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This article is about the planet. For other uses, see Uranus (disambiguation).
Uranus
Uranus presented a nearly featureless disk to Voyager 2
Discovery
Discovered by William Herschel
Discovery date March 13, 1781
Designations
Pronunciation i /ˈj ərənəs/ or i /jʊˈre
ʊ ɪnəs/[1][2]
Adjective Uranian
Orbital characteristics[3][a]
Epoch J2000
Aphelion 3,004,419,704 km
20.083 305 26 AU
Perihelion 2,748,938,461 km
18.375 518 63 AU
Semi-major axis 2,876,679,082 km
19.229 411 95 AU
Eccentricity 0.044 405 586
Orbital period 30,799.095 days
84.323 326 yr
42,718 Uranus solar days[4]
Synodic period 369.66 days[5]
Average orbital speed 6.81 km/s[5]
Mean anomaly 142.955 717°
Inclination 0.772 556° to Ecliptic
6.48° to Sun's equator
1.02° to Invariable plane[6]
Longitude of ascending node 73.989 821°
Argument of perihelion 96.541 318°
Satellites 27
Physical characteristics
Equatorial radius 25,559 ± 4 km
4.007 Earths[7][c]
Polar radius 24,973 ± 20 km
3.929 Earths[7][c]
Flattening 0.022 9 ± 0.000 8[b]
Circumference 156,909.98 km[citation needed]
Surface area 8.115 6×109 km2[8][c]
15.91 Earths
Volume 6.833×1013 km3[5][c]
63.086 Earths
Mass (8.6810 ± 0.0013)×1025 kg
14.536 Earths[9]
GM=5 793 939 ± 13 km3/s2
Mean density 1.27 g/cm3[5][c]
Equatorial surface gravity 8.69 m/s2[5][c]
0.886 g
Escape velocity 21.3 km/s[5][c]
Sidereal rotation
periodˈ–0.718 33 day
17 h 14 min 24 s[7]

2. Equatorial rotation velocity 2.59 km/s
9,320 km/h
Axial tilt 97.77°[7]
North pole right ascension 17 h 9 min 15 s
257.311°[7]
North pole declinationˈ–15.175°[7]
Albedo 0.300 (Bond)
0.51 (geom.)[5]
Surface temp.
1 bar level[11]
0.1 bar
(tropopause)[12]
min mean max
76 K
49 K 53 K 57 K
Apparent magnitude 5.9[10] to 5.32[5]
Angular diameterˈ3.3"–4.1"[5]
Atmosphere[12][13][14][d]
Scale height 27.7 km[5]
Composition (Below 1.3 bar)
83 ± 3% Hydrogen (H2)
15 ± 3% Helium
2.3% Methane
0.009%
(0.007–0.015%)ˈHydrogen deuteride (HD)[15]
Ices:
Ammonia
water
ammonium hydrosulfide (NH4SH)
methane (CH4)
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass
Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giant
Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian syste
Contents [hide]
1 History
1.1 Discovery
1.2 Naming
1.3 Nomenclature
2 Orbit and rotation
2.1 Axial tilt
2.2 Visibility
3 Internal structure
3.1 Internal heat
4 Atmosphere
4.1 Composition
4.2 Troposphere
4.3 Upper atmosphere
5 Planetary rings
6 Magnetic field
7 Climate
7.1 Banded structure, winds and clouds
7.2 Seasonal variation
8 Formation
9 Moons
10 Exploration

3. 11 In culture
12 See also
13 Notes
14 References
15 Further reading
16 External links
History
Discovery
Uranus had been observed on many occasions before its discovery as a planet, but it was generally mistaken for a s
Sir William Herschel observed the planet on March 13, 1781 while in the garden of his house at 19 New King Street
He recorded in his journal "In the quartile near ζ Tauri … either [a] Nebulous star or perhaps a comet".[23] On March
―ˈThe power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed s
Replica of the telescope used by Herschel to discover Uranus (William Herschel Museum, Bath)
Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from h
While Herschel continued to cautiously describe his new object as a comet, other astronomers had already begun to
The object was soon universally accepted as a new planet. By 1783, Herschel himself acknowledged this fact to Roy
Naming
Maskelyne asked Herschel to "do the astronomical world the faver [sic] to give a name to your planet, which is entire
William Herschel, discoverer of Uranus
―ˈIn the fabulous ages of ancient times the appellations of Mercury, Venus, Mars, Jupiter and Saturn were given to
Herschel's proposed name was not popular outside of Britain, and alternatives were soon proposed. Astronomer Jér
Nomenclature
The pronunciation of the name Uranus preferred among astronomers is /ˈj ərənəs/,[2][38] with stress on the first sy
ʊ
Uranus is the only planet whose name is derived from a figure from Greek mythology rather than Roman mythology:
Orbit and rotation
A 1998 false-colour near-infrared image of Uranus showing cloud bands, rings, and moons obtained by the Hubble S
Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km
The rotational period of the interior of Uranus is 17 hours, 14 minutes. As on all giant planets, its upper atmosphere e
Axial tilt
Uranus has an axial tilt of 97.77 degrees, so its axis of rotation is approximately parallel with the plane of the Solar S
Northern hemisphere Year Southern hemisphere
Winter solstice 1902, 1986 Summer solstice
Vernal equinox 1923, 2007 Autumnal equinox
Summer solstice 1944, 2028 Winter solstice
Autumnal equinox 1965, 2049 Vernal equinox
One result of this axis orientation is that, on average during the year, the polar regions of Uranus receive a greater e
Visibility
From 1995 to 2006, Uranus's apparent magnitude fluctuated between +5.6 and +5.9, placing it just within the limit of
Internal structure
Size comparison of Earth and Uranus
Diagram of the interior of Uranus
Uranus's mass is roughly 14.5 times that of the Earth, making it the least massive of the giant planets. Its diameter is

