: The Moon's dark limb are of particular interest to observers, because the lack of glare allows easier observation and timing. The Moon's orbit is inclined slightly with respect to the ecliptic (see orbit of the Moon ) meaning any star with an ecliptic latitude between –6.6 and +6.6 degrees may be occulted by it. Three first magnitude stars appear well within that band – Regulus , Spica , and Antares – meaning they may be occulted by

7015-429: The Solar System, an Earth-sized protoplanet collided with Uranus, causing the skewed orientation. Research by Jacob Kegerreis of Durham University suggests that the tilt resulted from a rock larger than Earth crashing into the planet 3 to 4 billion years ago. Uranus's south pole was pointed almost directly at the Sun at the time of Voyager 2 's flyby in 1986. The mean apparent magnitude of Uranus

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7130-421: The Sun low over the horizon. On the other side of Uranus's 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. 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. One result of this axis orientation

7245-411: The Sun, marking the first time a planetary transit has been observed from a celestial body besides Earth. In rare cases, one planet can pass in front of another. If the nearer planet appears smaller than the more distant one, the event is called a mutual planetary transit . The transit method can be used to discover exoplanets . As a planet eclipses/transits its host star it will block a portion of

7360-400: The Uranian stratosphere above the haze is significantly lower than in the stratospheres of the other giant planets. The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature of around 800 K (527 °C) to 850 K (577 °C). The heat sources necessary to sustain such a high level are not understood, as neither the solar UV nor

7475-482: The ancient Greek deity of the sky Uranus ( Ancient Greek : Οὐρανός ), known as Caelus in Roman mythology, the father of Cronus ( Saturn ), grandfather of Zeus ( Jupiter ) and the great-grandfather of Ares ( Mars ), which was rendered as Uranus in Latin ( IPA: [ˈuːranʊs] ). It is the only one of the eight planets whose English name derives from a figure of Greek mythology . The pronunciation of

7590-463: 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 mixing ratio 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. The abundances of less volatile compounds such as ammonia, water, and hydrogen sulfide in

7705-453: The cause of which remains unclear. Like the other giant planets, Uranus has a ring system , a magnetosphere , and many natural satellites . The extremely dark ring system reflects only about 2% of the incoming light. Uranus's 28 natural satellites include 18 known regular moons , of which 13 are small inner moons . Further out are the larger five major moons of the planet: Miranda , Ariel , Umbriel , Titania , and Oberon . Orbiting at

7820-463: The coldest upper region of the troposphere (the tropopause ) actually vary in the range between 49 and 57 K (−224 and −216 °C; −371 and −357 °F) depending on planetary latitude. The tropopause region is responsible for the vast majority of Uranus's thermal far infrared emissions, thus determining its effective temperature of 59.1 ± 0.3 K (−214.1 ± 0.3 °C; −353.3 ± 0.5 °F). The troposphere

7935-471: The conclusion that it was a planet rather than a comet. 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". Bode concluded that its near-circular orbit was more like a planet's than a comet's. The object was soon universally accepted as a new planet. By 1783, Herschel acknowledged this to Royal Society president Joseph Banks : "By

8050-544: The course of the American Revolutionary War by calling the new planet either Neptune George III or Neptune Great Britain , a compromise Lexell suggested as well. Daniel Bernoulli suggested Hypercronius and Transaturnis . Minerva was also proposed. In a March 1782 treatise, Johann Elert Bode proposed Uranus , the Latinised version of the Greek god of the sky, Ouranos . Bode argued that

8165-559: The deep atmosphere are poorly known. They are probably also higher than solar values. Along with 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. They include ethane ( C 2 H 6 ), acetylene ( C 2 H 2 ), methylacetylene ( CH 3 C 2 H ), and diacetylene ( C 2 HC 2 H ). Spectroscopy has also uncovered traces of water vapour, carbon monoxide , and carbon dioxide in

8280-423: The direction of rotation. At some latitudes, such as about 60 degrees south, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours. The Uranian axis of rotation is approximately parallel to the plane of the Solar System, with an axial tilt of 82.23°. Depending on which pole is considered north, the tilt can be described either as 82.23° or as 97.8°. The former follows

8395-412: 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 on to the nebula's leftover gas. 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

8510-446: The edge of an occultation's predicted path, referred to as its northern or southern limit, an observer may see the star intermittently disappearing and reappearing as the irregular limb of the Moon moves past the star, creating what is known as a grazing lunar occultation . From an observational and scientific standpoint, these "grazes" are the most dynamic and interesting of lunar occultations. The accurate timing of lunar occultations

