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2.9 billion kilometres away from the sun is the fourth largest planet in our solarsystem. Discovered by William Herschel in 1781 this planet displays some remarkable features. Not only does this gas giant also have a ring system (though very small compared to Saturn) consisting of atleast 11 rings, but its axis of spinning is tilted 98 degrees, suggesting a giant impact in its early history. This tilting gives rise to a summer season lasting half ( = 42 years) its orbit and a winter season lasting equally as long. Though the polar zones receive more radiation from the sun, the equatorial areas are hotter. The reason is unknown.
Like the other four gas giants, (the jovian planets: Jupiter, Saturn, Uranus and Neptune) Uranus radiates more heat into space than it receives from the sun. This could mean that the planet is still somehow contracting since its formation. Its thought to have a rocky core.
So far the only spacecraft that has visited Uranus is Voyager 2, in 1986. Then Uranus displayed very little features in its cloudy atmosphere. Voyager 2 then detected a magnetic field from the planet.

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Uranus's Orbit - Space Art
Uranus's Ring System - Space Art

The Moons

Uranus has many moons (atleast 27). Most of these are captured asteroids as they are small in size and irregular in shape. The five main satellites are Miranda, Ariel, Umbriel, Titania and Oberon. They are all named from characters in William Shakespeares work. In the space art to the right you can see ten rings of Uranus as well as the moon Cordelia, which is about 15 km in diameter and depicted from a distance of 3 000 km. It is the innermost moon of Uranus and it orbits in the ring system at a distance of about 24 000 km from the surface.

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The Ring System

Uranus' rings were discovered in 1977 when two astronomers were observing a uranus was supposed to occult (pass in front of) a star. When Uranus occulted the star it appeard to "blink" several times, leading to the conclusion that Uranus had rings. When Voyager 2 arrived at Uranus more rings (actually Uranus has many rings or ringlets) and moons were discovered.
The outermost, which is called the "epsilon ring", is composed mostly of ice boulders several feet across and is mostly grey in colour. The moons Cordelia (inside the ring) and Ophelia (outside the ring) act as shepherd satellites for the epsilon ring. A shepherd moon is a moon that orbits near the edge of a planetary ring, constraining the ring's extent through gravitational pull. Saturn is known to have many of those. The ring system is actually composed of small objects, rarely larger than 10 metres across. Please see the right for space art of Uranus ring system.

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Previous: Saturn.
Next: Neptune.


Moons: 27.
Average distance from sun:
2 870 972 200 km.
Equatorial Radius: 25 559 km.
Mass: 8.6849 x 10^25 kg.
Density: 1.30 g/cm^3.
Escape Velocity: 21.290 km/s.
Length of day: -17.24 hours (retrograde).
Length of year: 84.02 Earth years.
Mean Orbit Velocity: 6.835.2 km/s.
Equatorial Inclination to Orbit: 97.86 degrees.
Effective Temperature: -216 C.
Atmosphere: Hydrogen 83%, Helium 15%, Methane 2%.
Misc: Discovered by William Herschel in 1781.

Source: NASA.

Space art: Neptune

Space Art 1: Uranus seen with ten of its eleven rings. The moon Cordelia is visible in the ring system.


All content Copyright , 2005- by Fahad Sulehria, unless stated otherwise.
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