4. The standard model of Uranus's structure is that it consists of three layers: a rocky (silicate/iron-nickel) core in the ce
While the model considered above is reasonably standard, it is not unique; other models also satisfy observations. F
Internal heat
Uranus's internal heat appears markedly lower than that of the other giant planets; in astronomical terms, it has a low
One of the hypotheses for this discrepancy suggests that when Uranus was hit by a supermassive impactor, which c
Atmosphere
Main article: Atmosphere of Uranus
Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous enve
Composition
The composition of the Uranian atmosphere is different from the rest of the planet, consisting as it does mainly of mo
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 temperatur
The troposphere is believed to possess a highly complex cloud structure; water clouds are hypothesised to lie in the
Upper atmosphere
The middle layer of the Uranian atmosphere is the stratosphere, where temperature generally increases with altitude
The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature a
Planetary rings
Main article: Rings of Uranus
Uranus's inner rings. The bright outer ring is the ε ring; eight other rings are present.
The Uranian ring system
Uranus has a complicated planetary ring system, which was the second such system to be discovered in the Solar S
William Herschel described a possible ring around Uranus in 1789. This sighting is generally considered doubtful, as
In December 2005, the Hubble Space Telescope detected a pair of previously unknown rings. The largest is located
Magnetic field
The magnetic field of Uranus as observed by Voyager 2 in 1986. S and N are magnetic south and north poles.
Before the arrival of Voyager 2, no measurements of the Uranian magnetosphere had been taken, so its nature rem
Voyager's observations revealed that the magnetic field is peculiar, both because it does not originate from the plane
Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a bo
Uranus's magnetosphere contains charged particles: protons and electrons with small amount of H2+ ions.[90][92] N
Climate
Main article: Climate of Uranus
Uranus's southern hemisphere in approximate natural colour (left) and in shorter wavelengths (right), showing its fain
At ultraviolet and visible wavelengths, Uranus's atmosphere is remarkably bland in comparison to the other gas gian
Banded structure, winds and clouds
Zonal wind speeds on Uranus. Shaded areas show the southern collar and its future northern counterpart. The red c
In 1986 Voyager 2 found that the visible southern hemisphere of Uranus can be subdivided into two regions: a bright

5. The first dark spot observed on Uranus. Image obtained by the HST ACS in 2006.
In the 1990s, the number of the observed bright cloud features grew considerably partly because new high resolution
The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of U
Seasonal variation
Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible (HST ACS image).
For a short period from March to May 2004, a number of large clouds appeared in the Uranian atmosphere, giving it
There are some reasons to believe that physical seasonal changes are happening in Uranus. While the planet is kno
The mechanism of physical changes is still not clear.[102] Near the summer and winter solstices, Uranus's hemisph
Formation
Main article: Formation and evolution of the Solar System
For details of the evolution of Uranus's orbit, see Nice model.
Many argue that the differences between the ice giants and the gas giants extend to their formation.[108][109] The S
Moons
Main article: Moons of Uranus
See also: Timeline of discovery of Solar System planets and their natural satellites
Major moons of Uranus in order of increasing distance (left to right), at their proper relative sizes and albedos (collag
The Uranus System (NACO/VLT image)
Uranus has 27 known natural satellites.[110] The names for these satellites are chosen from characters from the wo
Among the satellites, Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's app
Exploration
Crescent Uranus as imaged by Voyager 2 while departing for Neptune
Main article: Exploration of Uranus
In 1986, NASA's Voyager 2 interplanetary probe encountered Uranus. This flyby remains the only investigation of the
A Uranus orbiter and probe has been recommended by NASA's decadal survey; the proposal envisages launch durin
In culture
In astrology, the planet Uranus () is the ruling planet of Aquarius. Since Uranus is colored cyan and Uranus is associ
The chemical element uranium, discovered in 1789 by the German chemist Martin Heinrich Klaproth, was named aft
See also
Solar System portal
Uranus portal
Book: Solar System
Wikipedia Books are collections of articles that can be downloaded or ordered in print.
Colonization of Uranus
Uranus in astrology
Uranus in fiction
Notes
This article contains special characters. Without proper rendering support, you may see question marks, boxes, or o
^ Orbital elements refer to the barycenter of the Uranus system, and are the instantaneous osculating values at the p
^ Calculated using data from Seidelmann, 2007.[7]
^ Refers to the level of 1 bar atmospheric pressure.

6. ^ Calculation of He, H2 and CH4 molar fractions is based on a 2.3% mixing ratio of methane to hydrogen and the 15
^ Mixing ratio is defined as the number of molecules of a compound per a molecule of hydrogen.
References
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Further reading
Miner, Ellis D. (1998). Uranus: The Planet, Rings and Satellites. New York: John Wiley and Sons. ISBN 047197398X
External links
Find more about Uranus on Wikipedia's sister projects:
Definitions from Wiktionary
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Learning resources from Wikiversity
News stories from Wikinews
Quotations from Wikiquote
Source texts from Wikisource
Textbooks from Wikibooks
Edge On! ESO Press Release
NASA's Uranus fact sheet
Uranus Profile at NASA's Solar System Exploration site
Keck pictures of Uranus show best view from the ground – Press release with some photographs showing rings, sat
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.
Spring Has Sprung on Uranus
Uranus at Jet Propulsion Laboratory's planetary photojournal.
Uranus (Astronomy Cast homepage)
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Categories: Uranus | Gas giant planets | Astronomical objects discovered in 1781