8625-538: The garden of his house at 19 New King Street in Bath, Somerset , England (now the Herschel Museum of Astronomy ), and initially reported it (on 26 April 1781) as a comet . With a homemade 6.2-inch reflecting telescope, Herschel "engaged in a series of observations on the parallax of the fixed stars." Herschel recorded in his journal: "In the quartile near ζ Tauri  ... either [a] Nebulous star or perhaps

8740-488: The gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On 23 September 1846, Johann Gottfried Galle located a new planet, later named Neptune , at nearly the position predicted by Le Verrier. The rotational period of the interior of Uranus is 17 hours, 14 minutes. As on all giant planets , its upper atmosphere experiences strong winds in

8855-422: 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 a scientific determination of which model is correct. The fluid interior structure of Uranus means that it has no solid surface. The gaseous atmosphere gradually transitions into the internal liquid layers. For the sake of convenience,

8970-410: The last 20% of Uranus's radius. Uranus's core density is around 9 g/cm , with a pressure in the centre of 8 million  bars (800 GPa ) and a temperature of about 5000  K . 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 . This fluid, which has a high electrical conductivity,

9085-463: The light from the star. If the planet transits in-between the star and the observer the change in light can be measured to construct a light curve . Light curves are measured with a charge-coupled device . The light curve of a star can disclose several physical characteristics of the planet and star, such as density. Multiple transit events must be measured to determine the characteristics which tend to occur at regular intervals. Multiple planets orbiting

9200-410: The low probability of a transit in any specific system, large selections of the sky must be regularly observed in order to see a transit. Hot Jupiters are more likely to be seen because of their larger radius and short semi-major axis. In order to find Earth-sized planets, red dwarf stars are observed because of their small radius. Even though transiting has a low probability it has proven itself to be

9315-530: The motion of a satellite across its parent planet, for instance one of the Galilean satellites ( Io , Europa , Ganymede , Callisto ) across Jupiter , as seen from Earth . Although rare, cases where four bodies are lined up do happen. One of these events occurred on 27 June 1586, when Mercury transited the Sun as seen from Venus at the same time as a transit of Mercury from Saturn and a transit of Venus from Saturn. No missions were planned to coincide with

9430-481: The name Uranus preferred among astronomers is / ˈ jʊər ə n ə s / YOOR -ə-nəs , with the long "u" of English and stress on the first syllable as in Latin Uranus , in contrast to / j ʊ ˈ r eɪ n ə s / yoo- RAY -nəs , with stress on the second syllable and a long a , though both are considered acceptable. Consensus on the name was not reached until almost 70 years after

9545-458: The name should follow the mythology so as not to stand out as different from the other planets, and that Uranus was an appropriate name as the father of the first generation of the Titans . He also noted the elegance of the name in that just as Saturn was the father of Jupiter , the new planet should be named after the father of Saturn. However, he was apparently unaware that Uranus was only

9660-497: The names Astraea , Cybele (now the names of asteroids), and Neptune , which would become the name of the next planet to be discovered. Georg Lichtenberg from Göttingen also supported Astraea (as Austräa ), but she is traditionally associated with Virgo instead of Taurus. Neptune was supported by other astronomers who liked the idea of commemorating the victories of the British Royal Naval fleet in

9775-528: The next will occur on 22 November 2065, in both cases involving the same two planets— Venus and Jupiter . Jupiter rarely occults Saturn . This is one of the rarest events known, with the next occurrence on February 10, 7541. This event is visible worldwide since the duo would be positioned almost in opposition to the sun, in the border line between the constellations of Orion and Taurus . In some areas this occultation cannot be seen, but when viewed through even small telescopes, both gas giants appear to be in

9890-452: The nominal surface, which is defined to lie at a pressure of 1 bar. The Uranian atmosphere can be divided into three layers: the troposphere , between altitudes of −300 and 50 km (−186 and 31 mi) and pressures from 100 to 0.1 bar (10 MPa to 10 kPa); the stratosphere , spanning altitudes between 50 and 4,000 km (31 and 2,485 mi) and pressures of between 0.1 and 10  bar (10 kPa to 10  μPa ); and

10005-478: The north from the collar. In all other respects, Uranus looked like a dynamically dead planet in 1986. Voyager 2 arrived during the height of Uranus's southern summer and could not observe the northern hemisphere. At the beginning of the 21st century, when the northern polar region came into view, the Hubble Space Telescope (HST) and Keck telescope initially observed neither a collar nor

