Uranus is the third largest planet in the Solar System by size, and fourth largest by mass. It is the seventh planet from the Sun. It is very similar to Neptune in composition, and almost identical in size. So what do we know about this bland-looking planet?

Atmosphere

Uranus is very similar in composition to Neptune. Both are composed of Hydrogen and Helium in the upper atmosphere, and "ices" of ammonia, methane, water, along with a small percentage of hydrocarbons, deeper into the atmosphere. It is the coldest planet in the Solar System, even colder than Neptune, with temperatures going down to 224C. It is encircled by a small number of clouds. The lower clouds are believed to be made up of water; the upper clouds - of methane. The wind speeds on Uranus can reach 560 mph. And you thought Earth's tornado's were bad!

Discovery

Sadly, just like all the other planets, this planet was named after a mythical god, the Greek god of sky. The official discoverer of the planet opted to call it the "Georgian planet" in honor of his patron King George III, and to break away from the track record of naming every planet after mythical gods. But the idea was not supported outside of Britain. So the legacy continued.

Orbit and Rotation

Uranus orbits the Sun in 84 Earth days. It gets only about 1/400 of sunlight than we do. The interior of Uranus takes 17 hours, 14 minutes to rotate, and the outer atmosphere takes as little as 14 hours. This is due to the fact that Uranus experiences very strong winds in the upper atmosphere in the direction of its rotation, causing the gasses in the upper atmosphere to move faster than the planet's interior.

Seasons and Days

Uranus is tilted at 97.77, making its axis of rotation almost parallel to the plane of the Solar System. This results in very different seasonal and day/night changes than on other major planets. Instead of Sun shining on the equators, like on other planets, the Sun shines on the North and South poles. This causes nights to last for 42 years at each pole, followed by a 42-year day when the planet goes to the other side of the Sun. The orbit of the planet can be visualized as a rolling ball going around the Sun. Only a narrow strip near the equator experiences rapid night/day changes. But even those days don't seem like much of a day. At the equator, the Sun would rise a little bit above the horizon and than go back very quickly.Uranus Ring Diagram

The reason for such an unusual axis tilt is not known. A change in tilt could have occurred some time in the past, caused by a collision with other space objects. But it could have had this tilt since creation. You know, God didn't have to create every planet the same way.

Planetary Rings

Uranus has a complicated system of planetary rings. Those rings are made up of extremely dark particles ranging from micrometers to a fraction of a meter. Most of these rings are only a few kilometers wide. The diagram on the right illustrates the current model of the ring system around Uranus.

Magnetic Field

The magnetic field of Uranus has a unique twist to it. Unlike Earth's magnetic field, where the magnetic poles closely correspond with the physical poles, Uranus's magnetic field is at 59 to its axis of rotation. The strength of magnetic field at the northern hemisphere can be up to 11 times stronger than in the southern hemisphere. So if you tried navigating the "oceans" of Uranus with a compass, the North arrow would lead you quite a bit away from the north pole.

Climate

When Voyager 2 spacecraft flew by Uranus in 1986, it observed ten cloud features across the entire planet. A Uranus dark spot was discovered in 2006, similar to the Dark Spot on Neptune.

Winds on Uranus very depending on the location. At the equator, winds blow at speeds of 50-100 m/s in the direction opposite to planet's rotation. As you go away from the equator, wind speeds slow down, and stop at 20 latitude. Closer to the poles, the winds shift to the same direction with planet rotation. At around 60 latitude they become the fiercest, blowing at speeds of up to 240 m/s. At the poles winds halt again.

Extreme seasonal variations have been observed on Uranus. For example, for a period from March to May 2004, Uranus behaved much like Neptune. Formation of large cloud regions, violent winds reaching 824 km/h, and a persistent thunderstorm, led astronomers to call this event the "Fourth of July Fireworks".

Moons

Uranus has 27 known moons. These moons were named after characters in the works of Shakespeare and Alexander Pope. The five major moons are called Miranda, Ariel, Umbriel, Titania and Oberon. Their images are included below. The largest of these, Titania, is only half the size of our moon. They are believed to be composed of ice and rock. Miranda has craters up to 20 km deep.

Sources:

http://wikipedia.com/uranus



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