10. th-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus (Ancient Greek: Οὐρανός), the fat
than the larger gas giants Jupiter and Saturn. As such, astronomers sometimes place them in a separate category, the "ice giants". Uranus
oons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane

11. generally mistaken for a star. The earliest recorded sighting was in 1690 when John Flamsteed observed the planet at least six times, catalog
se at 19 New King Street in the town of Bath, Somerset (now the Herschel Museum of Astronomy),[20] but initially reported it (on April 26, 17
s a comet".[23] On March 17, he noted, "I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place".[2
e diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and
s flummoxed reply from him on April 23: "I don't know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to th
ers had already begun to suspect otherwise. Russian astronomer Anders Johan Lexell was the first to compute the orbit of the new object[2
owledged this fact to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that
our planet, which is entirely your own, [and] which we are so much obliged to you for the discovery of."[32] In response to Maskelyne's reques
and Saturn were given to the Planets, as being the names of their principal heroes and divinities. In the present more philosophical era it wou
roposed. Astronomer Jérôme Lalande proposed the planet be named Herschel in honour of its discoverer.[34] Swedish astronomer Erik Pro
with stress on the first syllable as in Latin Ūranus; in contrast to the colloquial /jʊˈreɪnəs/,[39] with stress on the second syllable and a long
r than Roman mythology: the Greek "Οὐρανός" arrived in English by way of the Latin "Ūranus".[1] The adjective of Uranus is "Uranian".[41] It
obtained by the Hubble Space Telescope's NICMOS camera.
Sun is roughly 3 billion km (about 20 AU). The intensity of sunlight on Uranus is about 1/400 that on Earth.[45] Its orbital elements were first c
s, its upper atmosphere experiences very strong winds in the direction of rotation. At some latitudes, such as about two-thirds of the way from
h the plane of the Solar System. This gives it seasonal changes completely unlike those of the other major planets. Other planets can be visu
ranus receive a greater energy input from the Sun than its equatorial regions. Nevertheless, Uranus is hotter at its equator than at its poles. T
g it just within the limit of naked eye visibility at +6.5.[10] Its angular diameter is between 3.4 and 3.7 arcseconds, compared with 16 to 20 ar
ant planets. Its diameter is slightly larger than Neptune's at roughly four times Earth's. A resulting density of 1.27 g/cm3 makes Uranus the se

12. iron-nickel) core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope.[11][58] The core is relatively sm
so satisfy observations. For instance, if substantial amounts of hydrogen and rocky material are mixed in the ice mantle, the total mass of ice
nomical terms, it has a low thermal flux.[18][61] Why Uranus's internal temperature is so low is still not understood. Neptune, which is Uranus
massive impactor, which caused it to expel most of its primordial heat, it was left with a depleted core temperature.[63] Another hypothesis is
f Uranus's gaseous envelope that is accessible to remote sensing is called its atmosphere.[12] Remote sensing capability extends down to r
ng as it does mainly of molecular hydrogen and helium.[12] The helium molar fraction, i.e. the number of helium atoms per molecule of gas, i
yers are also indicated.
a decrease in temperature with altitude.[12] The temperature falls from about 320 K at the base of the nominal troposphere at −300 km to 53
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 M
lly increases with altitude from 53 K in the tropopause to between 800 and 850 K at the base of the thermosphere.[65] The heating of the str
s a uniform temperature around 800 to 850 K.[12][76] The heat sources necessary to sustain such a high value are not understood, since ne
discovered in the Solar System after Saturn's.[80] The rings are composed of extremely dark particles, which vary in size from micrometers
y considered doubtful, as the rings are quite faint, and in the two following centuries none were noted by other observers. Still, Herschel mad
gs. 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
th and north poles.
taken, so its nature remained a mystery. Before 1986, astronomers had expected the magnetic field of Uranus to be in line with the solar wi
ot originate from the planet's geometric center, and because it is tilted at 59° from the axis of rotation.[89][90] In fact the magnetic dipole is sh
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 magne
unt of H2+ ions.[90][92] No heavier ions have been detected. Many of these particles probably derive from the hot atmospheric corona.[92] T
hs (right), showing its faint cloud bands and atmospheric "hood" as seen by Voyager 2
son to the other gas giants, even to Neptune, which it otherwise closely resembles.[18] When Voyager 2 flew by Uranus in 1986, it observed
rn counterpart. The red curve is a symmetrical fit to the data.
into two regions: a bright polar cap and dark equatorial bands (see figure on the right).[17] Their boundary is located at about −45 degrees o

13. cause new high resolution imaging techniques became available.[18] Most were found in the northern hemisphere as it started to become vis
e upper troposphere of Uranus.[18] At the equator winds are retrograde, which means that they blow in the reverse direction to the planetary
sible (HST ACS image).
ian atmosphere, giving it a Neptune-like appearance.[100][104] Observations included record-breaking wind speeds of 229 m/s (824 km/h) a
s. 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 seas
stices, Uranus's hemispheres lie alternately either in full glare of the Sun's rays or facing deep space. The brightening of the sunlit hemispher
ormation.[108][109] The Solar System is believed to have formed from a giant rotating ball of gas and dust known as the presolar nebula. Mu
sizes and albedos (collage of Voyager 2 photographs)
m characters from the works of Shakespeare and Alexander Pope.[58][111] The five main satellites are Miranda, Ariel, Umbriel, Titania and O
ters, while Umbriel's appears oldest.[17][81] Miranda possesses fault canyons 20 kilometers deep, terraced layers, and a chaotic variation in
e only investigation of the planet carried out from a short distance, and no other visits are currently planned. Launched in 1977, Voyager 2 m
sal envisages launch during 2020-2023 and a 13-year cruise to Uranus.
yan and Uranus is associated with electricity, the color electric blue, a color close to cyan, is associated with the sign Aquarius.[118] (See Ura
Klaproth, was named after the newly discovered planet Uranus.[119] Uranus, the Magician is a movement in Gustav Holst's The Planets, w
estion marks, boxes, or other symbols.
osculating values at the precise J2000 epoch. Barycenter quantities are given because, in contrast to the planetary center, they do not exper

