Uranus

**Uranus** is the seventh planet from the Sun in our Solar System. Like Neptune, it is an ice giant. It is the third largest planet in the solar system.

The planet is made of ice, gases and liquid metal. Its atmosphere has hydrogen, helium and methane. The temperature on Uranus is  near the top of its atmosphere. Its small solid core (about 55% the mass of Earth) is probably about .

The planet is tilted on its axis so much that it is sideways. Nobody knows why exactly it is. It has five big moons, many small ones, and a small system of 13 planetary rings.

The distance between Uranus and the Sun is about 2.8 billion km. Uranus completes its orbit around the Sun in 84 earth years. It completes a spin around its axis in 17 hours and 14 minutes. This means there are about 43,000 days in a year on Uranus.

Uranus was discovered in 1781. This planet can be seen with the naked eye under perfect conditions. John Flamsteed saw it decades before but thought it was a star (34 Tauri).

Near the solstice, one pole faces the Sun continuously and the other faces away. Only a narrow strip around the equator has a rapid day–night cycle, with the Sun low over the horizon. Each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness.

Uranus is named after Uranus, the Greek mythology version of the Sumerian god Anu, who was a god of the sky.

## History 
### Discovery 
Uranus has been seen many times through a telescope, and even sometimes without any, but people thought it was a star due to its slow orbit. Sir William Herschel observed Uranus on March 13, 1781 from the garden of his house at 19 New King Street in Bath, Somerset, England (now the Herschel Museum of Astronomy), and first said it was a comet (on April 26, 1781). With a homemade 6.2-inch reflecting telescope, Herschel "engaged in a series of observations on the parallax of the fixed stars."

Herschel wrote in his journal: "In the quartile near ζ Tauri... either [a] Nebulous star or perhaps a comet." 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." When he presented his discovery to the Royal Society, he continued to assert that he had found a comet, but also implicitly compared it to a planet:

Although Herschel continued to say this new object was a comet, other astronomers had already begun to think otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to calculate the orbit of the new object. Bode concluded that its near-circular orbit was more like a planet's than a comet's.

The object was soon widely accepted as a new planet. By 1783, Herschel acknowledged this to Royal Society president Joseph Banks: "By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honor of pointing out to them in March 1781, is a Primary Planet of our Solar System."

## Features 
### Moons 
Uranus has 27 known moons. They are named for characters from the works of Shakespeare and Alexander Pope. The five biggest moons are Miranda, Ariel, Umbriel, Titania and Oberon. It is likely that more moons will be found.

### Clouds 
Uranus is covered in blue clouds. The top clouds, made of methane, are hard to see. Lower clouds are thought to be frozen water. There are also violent storms. Wind speeds can reach . Scientists are studying the clouds to try to understand the storms on the planet.

### Rings 
The planet **Uranus** has a system made of **13 rings**, which is far fewer than the rings of Saturn but more than those around Jupiter and Neptune. The rings of Uranus were discovered in 1977. More than 200 years ago, William Herschel also said he saw rings, but today astronomers do not believe that he saw them, because they are very dark and hard to see. Two inner rings were discovered in 1986 in images taken by Voyager 2, and two outer rings were found in 2003–2005 by the Hubble Space Telescope. The rings are probably made of ice.

A lot of people think the rings of Uranus are quite new. They say that the rings are less than 600 million years old. The planet's ring system probably came from when some of its moons crashed together. After crashing, the moons probably broke up into many small pieces of rock and ice, which orbited Uranus and turned into rings.

#### General properties 
The ring system of Uranus has thirteen rings. In order of how close they are to Uranus, the rings are 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. There are three groups: nine small 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 (or visible) particles and less dust, although people know dust is in 1986U2R/ζ, η, δ, λ, ν and μ rings.

There also may be a lot of thin dust bands and faint rings between them. These faint rings and dust bands may stay for only a short time. Some of them became visible during a series of ring events in 2007 when the rings were at different angles. Many dust bands between the rings were seen by *Voyager 2*. All rings of Uranus have different brightnesses.

The rings are made of somethng that is super dark. The rings are slightly red in the ultraviolet and visible parts of the spectrum and grey in near-infrared. 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. So they are probably a mixture of ice and a dark material. It is hard to know what this material is, but scientists think it may be organic compounds that were darkened by charged particle irradiation from the planet's magnetosphere. The rings' particles may by made of a crushed material, which the inner moons used to be made of. Its orbital elements were first calculated in 1783 by Pierre-Simon Laplace. With time, changes began to appear between the predicted and observed orbits, and in 1841, John Couch Adams first said that the differences might be because of the gravity of another planet. In 1845, Urbain Le Verrier began his own independent research into Uranus's orbit. On September 23, 1846, Johann Gottfried Galle found a new planet, later called Neptune, close to the area Le Verrier said it would be.

The time it takes for the inside of Uranus to spin around itself is 17 hours and 14 minutes, clockwise (retrograde). Like all giant planets, its upper atmosphere has very strong winds in the direction that the planet rotates. At some latitudes, such as about two-thirds between the equator and the south pole, the parts of the atmosphere we can see move much faster, making a full rotation in just 14 hours.

## Related pages
* List of planets

## References 
### Notes
## Other websites 
* NASA's Uranus fact sheet 
* Uranus Profile  by NASA's Solar System Exploration
* Keck pictures of Uranus show best view from the ground  — Press release with some photographs showing rings, satellites and clouds
* 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.
* [Uranus (planet)](http://en.citizendium.org/wiki/Uranus_(planet)) -Citizendium