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Once considered one of the blander-looking planets, Uranus (pronounced YOOR un nus) has been revealed as a dynamic world with some of the brightest clouds in the outer solar system and 11 rings. Uranus gets its blue-green color from methane gas above the deeper cloud layers (methane absorbs red light and reflects blue light).

Uranus was discovered in 1781 by astronomer William Herschel, who at first believed it to be a comet. This seventh planet from the Sun is so distant that it takes 84 years to complete an orbit.

Uranus is classified as a "gas giant" planet because it has no solid surface. The atmosphere of Uranus is hydrogen and helium, with a small amount of methane and traces of water and ammonia. The bulk (80 percent or more) of the mass of Uranus is contained in an extended liquid core consisting primarily of "icy" materials (water, methane, and ammonia), with higher-density material at depth.

In 1986, Voyager 2 observed faint cloud markings in the southern latitudes blowing westward between 100 and 600 km/hr. In 1998, the Hubble Space Telescope observed as many as 20 bright clouds at various altitudes in Uranus' atmosphere. The bright clouds are probably made of crystals of methane, which condense as warm bubbles of gas well up from deep in the atmosphere of Uranus.

Uranus currently moves around the Sun with its rotation axis nearly horizontal with respect to the ecliptic plane. This unusual orientation may be the result of a collision with a planet-sized body early in the planet's history, which apparently changed Uranus' rotation radically.

Uranus' magnetic field is unusual in that the magnetic axis is tilted 60 degrees from the planet's axis of rotation and is offset from the center of the planet by one-third of the planet's radius.

Uranus is so far from the Sun that, even though tipped on its side and experiencing seasons that last over twenty years, the temperature differences on the summer and winter sides of the planet do not differ that greatly. Near the cloudtops, the temperature of Uranus is near -215 C.

Uranus' rings were first discovered in 1977. The rings are in the planet's equatorial plane, perpendicular to its orbit about the Sun. The 10 outer rings are dark, thin, and narrow, while the 11th ring is inside the other ten and is broad and diffuse. The rings of Uranus are very different from those surrounding Jupiter and Saturn. When viewed with the Sun behind the rings, fine dust can be seen scattered throughout all of the rings.

Uranus is named for an ancient Greek sky god. It has 27 known moons, named mostly for characters from the works of Shakespeare and Alexander Pope. Miranda is the strangest Uranian moon. The high cliffs and winding valleys of the moon may indicate partial melting of the interior, with icy material occasionally drifting to the surface.


Uranus: Facts & Figures

Discovered By: William Herschel

Date of Discovery: 1781

Average Distance from the Sun

Metric: 2,870,972,200 km

English: 1,783,939,400 miles

Scientific Notation: 2.8709722 x 109 km (19.191 A.U.)

By Comparison: 19.191 x Earth


Perihelion (closest)

Metric: 2,735,560,000 km

English: 1,699,800,000 miles

Scientific Notation: 2.73556 x 109 km (18.286 A.U.)

By Comparison: 18.60 x Earth


Aphelion (farthest)

Metric: 3,006,390,000 km

English: 1,868,080,000 miles

Scientific Notation: 3.00639 x 109 km (20.096 A.U.)

By Comparison: 19.76 x Earth


Equatorial Radius

Metric: 25,559 km

English: 15,882 miles

Scientific Notation: 2.5559 x 104 km

By Comparison: 4.007 x Earth


Equatorial Circumference

Metric: 160,592 km

English: 99,787 miles

Scientific Notation: 1.60592 x 105 km


Metric: 69,142,000,000,000 km3

Scientific Notation: 5.9142 x 1013 km3

By Comparison: 63.1 x Earth



Metric: 86,849,000,000,000,000,000,000,000 kg

Scientific Notation: 8.6849 x 1025 kg

By Comparison: 14.371 x Earth's



Metric: 1.30 g/cm3

By Comparison: 0.236 x Earth


Surface Area

Metric: 8,115,600,000 km2

English: 3,133,400,000 square miles

Scientific Notation: 8.1156 x 109 km2

By Comparison: 15.91 x Earth


Equatorial Surface Gravity

Metric: 8.43 m/s2

English: 27.7 ft/s2

By Comparison: If you weigh 100 pounds on Earth, you would weigh 86 pounds on Uranus.


Escape Velocity

Metric: 76,640 km/h

English: 47,620 mph

Scientific Notation: 21,290 m/s

By Comparison: 1.904 x Earth


Sidereal Rotation Period (Length of Day)

-0.7196 Earth days (retrograde)

-17.24 hours (retrograde)

By Comparison: 0.722 x Earth


Sidereal Orbit Period (Length of Year)

84.02 Earth years

30,687.2 Earth days

Mean Orbit Velocity

Metric: 24,607 km/h

English: 15,290 mph

Scientific Notation: 6,835.2 m/s

By Comparison: 0.229 x Earth


Orbital Eccentricity


By Comparison: 2.823 x Earth


Orbital Inclination to Ecliptic

0.770 degrees

Equatorial Inclination to Orbit

97.86 degrees

By Comparison: 4.173 x Earth


Orbital Circumference

Metric: 17,620,000,000 km

Scientific Notation: 1.762 x 1010 km

By Comparison: 19.06 x Earth


Effective Temperature

Metric: -216 C

English: -357 F

Scientific Notation: 57 K

Atmospheric Constituents

Hydrogen, Helium, Methane

Scientific Notation: H2, He, CH4

By Comparison: Earth's atmosphere consists mostly of N2 and O2.


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