14. e to hydrogen and the 15/85 He/H2 proportions measured at the tropopause.
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18. Greek: Οὐρανός), the father of Cronus (Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the naked eye like the five classical
, the "ice giants". Uranus's atmosphere, while similar to Jupiter and Saturn's in its primary composition of hydrogen and helium, contains mo
ays, nearly into the plane of its revolution about the Sun. As such, its north and south poles lie where most other planets have their equators.

19. at least six times, cataloging it as 34 Tauri. The French astronomer Pierre Lemonnier observed Uranus at least twelve times between 1750
eported it (on April 26, 1781) as a "comet".[21] Herschel "engaged in a series of observations on the parallax of the fixed stars",[22] using a te
has changed its place".[24] When he presented his discovery to the Royal Society, he continued to assert that he had found a comet while a
ut 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 suppos
orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it".[26]
orbit of the new object[27] and its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Joh
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
se to Maskelyne's request, Herschel decided to name the object Georgium Sidus (George's Star), or the "Georgian Planet" in honour of his
e philosophical era it would hardly be allowable to have recourse to the same method and call it Juno, Pallas, Apollo or Minerva, for a name t
dish astronomer Erik Prosperin proposed the name Neptune which was supported by other astronomers who liked the idea to commemorate
cond syllable and a long a, though both are considered acceptable. Because, in the English-speaking world, ū·rā′·nəs sounds like "your anus
Uranus is "Uranian".[41] Its astronomical symbol is . It is a hybrid of the symbols for Mars and the Sun because Uranus was the Sky in Greek
bital elements were first calculated in 1783 by Pierre-Simon Laplace.[46] With time, discrepancies began to appear between the predicted an
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 lit
Other planets can be visualized to rotate like tilted spinning tops on the plane of the Solar System, while Uranus rotates more like a tilted roll
quator than at its poles. The underlying mechanism which causes this is unknown. The reason for Uranus's unusual axial tilt is also not know
ompared with 16 to 20 arcseconds for Saturn and 32 to 45 arcseconds for Jupiter.[10] At opposition, Uranus is visible to the naked eye in da
m3 makes Uranus the second least dense planet, after Saturn.[7][9] This value indicates that it is made primarily of various ices, such as wa

20. The core is relatively small, with a mass of only 0.55 Earth masses and a radius less than 20% of Uranus's; the mantle comprises the bulk o
ntle, the total mass of ices in the interior will be lower, and, correspondingly, the total mass of rocks and hydrogen will be higher. Presently a
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.[18
3] Another hypothesis is that some form of barrier exists in Uranus's upper layers which prevents the core's heat from reaching the surface.[
pability extends down to roughly 300 km below the 1 bar (100 kPa) level, with a corresponding pressure around 100 bar (10 MPa) and tempe
ms per molecule of gas, is 0.15 ± 0.03[14] in the upper troposphere, which corresponds to a mass fraction 0.26 ± 0.05.[12][62] This value is
osphere at −300 km to 53 K at 50 km.[64][67] The temperatures in the coldest upper region of the troposphere (the tropopause) actually vary
e of 20 to 40 bar (2 to 4 MPa), ammonia or hydrogen sulfide clouds at between 3 and 10 bar (0.3 to 1 MPa) and finally directly detected thin
65] The heating of the stratosphere is caused by absorption of solar UV and IR radiation by methane and other hydrocarbons,[75] which form
not understood, since neither solar far UV and extreme UV radiation nor auroral activity can provide the necessary energy. The weak cooling
n size from micrometers to a fraction of a meter.[17] Thirteen distinct rings are presently known, the brightest being the ε ring. All except two
rvers. Still, Herschel made an accurate description of the epsilon ring's size, its angle relative to the Earth, its red color, and its apparent cha
o far from the planet that they are called the "outer" ring system. Hubble also spotted two small satellites, one of which, Mab, shares its orbit
be in line with the solar wind, since it would then align with the planet's poles that lie in the ecliptic.[89]
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.
, a fully developed magnetotail and radiation belts.[89][90][92] Overall, the structure of Uranus's magnetosphere is different from Jupiter's an
tmospheric corona.[92] The ion and electron energies can be as high as 4 and 1.2 megaelectronvolts, respectively.[92] The density of low en
anus in 1986, it observed a total of ten cloud features across the entire planet.[17][95] One proposed explanation for this dearth of features is
d at about −45 degrees of latitude. A narrow band straddling the latitudinal range from −45 to −50 degrees is the brightest large feature on th

21. s it started to become visible.[18] An early explanation—that bright clouds are easier to identify in the dark part of the planet, whereas in the
direction to the planetary rotation. Their speeds are from −100 to −50 m/s.[18][96] Wind speeds increase with the distance from the equator
s of 229 m/s (824 km/h) and a persistent thunderstorm referred to as "Fourth of July fireworks".[95] On August 23, 2006, researchers at the S
ith the model of the seasonal change outlined above.[102] During its previous northern solstice in 1944, Uranus displayed elevated levels of
ng of the sunlit hemisphere is thought to result from the local thickening of the methane clouds and haze layers located in the troposphere.[97
s the presolar nebula. Much of the nebula's gas, primarily hydrogen and helium, formed the Sun, while the dust grains collected together to fo
iel, Umbriel, Titania and Oberon.[58] The Uranian satellite system is the least massive among the gas giants; indeed, the combined mass of
and a chaotic variation in surface ages and features.[17] Miranda's past geologic activity is believed to have been driven by tidal heating at a
hed in 1977, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers of the planet's cloudtops
n Aquarius.[118] (See Uranus in astrology)
av Holst's The Planets, written between 1914 and 1916. Operation Uranus was the successful military operation in World War II by the Sovie
center, they do not experience appreciable changes on a day-to-day basis from the motion of the moons.

