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Uranus

Uranus Uranus presented a featureless disk to Voyager 2 in 1986. Its appearance reflects the presence of a high-altitude hydrocarbon photochemical haze overlying clouds of methane, which in turn overlie clouds of hydrogen sulfide and/or ammonia (below these are additional unseen cloud decks of different compositions). The blue-green coloration results from the absorption bands of methane. Discovery Discovered by William Herschel Discovery date March 13, 1781 Designations Pronunciation i/'j??r?n?s/ or i/j?'re?n?s/ Adjective Uranian Orbital characteristics 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 Synodic period 369.66 days Average orbital speed 6.81 km/s Mean anomaly 142.955 717° Inclination 0.772 556° to Ecliptic 6.48° to Sun's equator 1.02° to Invariable plane 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 Polar radius 24,973 ± 20 km 3.929 Earths Flattening 0.022 9 ± 0.000 8 Circumference 159,354.1 km Surface area 8.115 6×109 km2 15.91 Earths Volume 6.833×1013 km3 63.086 Earths Mass (8.6810 ± 0.0013)×1025 kg 14.536 Earths GM=5 793 939 ± 13 km3/s2 Mean density 1.27 g/cm3 Equatorial surface gravity 8.69 m/s2 0.886 g Escape velocity 21.3 km/s Sidereal rotation period 0.718 33 day (Retrograde) 17 h 14 min 24 s Equatorial rotation velocity 2.59 km/s 9,320 km/h Axial tilt 97.77° North pole right ascension 17 h 9 min 15 s 257.311° North pole declination -15.175° Albedo 0.300 (Bond) 0.51 (geom.) Surface temp. min mean max 1 bar level 76 K 0.1 bar (tropopause) 49 K 53 K 57 K Apparent magnitude 5.9 to 5.32 Angular diameter 3.3"–4.1" Atmosphere Scale height 27.7 km Composition (Below 1.3 bar) 83 ± 3% hydrogen (H2) 15 ± 3% helium (He) 2.3% methane (CH4) 0.009% (0.007–0.015%) hydrogen deuteride (HD) Ices:* ammonia (NH3)* water (H2O)* ammonium hydrosulfide (NH4SH)* methane ice (?) (CH4•5.75H2O) This article contains special characters. Without proper rendering support, you may see question marks, boxes, or other symbols. Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giants Jupiter and Saturn. For this reason, astronomers sometimes place them in a separate category called "ice giants". Uranus's atmosphere, although similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia, and methane, along with traces of hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (-224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds. In contrast, the interior of Uranus is mainly composed of ices and rock.Like the other gas giants, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun. Its north and south poles therefore lie where most other planets have their equators. In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants. Terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second (900 km/h, 560 mph). Cite error: There are tags on this page, but the references will not show without a {{Reflist}} template or a tag (see the help page). Cite error: There are tags on this page, but the references will not show without a {{Reflist|group=lower-alpha}} template or a tag (see the help page).
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