Global InformationUranus information
 Uranus in true colour,[a] as captured by Voyager 2. Uranus's pale, muted appearance is due to a shroud of haze above its clouds | |||||||||||||
| Discovery | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Discovered by | William Herschel | ||||||||||||
| Discovery date | 13 March 1781 | ||||||||||||
| Designations | |||||||||||||
| Pronunciation | /ˈjʊərənəs/ ⓘ[1] or /jʊˈreɪnəs/ ⓘ[2] | ||||||||||||
Named after | the Latin form Ūranus of the Greek god Οὐρανός Ouranos | ||||||||||||
| Adjectives | Uranian (/jʊˈreɪniən/)[3] | ||||||||||||
| Symbol |  (mostly astronomical), (mostly astrological) | ||||||||||||
| Orbital characteristics[4][b] | |||||||||||||
| Epoch J2000 | |||||||||||||
| Aphelion | 20.0965 AU (3.00639 billion km) | ||||||||||||
| Perihelion | 18.2861 AU (2.73556 billion km) | ||||||||||||
Semi-major axis | 19.19126 AU (2.870972 billion km) | ||||||||||||
| Eccentricity | 0.04717 | ||||||||||||
Orbital period (sidereal) |
| ||||||||||||
Orbital period (synodic) | 369.66 days[7] | ||||||||||||
Average orbital speed | 6.80 km/s[7] | ||||||||||||
Mean anomaly | 142.238600° | ||||||||||||
| Inclination |
| ||||||||||||
Longitude of ascending node | 74.006° | ||||||||||||
Time of perihelion | 17–19 August 2050[9][10] | ||||||||||||
Argument of perihelion | 96.998857° | ||||||||||||
| Known satellites | 28 | ||||||||||||
| Physical characteristics | |||||||||||||
Mean radius | 25,362±7 km[11][c] | ||||||||||||
Equatorial radius | 25,559±4 km 4.007 Earths[11][c] | ||||||||||||
Polar radius | 24,973±20 km 3.929 Earths[11][c] | ||||||||||||
| Flattening | 0.0229±0.0008[d] | ||||||||||||
| Circumference | 159,354.1 km[5] | ||||||||||||
Surface area | 8.1156×109 km2[5][c] 15.91 Earths | ||||||||||||
| Volume | 6.833×1013 km3[7][c] 63.086 Earths | ||||||||||||
| Mass | (8.6810±0.0013)×1025 kg 14.536 Earths[12] GM=5,793,939±13 km3/s2 | ||||||||||||
Mean density | 1.27 g/cm3[7][e] | ||||||||||||
Surface gravity | 8.69 m/s2[7][c] 0.886 g | ||||||||||||
Moment of inertia factor | 0.23[13] (estimate) | ||||||||||||
Escape velocity | 21.3 km/s[7][c] | ||||||||||||
Synodic rotation period | −0.71832 d −17 h 14 m 23 s (retrograde)[6] | ||||||||||||
Sidereal rotation period | −0.71833 d −17 h 14 min 24 s (retrograde)[11] | ||||||||||||
Equatorial rotation velocity | 2.59 km/s 9,320 km/h | ||||||||||||
Axial tilt | 82.23° (to orbit, retrograde). [7] 97.77°(prograde, right-hand rule) | ||||||||||||
North pole right ascension | 17h 9m 15s 257.311°[11] | ||||||||||||
North pole declination | −15.175°[11] | ||||||||||||
| Albedo | 0.300 (Bond)[14] 0.488 (geom.)[15] | ||||||||||||
| |||||||||||||
Apparent magnitude | 5.38[18] to 6.03[18] | ||||||||||||
Absolute magnitude (H) | −7.2[19] | ||||||||||||
Angular diameter | 3.3″ to 4.1″[7] | ||||||||||||
| Atmosphere[17][20][21][f] | |||||||||||||
Scale height | 27.7 km[7] | ||||||||||||
| Composition by volume | Below 1.3 bar (130 kPa):
| ||||||||||||
Uranus 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 in astronomy is called 'ice' or volatiles. The planet's atmosphere has a complex layered cloud structure and has the lowest minimum temperature of 49 K (−224 °C; −371 °F) out of all the Solar System's planets. It has 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 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),[22] variations in its polar cap, and its erratic cloud formation. The planet also has very low internal heat compared to other giant planets, the cause of which remains unclear.
Like the other giant planets, Uranus has a ring system, a magnetosphere, and many natural satellites. Its ring system is extremely dark, with only about 2% of the incoming light reflected. 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 a much greater distance from Uranus are the nine 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 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.[23] 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 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.[24]
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OEDwas invoked but never defined (see the help page). - ^ "Uranian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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Souami_Souchay_2012was invoked but never defined (see the help page). - ^ Jean Meeus, Astronomical Algorithms (Richmond, Virginia: Willmann-Bell, 1998) p271. Bretagnon's complete VSOP87 model. It gives the 17th @ 18.283075301au. http://vo.imcce.fr/webservices/miriade/?forms Archived 7 September 2021 at the Wayback Machine IMCCE Observatoire de Paris / CNRS Calculated for a series of dates, five or ten days apart, in August 2050, using an interpolation formula from Astronomical Algorithms. Perihelion came very early on the 17th. INPOP planetary theory
- ^ "HORIZONS Planet-center Batch call for August 2050 Perihelion". ssd.jpl.nasa.gov (Perihelion for Uranus planet-center (799) occurs on 2050-Aug-19 at 18.28307512au during a rdot flip from negative to positive). NASA/JPL. Archived from the original on 7 September 2021. Retrieved 7 September 2021.
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Jacobson Campbell et al. 1992was invoked but never defined (see the help page). - ^ de Pater, Imke; Lissauer, Jack J. (2015). Planetary Sciences (2nd updated ed.). New York: Cambridge University Press. p. 250. ISBN 978-0521853712. Archived from the original on 26 November 2016. Retrieved 17 August 2016.
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Mallama_and_Hiltonwas invoked but never defined (see the help page). - ^ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on 24 July 2023. Retrieved 29 May 2023.
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Conrath Gautier et al. 1987was invoked but never defined (see the help page). - ^ Cite error: The named reference
Sromovsky & Fry 2005was invoked but never defined (see the help page). - ^ "Exploration | Uranus". NASA Solar System Exploration. Archived from the original on 7 August 2020. Retrieved 8 February 2020.
Jan. 24, 1986: NASA's Voyager 2 made the first - and so far the only - visit to Uranus.
- ^ Jones, Andrew (21 December 2023). "China's plans for outer Solar System exploration". The Planetary Society. Archived from the original on 31 December 2023. Retrieved 24 January 2024.