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26. eye like the five classical planets, it was never recognized as a planet by ancient observers because of its dimness and slow orbit.[16] Sir Wi
and helium, contains more "ices" such as water, ammonia and methane, along with traces of hydrocarbons.[12] It is the coldest planetary atm
nets have their equators.[17] Seen from Earth, Uranus's rings can sometimes appear to circle the planet like an archery target and its moons

27. elve times between 1750 and 1769,[19] including on four consecutive nights.
fixed stars",[22] using a telescope of his own design.
ad found a comet while also implicitly comparing it to a planet:[25]
ught 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 sa
et. Berlin astronomer Johann Elert Bode described Herschel's discovery as "a moving star that can be deemed a hitherto unknown planet-lik
Planet of our Solar System."[30] In recognition of his achievement, King George III gave Herschel an annual stipend of £200 on the condition
Planet" in honour of his new patron, King George III.[33] He explained this decision in a letter to Joseph Banks:[30]
o or Minerva, for a name to our new heavenly body. The first consideration of any particular event, or remarkable incident, seems to be its ch
the idea to commemorate the victories of the British Royal Naval fleet in the course of the American Revolutionary War by calling the new pla
əs sounds like "your anus", the former pronunciation also saves embarrassment: as Dr. Pamela Gay, an astronomer at Southern Illinois Univ
nus was the Sky in Greek mythology, which was thought to be dominated by the combined powers of the Sun and Mars.[42] Its astrological s
between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitati
king a full rotation in as little as 14 hours.[48]
ates more like a tilted rolling ball. Near the time of Uranian solstices, one pole faces the Sun continuously while the other pole faces away. O
al axial tilt is also not known with certainty, but the usual speculation is that during the formation of the Solar System, an Earth sized protoplan
le to the naked eye in dark skies, and becomes an easy target even in urban conditions with binoculars.[8] In larger amateur telescopes with
various ices, such as water, ammonia, and methane.[11] The total mass of ice in Uranus's interior is not precisely known, as different figure

28. antle comprises the bulk of the planet, with around 13.4 Earth masses, while the upper atmosphere is relatively insubstantial, weighing about
will be higher. Presently available data does not allow science to determine which model is correct.[57] The fluid interior structure of Uranus m
eceives from the Sun.[18] Uranus, by contrast, radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (
om reaching the surface.[11] For example, convection may take place in a set of compositionally different layers, which may inhibit the upwar
bar (10 MPa) and temperature of 320 K.[64] The tenuous corona of the atmosphere extends remarkably over two planetary radii from the no
.05.[12][62] This value is very close to the protosolar helium mass fraction of 0.275 ± 0.01,[66] indicating that helium has not settled in the ce
tropopause) actually vary in the range between 49 and 57 K depending on planetary latitude.[12][61] The tropopause region is responsible fo
ally directly detected thin methane clouds at 1 to 2 bar (0.1 to 0.2 MPa).[12][13][64][74] The troposphere is a very dynamic part of the atmosp
rocarbons,[75] which form in this part of the atmosphere as a result of methane photolysis.[70] Heat is also conducted from the hot thermosp
energy. The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0.1 mBar pressure level may contribute too.[6
the ε ring. All except two rings of Uranus are extremely narrow—they are usually a few kilometres wide. The rings are probably quite young;
olor, and its apparent changes as Uranus traveled around the Sun.[82][83] The ring system was definitively discovered on March 10, 1977 by
ich, Mab, shares its orbit with the outermost newly discovered ring. The new rings bring the total number of Uranian rings to 13.[85] In April 2
d of the planetary radius.[89] This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the
different from Jupiter's and more similar to Saturn's.[89][90] Uranus's magnetotail trails behind the planet into space for millions of kilometers
[92] The density of low energy (below 1 kiloelectronvolt) ions in the inner magnetosphere is about 2 cm−3.[94] The particle population is stro
r this dearth of features is that Uranus's internal heat appears markedly lower than that of the other giant planets. The lowest temperature re
ghtest large feature on the visible surface of the planet.[17][96] It is called a southern "collar". The cap and collar are thought to be a dense r

29. he planet, whereas in the southern hemisphere the bright collar masks them—was shown to be incorrect: the actual number of features has
distance from the equator, reaching zero values near ±20° latitude, where the troposphere's temperature minimum is located.[18][61] Closer
2006, researchers at the Space Science Institute (Boulder, CO) and the University of Wisconsin observed a dark spot on Uranus's surface, g
played elevated levels of brightness, which suggests that the north pole was not always so dim.[105] This information implies that the visible
ted in the troposphere.[97] The bright collar at −45° latitude is also connected with methane clouds.[97] Other changes in the southern polar
ns collected together to form the first protoplanets. As the planets grew, some of them eventually accreted enough matter for their gravity to h
d, the combined mass of the five major satellites would be less than half that of Triton alone.[9] The largest of the satellites, Titania, has a ra
riven 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 resonan
of the planet's cloudtops, before continuing its journey to Neptune. Voyager 2 studied the structure and chemical composition of Uranus's at
World War II by the Soviet army to take back Stalingrad and marked the turning point in the land war against the Wehrmacht.