10120-620: 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." In recognition of his achievement, King George III gave Herschel an annual stipend of £200 (equivalent to £30,000 in 2023) on condition that he moved to Windsor so that the Royal Family could look through his telescopes. The name Uranus references

10235-466: The orbiting planets to be observed. The proposed satellite would have a dimension of 70 by 70 metres (230 ft × 230 ft), a mass of about 600 kg, and maneuver by means of an ion drive engine in combination with using the sheet as a light sail. Positioned at a distance of 100,000 km from the telescope, it would block more than 99.998% of the starlight. There are two possible configurations of this satellite. The first would work with

10350-413: The other giant planets; in astronomical terms, it has a low thermal flux . Why Uranus's internal temperature is so low is still not understood. Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun, but Uranus radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of

10465-400: The planet's discovery. During the original discussions following discovery, Maskelyne asked Herschel to "do the astronomical world the faver [ sic ] to give a name to your planet, which is entirely your own, [and] which we are so much obliged to you for the discovery of". In response to Maskelyne's request, Herschel decided to name the object Georgium Sidus (George's Star), or

10580-507: The planet's disk partly blocked by the slowly moving Moon. The same mechanism can be seen with the Sun, where observers on Earth will view it as a solar eclipse . Therefore, a total solar eclipse is essentially the Moon occulting the Sun. Stars may also be occulted by planets. Occultations of bright stars are rare. In 1959, Venus occulted Regulus , and the next occultation of a bright star (also Regulus by Venus) will be in 2044. Uranus 's rings were first discovered when that planet occulted

10695-512: The planet's low temperature. Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope that is accessible to remote sensing is called its atmosphere . 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 (47 °C; 116 °F). The tenuous thermosphere extends over two planetary radii from

10810-546: The point of its discovery northeast of the binary star Zeta Tauri twice—in March 1865 and March 1949—and will return to this location again in April 2033. Its average distance from the Sun is roughly 20  AU (3  billion   km ; 2 billion  mi ). The difference between its minimum and maximum distance from the Sun is 1.8 AU, larger than that of any other planet, though not as large as that of dwarf planet Pluto . The intensity of sunlight varies inversely with

10925-408: The powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while

11040-475: The proposed Uranus Orbiter and Probe mission a top priority in the 2023–2032 survey, and the CNSA 's proposal to fly by the planet with a subprobe of Tianwen-4 . Like the classical planets , Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit. William Herschel first observed Uranus on 13 March 1781, leading to its discovery as

11155-402: The same host star can cause transit-timing variations (TTV). TTV is caused by the gravitational forces of all orbiting bodies acting upon each other. The probability of seeing a transit from Earth is low, however. The probability is given by the following equation. where R star and R planet are the radius of the star and planet, respectively, and a is the semi-major axis. Because of

11270-671: The same method and call it Juno, Pallas, Apollo or Minerva, for a name to our new heavenly body. The first consideration of any particular event, or remarkable incident, seems to be its chronology: if in any future age it should be asked, when this last-found Planet was discovered? It would be a very satisfactory answer to say, 'In the reign of King George the Third'. Herschel's proposed name was not popular outside Britain and Hanover, and alternatives were soon proposed. Astronomer Jérôme Lalande proposed that it be named Herschel in honour of its discoverer. Swedish astronomer Erik Prosperin proposed

11385-409: The same part of view through the eyepiece. The last one occurred in 6857 B.C.E. A further set of occultations are those when a small Solar System body or dwarf planet passes in front of a star, temporarily blocking its light as seen from Earth. These occultations are useful for measuring the size and position of body much more precisely than can be done by other means. A cross-sectional profile of

11500-505: The same time. Because of its relatively large angular diameter the Moon, at any given time, occults an indeterminate number of stars and galaxies. However the Moon occulting (obscuring) two bright objects (e.g. two planets or a bright star and a planet) simultaneously is extremely rare and can be seen only from a small part of the world: the last such event was on 23 April 1998 when it occulted Venus and Jupiter for observers on Ascension Island . The Big Occulting Steerable Satellite (BOSS)

11615-432: The shape of a body can even be determined if a number of observers at different, nearby, locations observe the occultation. Occultations have been used to calculate the diameter of trans-Neptunian objects such as 2002 TX 300 , Ixion and Varuna . Software for coordinating observations is available for download at http://www.occultwatcher.net/ In addition, mutual occultation and eclipsing events can occur between

