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Uranus Astronomical symbol of Uranus
Uranus, as seen by Voyager 2
Discovered by William Herschel
Discovery date March 13, 1781
Adjectives 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
2 876 679 082 km
19.229 411 95 AU
Eccentricity 0.044 405 586
30 799.095 days
84.323 326 yr
369.66 days
6.81 km/s
142.955 717°
Inclination 0.772 556°
6.48° to Sun's equator
73.989 821°
96.541 318°
Known satellites 27
Physical characteristics
Mean radius
25,362±7 km
Flattening 0.022 9 ± 0.000 8
8.115 6×109 km²
15.91 Earths
Volume 6.833×1013 km³
63.086 Earths

(8.6810 ± 0.0013)×1025 kg
14.536 Earths

GM=5 793 939 ± 13 km³/s²
Mean density
1.27 g/cm³
8.69 m/s²
0.886 g
21.3 km/s
Equatorial rotation velocity
2.59 km/s
9,320 km/h
North pole right ascension
17 h 9 min 15 s
North pole declination

0.300 (bond)

0.51 (geom.)
Surface temp. min mean max
bar level 76 K
0.1 bar
49 K 53 K 57 K
5.9 to 5.32
Angular diameter
27.7 km
Composition by volume

(Below 1.3 bar)
83 ± 3% hydrogen (H2)
15 ± 3% helium
2.3% methane
0.009% hydrogen deuteride (HD)

ammonium hydrosulfide (NH4SH)
methane (CH4)

Uranus is the seventh planet from the Sun in the Solar System. It is a gas giant. It is the third largest planet in the solar system. The planet is made of ice, gases and liquid metal. Its atmosphere contains hydrogen, helium and methane. The temperature on Uranus is −197 degrees C (79 K) near the top of its atmosphere, but its small solid core (about 55% the mass of Earth) is probably about 5,000K. The planet is tilted on its axis so much that it is sideways.

Uranus completes its orbit around the Sun in 84 earth years. It completes its turn around itself in 17 hours and 14 minutes. This means there are about 43,000 days in 1 uranian year.

The distance between Uranus and Neptune is 1.6 billion km. Uranus was discovered in 1781. Uranus has 13 known rings which are hard to see from earth.

This planet can be seen with the naked eye under perfect conditions. Some evidence suggests that this planet was catalogued as a star (34 Tauri) before its confirmed discovery.

Uranus is named after the Greek god Uranus, who was a god of sky.


Uranus has 27 known moons. The names for these moons are chosen from characters from the works of Shakespeare and Alexander Pope.

The five biggest moons are Miranda, Ariel, Umbriel, Titania and Oberon. Many moons have yet to be discovered. They remain a mystery.


In 1986, NASA's Voyager 2 visited Uranus. The visit is the only attempt to investigate the planet from a short distance.


Uranus is covered in blue clouds. The clouds, made of methane, are difficult to see as they are low in the atmosphere. There are also violent storms on the surface with winds that blow at 160 miles per hour. Scientists are studying the clouds to try and understand the storms on the planet.


Uranian rings scheme
The scheme of Uranus's ring-moon system. Solid lines denote rings; dashed lines denote orbits of moons

The planet Uranus has a system made of 13 rings between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune. The rings of Uranus were discovered in 1977. More than 200 years ago, William Herschel also reported observing rings, but modern astronomers do not believe that he saw them, because they are very dark and faint. Two additional rings were discovered in 1986 in images taken by the Voyager 2, and two outer rings were found in 2003–2005 by the Hubble Space Telescope. The rings are probably mainly composed of water.


The rings of Uranus are thought to be relatively young, not more than 600 million years old. The Uranian ring system probably began from the collisional fragmentation of moons that once existed around the planet. After colliding, the moons probably broke up into many particles, which survived as narrow, optically dense rings only in zones of maximum stability.

General properties

Uranian rings PIA01977
Uranus's inner rings. The bright outer ring is the epsilon ring; eight other rings are visible

The ring system of Uranus has thirteen distinct rings. In order of increasing distance from the planet they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. They can be divided into three groups: nine narrow main rings (6, 5, 4, α, β, η, γ, δ, ε), two dusty rings (1986U2R/ζ, λ) and two outer rings (μ, ν). The rings of Uranus consist mainly of macroscopic particles and little dust, although dust is known to be present in 1986U2R/ζ, η, δ, λ, ν and μ rings.

In addition to these well-known rings, there may be numerous optically thin dust bands and faint rings between them. These faint rings and dust bands may exist only temporarily. Some of them became visible during a series of ring plane-crossing events in 2007. A number of dust bands between the rings were observed in forward-scattering geometry by Voyager 2. All rings of Uranus show azimuthal brightness variations.

The rings are made of an extremely dark material. The rings are slightly red in the ultraviolet and visible parts of the spectrum and grey in near-infrared. They show no identifiable spectral features. The chemical composition of the ring particles is not known. However, they cannot be made of pure water ice like the rings of Saturn because they are too dark, darker than the inner moons of Uranus. This shows that they are probably composed of a mixture of the ice and a dark material. The nature of this material is not clear, but it may be organic compounds considerably darkened by the charged particle irradiation from the Uranian magnetosphere. The rings' particles may consist of a heavily processed material which was initially similar to that of the inner moons.

Uranus Orbit
Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU)
A 1998 false-colour near-infrared image of Uranus showing cloud bands, rings, and moons obtained by the Hubble Space Telescope's NICMOS camera

As a whole, the ring system of Uranus is unlike either the faint dusty rings of Jupiter or the broad and complex rings of Saturn, some of which are composed of very bright material—water ice. However, there are similarities with some parts of the latter ring system; the Saturnian F ring and the ε ring are both narrow, relatively dark and are shepherded by a pair of moons. The newly discovered outer rings of Uranus are similar to the outer G and E rings of Saturn. Narrow ringlets existing in the broad Saturnian rings also resemble the narrow rings of Uranus. In addition, dust bands observed between the main rings of Uranus may be similar to the rings of Jupiter. In contrast, the Neptunian ring system is quite similar to that of Uranus, although it is less complex, darker and contains more dust. The Neptunian rings are also positioned further from the planet.

Orbit and rotation

Uranus revolves around the Sun once every 84 Earth years. Its average distance from the Sun is roughly 3 billion km (about 20 AU). The intensity of sunlight on Uranus is about 1/400 that on Earth. Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace. With time, discrepancies began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first proposed that the differences might be due to the gravitational tug of an unseen planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On September 23, 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, clockwise (retrograde). As on all giant planets, its upper atmosphere experiences very strong winds in the direction of rotation. At some latitudes, such as about two-thirds of the way from the equator to the south pole, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.

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