31. gust 5, 2007.

34. and slow orbit.[16] Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the Solar System f
s the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (–224 °C). It has a complex, layered cloud stru
hery target and its moons revolve around it like the hands of a clock, though in 2007 and 2008 the rings appeared edge-on. In 1986, images

35. re not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-de
therto unknown planet-like object circulating beyond the orbit of Saturn".[28] Bode concluded that its near-circular orbit was more like a plane
of £200 on the condition that he move to Windsor so that the Royal Family could have a chance to look through his telescopes.[31]
cident, 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 sat
War by calling the new planet even Neptune George III or Neptune Great Britain.[27] Bode opted for Uranus, the Latinized version of the Gre
r at Southern Illinois University Edwardsville, noted on her podcast, to avoid "being made fun of by any small schoolchildren ... when in doub
Mars.[42] Its astrological symbol is , suggested by Lalande in 1784. In a letter to Herschel, Lalande described it as "un globe surmonté par la p
ght be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. O
other pole faces away. Only a narrow strip around the equator experiences a rapid day-night cycle, but with the Sun very low over the horizon
, an Earth sized protoplanet collided with Uranus, causing the skewed orientation.[52] Uranus's south pole was pointed almost directly at the
amateur telescopes with an objective diameter of between 15 and 23 cm, the planet appears as a pale cyan disk with distinct limb darkenin
known, as different figures emerge depending on the model chosen; it must be between 9.3 and 13.5 Earth masses.[11][57] Hydrogen and h

36. bstantial, weighing about 0.5 Earth masses and extending for the last 20% of Uranus's radius.[11][58] Uranus's core density is around 9 g/cm
rior structure of Uranus means that it has no solid surface. The gaseous atmosphere gradually transitions into the internal liquid layers.[11] F
ranus in the far infrared (i.e. heat) part of the spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere.[12][62] In fact, Uran
ich may inhibit the upward heat transport.[12][62]
planetary radii from the nominal surface at 1 bar pressure.[65] The Uranian atmosphere can be divided into three layers: the troposphere, be
m has not settled in the center of the planet as it has in the gas giants.[12] The third most abundant constituent of the Uranian atmosphere is
e region is responsible for the vast majority of the planet’s thermal far infrared emissions, thus determining its effective temperature of 59.1 ±
ynamic part of the atmosphere, exhibiting strong winds, bright clouds and seasonal changes, which will be discussed below.[18]
ed from the hot thermosphere.[75] The hydrocarbons occupy a relatively narrow layer at altitudes of between 100 and 300 km corresponding
evel may contribute too.[65][76] In addition to molecular hydrogen, the thermosphere-corona contains many free hydrogen atoms. Their smal
are probably quite young; the dynamics considerations indicate that they did not form with Uranus. The matter in the rings may once have be
ed on March 10, 1977 by James L. Elliot, Edward W. Dunham, and Douglas J. Mink using the Kuiper Airborne Observatory. The discovery w
rings to 13.[85] In April 2006, images of the new rings with the Keck Observatory yielded the colours of the outer rings: the outermost is blue
gnetic 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 ca
for millions of kilometers and is twisted by the planet's sideways rotation into a long corkscrew.[89][93]
particle population is strongly affected by the Uranian moons that sweep through the magnetosphere leaving noticeable gaps.[92] The partic
he lowest temperature recorded in Uranus's tropopause is 49 K, making Uranus the coldest planet in the Solar System, colder than Neptune
e thought to be a dense region of methane clouds located within the pressure range of 1.3 to 2 bar (see above).[97] Besides the large-scale

37. number of features has indeed increased considerably.[99][100] Nevertheless there are differences between the clouds of each hemisphere
s located.[18][61] Closer to the poles, the winds shift to a prograde direction, flowing with the planet's rotation. Windspeeds continue to increa
ot on Uranus's surface, giving astronomers more insight into the planet's atmospheric activity.[101] Why this sudden upsurge in activity shou
on implies that the visible pole brightens some time before the solstice and darkens after the equinox.[102] Detailed analysis of the visible an
ges in the southern polar region can be explained by changes in the lower cloud layers.[97] The variation of the microwave emission from the
matter for their gravity to hold onto the nebula's leftover gas.[108][109] The more gas they held onto, the larger they became; the larger they
atellites, 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 S
resent 3:1 orbital resonance with Umbriel.[113] Extensional processes associated with upwelling diapirs are the likely origin of the moon's 'ra
omposition of Uranus's atmosphere,[67] including the planet's unique weather, caused by its axial tilt of 97.77°. It made the first detailed inves

42. ies of the Solar System for the first time in modern history. Uranus was also the first planet discovered with a telescope.
mplex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clo
edge-on. In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms as

43. , appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand ob
rbit was more like a planet than a comet.[29]
telescopes.[31]
ed? It would be a very satisfactory answer to say, 'In the reign of King George the Third' .ˈ‖
tinized version of the Greek god of the sky, Ouranos. Bode argued that just as Saturn was the father of Jupiter, the new planet should be nam
lchildren ... when in doubt, don't emphasise anything and just say ūr′·ə·nəs. And then run, quickly."[40]
n globe surmonté par la première lettre de votre nom" ("a globe surmounted by the first letter of your surname").[34] In the Chinese, Japanes
rch into Uranus's orbit. On September 23, 1846, Johann Gottfried Galle located a new planet, later named Neptune, at nearly the position pr
very low over the horizon as in the Earth's polar regions. At the other side of Uranus's orbit the orientation of the poles towards the Sun is re
ted almost directly at the Sun at the time of Voyager 2's flyby in 1986. The labeling of this pole as "south" uses the definition currently endors
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
.[11][57] Hydrogen and helium constitute only a small part of the total, with between 0.5 and 1.5 Earth masses.[11] The remainder of the non