11730-399: The southern hemisphere the bright collar masks them—was shown to be incorrect. Nevertheless, there are differences between the clouds of each hemisphere. The northern clouds are smaller, sharper and brighter. They appear to lie at a higher altitude. The lifetime of clouds spans several orders of magnitude. Some small clouds live for hours; at least one southern cloud may have persisted since

11845-441: The spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere . Uranus's heat flux is only 0.042 ± 0.047  W / m , which is lower than the internal heat flux of Earth of about 0.075  W / m . The lowest temperature recorded in Uranus's tropopause is 49 K (−224.2 °C; −371.5 °F), making Uranus the coldest planet in the Solar System. One of the hypotheses for this discrepancy suggests

11960-408: The square of the distance—on Uranus (at about 20 times the distance from the Sun compared to Earth), it is about 1/400 the intensity of light on Earth. The orbital elements of Uranus were first calculated in 1783 by Pierre-Simon Laplace . With time, discrepancies began to appear between predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to

12075-501: The stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed. Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this flummoxed reply from him on 23 April 1781: "I don't know what to call it. It is as likely to be

12190-651: The stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons , which form in this part of the atmosphere as a result of methane photolysis . Heat is also conducted from the hot thermosphere. The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding to a pressure range of 1,000 to 10 Pa and temperatures of between 75 and 170 K (−198 and −103 °C; −325 and −154 °F). The most abundant hydrocarbons are methane, acetylene , and ethane with mixing ratios of around 10 relative to hydrogen. The mixing ratio of carbon monoxide

12305-423: The symbols for the other planets while remaining distinct. This symbol predominates in modern astronomical use in the rare cases that symbols are used at all. The second symbol, [REDACTED] , was 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 surname"). The second symbol

12420-436: The thermosphere extending from 4,000 km to as high as 50,000 km from the surface. There is no mesosphere . The composition of Uranus's atmosphere is different from its bulk, consisting mainly of molecular hydrogen and helium. The helium molar fraction , i.e. the number of helium atoms per molecule of gas, is 0.15 ± 0.03 in the upper troposphere, which corresponds to a mass fraction 0.26 ± 0.05 . This value

12535-578: The transit of Earth visible from Mars on 11 May 1984 and the Viking missions had been terminated a year previously. Consequently, the next opportunity to observe such an alignment will be in 2084. On 21 December 2012, the Cassini–Huygens probe, in orbit around Saturn , observed the planet Venus transiting the Sun. On 3 June 2014, the Mars rover Curiosity observed the planet Mercury transiting

12650-447: The upper atmosphere, which can only originate from an external source such as infalling dust and comets . The troposphere is the lowest and densest part of the atmosphere and is characterised by a decrease in temperature with altitude. The temperature falls from about 320 K (47 °C; 116 °F) at the base of the nominal troposphere at −300 km to 53 K (−220 °C; −364 °F) at 50 km. The temperatures in

12765-402: The water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions move freely within the oxygen lattice. Although the model considered above is reasonably standard, it is not unique; other models also satisfy observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in

12880-407: Was a proposed satellite that would work in conjunction with a telescope to detect planets around distant stars. The satellite consists of a large, very lightweight sheet, and a set of maneuvering thrusters and navigation systems. It would maneuver to a position along the line of sight between the telescope and a nearby star. The satellite would thereby block the radiation from the star, permitting

12995-423: Was launched on 18 April 2018, and is planned to survey most of the sky by observing it strips defined along the right ascension lines for 27 days each. Each area surveyed is 27 by 90 degrees. Because of the positioning of sections, the area near TESS's rotational axis will be surveyed for up to 1 year, allowing for the identification of planetary systems with longer orbital periods. Uranus Uranus

13110-464: Was proposed by Johann Gottfried Köhler at Bode's request in 1782. Köhler suggested that the new planet be given the symbol for platinum , which had been described scientifically only 30 years before. As there was no alchemical symbol for platinum, he suggested ⛢ or ⛢ , a combination of the planetary-metal symbols ☉ (gold) and ♂ (iron), as platinum (or 'white gold') is found mixed with iron. Bode thought that an upright orientation, ⛢, fit better with

13225-452: Was reached that the planet be named after the Greek god Uranus (Ouranos), one of the Greek primordial deities . As of 2024, it had been visited up close only once when in 1986 the Voyager 2 probe flew by the planet. Though nowadays it can be resolved and observed by telescopes, there is much desire to revisit the planet, as shown by Planetary Science Decadal Survey 's decision to make

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