44. e density is around 9 g/cm3, with a pressure in the center of 8 million bars (800 GPa) and a temperature of about 5000 K.[57][58] The ice ma
nternal liquid layers.[11] For the sake of convenience, a revolving oblate spheroid set at the point at which atmospheric pressure equals 1 ba
here.[12][62] In fact, Uranus's 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.[
yers: the troposphere, between altitudes of −300 and 50 km and pressures from 100 to 0.1 bar; (10 MPa to 10 kPa), the stratosphere, spann
e Uranian atmosphere is methane (CH4).[12] Methane possesses prominent absorption bands in the visible and near-infrared (IR) making U
ive temperature of 59.1 ± 0.3 K.[61][62]
d below.[18]
nd 300 km corresponding to a pressure range of 10 to 0.1 mbar (1000 to 10 kPa) and temperatures of between 75 and 170 K.[68][71] The m
drogen atoms. Their small mass together with the high temperatures explain why the corona extends as far as 50 000 km or two Uranian rad
rings may once have been part of a moon (or moons) that was shattered by high-speed impacts. From numerous pieces of debris that form
ervatory. The discovery was serendipitous; they planned to use the occultation of the star SAO 158687 by Uranus to study the planet's atmos
ngs: the outermost is blue and the other red.[86][87] One hypothesis concerning the outer ring's blue colour is that it is composed of minute p
northern hemisphere it can be as high as 1.1 gauss (110 µT).[89] The average field at the surface is 0.23 gauss (23 µT).[89] In comparison, t
able gaps.[92] The particle flux is high enough to cause darkening or space weathering of the moon’s surfaces on an astronomically rapid tim
em, colder than Neptune.[12][62]
Besides the large-scale banded structure, Voyager 2 observed ten small bright clouds, most lying several degrees to the north from the coll

45. ouds of each hemisphere. The northern clouds are smaller, sharper and brighter.[100] They appear to lie at a higher altitude.[100] The lifetim
speeds continue to increase reaching maxima at ±60° latitude before falling to zero at the poles.[18] Windspeeds at −40° latitude range from
n upsurge in activity should be occurring is not fully known, but it appears that Uranus's extreme axial tilt results in extreme seasonal variatio
analysis of the visible and microwave data revealed that the periodical changes of brightness are not completely symmetrical around the sol
rowave emission from the planet is probably caused by a changes in the deep tropospheric circulation, because thick polar clouds and haze
became; the larger they became, the more gas they held onto until a critical point was reached, and their size began to increase exponentia
second largest moon of Saturn, making Titania the eighth largest moon in the Solar System. The moons have relatively low albedos; ranging
y origin of the moon's 'racetrack'-like coronae.[114][115] Similarly, Ariel is believed to have once been held in a 4:1 resonance with Titania.[1
ade the first detailed investigations of its five largest moons, and discovered 10 new moons. It examined all nine of the system's known rings

50. he uppermost layer of clouds.[12] In contrast, the interior of Uranus is mainly composed of ices and rock.[11]
cloud bands or storms associated with the other giants.[17] Terrestrial observers have seen signs of seasonal change and increased weathe

51. h from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be
new planet should be named after the father of Saturn.[31][35][36] In 1789, Bode's Royal Academy colleague Martin Klaproth named his new
] In the Chinese, Japanese, Korean, and Vietnamese languages, the planet's name is literally translated as the sky king star ( 天王星).[43][44
e, at nearly the position predicted by Le Verrier.[47]
oles towards the Sun is reversed. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.[49] Near the time
definition currently endorsed by the International Astronomical Union, namely that the north pole of a planet or satellite shall be the pole which
atellites, such as Titania and Oberon, may be visible.[56]
The remainder of the non-ice mass (0.5 to 3.7 Earth masses) is accounted for by rocky material.[11]

52. 000 K.[57][58] The ice mantle is not in fact composed of ice in the conventional sense, but of a hot and dense fluid consisting of water, amm
eric pressure equals 1 bar (100 kPa) is conditionally designated as a "surface". It has equatorial and polar radii of 25 559 ± 4 and 24 973 ± 20
th of about 0.075 W/m2.[62] The lowest temperature recorded in Uranus's tropopause is 49 K (–224 °C), making Uranus the coldest planet i
, the stratosphere, spanning altitudes between 50 and 4000 km and pressures of between 0.1 and 10–10 bar (10 kPa to 10 µPa), and the th
ar-infrared (IR) making Uranus aquamarine or cyan in color.[12] Methane molecules account for 2.3% of the atmosphere by molar fraction be
and 170 K.[68][71] The most abundant hydrocarbons are methane, acetylene and ethane with mixing ratios of around 10−7 relative to hydrog
00 km or two Uranian radii from the planet.[65][76] This extended corona is a unique feature of Uranus.[76] Its effects include a drag on sma
pieces of debris that formed as result of those impacts only few particles survived in a limited number of stable zones corresponding to prese
o study the planet's atmosphere. When their observations were analyzed, they found that the star had disappeared briefly from view five time
is composed of minute particles of water ice from the surface of Mab that are small enough to scatter blue light.[86][88] In contrast, the plan
µT).[89] In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its g
an astronomically rapid timescale of 100,000 years.[92] This may be the cause of the uniformly dark colouration of the moons and rings.[81] U
to the north from the collar.[17] In all other respects Uranus looked like a dynamically dead planet in 1986. Unfortunately Voyager 2 arrived d

53. er altitude.[100] The lifetime of clouds spans several orders of magnitude. Some small clouds live for hours, while at least one southern cloud
t −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 a
xtreme seasonal variations in its weather.[51][102] Determining the nature of this seasonal variation is difficult because good data on Uranus
mmetrical around the solstices, which also indicates a change in the meridional albedo patterns.[102] Finally in the 1990s, as Uranus moved
ck polar clouds and haze may inhibit convection.[107] Now that the spring and autumn equinoxes are arriving on Uranus, the dynamics are c
n to increase exponentially. The ice giants, with only a few Earth masses of nebular gas, never reached that critical point.[108][109][110] Rec
vely low albedos; ranging from 0.20 for Umbriel to 0.35 for Ariel (in green light).[17] The moons are ice-rock conglomerates composed of rou
resonance with Titania.[116]
he system's known rings, discovering two new ones.[17][81][117] It also studied the magnetic field, its irregular structure, its tilt and its uniqu

58. ge and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per

59. unded, this proving to be the Comet we have lately observed.ˈ‖
n Klaproth named his newly discovered element "uranium" in support of Bode's choice.[37] Ultimately, Bode's suggestion became the most w
king star ( 天王星).[43][44]
rkness.[49] 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
te shall be the pole which points above the invariable plane of the Solar System, regardless of the direction the planet is spinning.[53][54] A

60. consisting of water, ammonia and other volatiles.[11][58] This fluid, which has a high electrical conductivity, is sometimes called a water–amm
5 559 ± 4 and 24 973 ± 20 km, respectively.[7] This surface will be used throughout this article as a zero point for altitudes.
ranus the coldest planet in the Solar System.[12][62]
Pa to 10 µPa), and the thermosphere/corona extending from 4,000 km to as high as 50,000 km from the surface.[12] There is no mesosphe
phere 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 ca
nd 10−7 relative to hydrogen. The mixing ratio of carbon monoxide is similar at these altitudes.[68][71][73] Heavier hydrocarbons and carbon
ts include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings.[65] The Uranian thermosphere,
s corresponding to present rings.[80][81]
briefly from view five times both before and after it disappeared behind the planet. They concluded that there must be a ring system around t
6][88] In contrast, the planet's inner rings appear grey.[86]
roughly parallel with its geographical equator.[90] The dipole moment of Uranus is 50 times that of Earth.[89][90] Neptune has a similarly dis
he moons and rings.[81] Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles.[76] Unlike
nately Voyager 2 arrived during the height of the planet's southern summer and could not observe the northern hemisphere. At the beginning

61. least one southern cloud may have persisted since Voyager flyby.[18][95] Recent observation also discovered that cloud features on Uranus
t and the southern pole are impossible to measure.[18] In contrast, in the northern hemisphere maximum speeds as high as 240 m/s are ob
use good data on Uranus's atmosphere have existed for less than 84 years, or one full Uranian year. A number of discoveries have been ma
1990s, as Uranus moved away from its solstice, Hubble and ground based telescopes revealed that the south polar cap darkened noticeably
anus, the dynamics are changing and convection can occur again.[95][107]
point.[108][109][110] Recent simulations of planetary migration have suggested that both ice giants formed closer to the Sun than their pres
merates composed of roughly fifty percent ice and fifty percent rock. The ice may include ammonia and carbon dioxide.[81][112]
cture, its tilt and its unique corkscrew magnetotail caused by Uranus's sideways orientation.[89]

66. can reach 250 meters per second (900 km/h, 560 mph).[18]

67. estion became the most widely used, and became universal in 1850 when HM Nautical Almanac Office, the final holdout, switched from using
similar to those seen on most of the other planets. Uranus reached its most recent equinox on December 7, 20
net is spinning.[53][54] A different convention is sometimes used, in which a body's north and south poles a

68. times called a water–ammonia ocean.[59] The bulk compositions of Uranus and Neptune are very different from those of J
2] There is no mesosphere.
out 20 to 30 times the carbon abundance found in the Sun.[12][13][67] The mixing ratio[e] is much lower in the upper atmosphere o
hydrocarbons and carbon dioxide have mixing ratios three orders of magnitude lower.[71] The abundance ratio of water is around 7×10−9.[72
e Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus.[67] Observations show
be a ring system around the planet.[84] Later they detected four additional rings.[84] The rings were directly imaged when Voyage
eptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice gia
magnetic poles.[76] Unlike Jupiter's, Uranus's aurorae seem to be insignificant for the energy balance of the planetary thermosphere.[79]
isphere. At the beginning of the 21st century, when the northern polar region came into view, the Hubble Space Telescop

69. cloud features on Uranus have a lot in common with those on Neptune.[18] For example, the dark spots common on Neptune had never be
s high as 240 m/s are observed near +50 degrees of latitude.[18][96][103]
discoveries have been made. Photometry over the course of half a Uranian year (beginning in the 1950s) has shown regular variatio
cap darkened noticeably (except the southern collar, which remained bright),[97] while the northern hemisphere demonstrated in
o the Sun than their present positions, and moved outwards after formation, a hypothesis which is detailed in the Nice mo
de.[81][112]

75. dout, switched from using Georgium Sid

76. er atmosphere o
ater is around 7×10−9.[72] Etha
.[67] Observations show
when Voyage
y thermosphere.[79]

77. on Neptune had never been
n regular variatio
emonstrated in