Uranus is the seventh planet from the sun. Its average distance from the sun is about 1.8 billion miles. Uranus was discovered in 1781 by William Hershel. It is 31,945 miles in diameter. Uranus's day is 17 hours and 12 minutes. Uranus's year is about 84 Earth years long, and sometimes during the orbital period, Uranus's south and/or north poles are in total darkness. This is caused by Uranus's axial tilt of 977.9*, which makes it look like it is lying on its side as it rotates. Uranus's Interior and Atmosphere Like Saturn and Jupiter, some scientists believe that Uranus has a core of melted rock. Other's think that Uranus has a solid core. Surrounding the core is a mantle (layer) of liquid hydrogen, what is covering this mantle is unknown. Some scientists believe that there is an "ocean" made of water, methane, and ammonia.
The clouds covering Uranus are probably made of helium, hydrogen, and methane. Unlike the clouds on the three other gas giants though, Uranus's clouds don't form bands. In fact, Uranus has no features at all, the clouds appear to be just a blue-green mass. Some say the blue-green mass is a frozen layer of methane floating above the other clouds. While no storms like Jupiter's Great Red Spot have been seen on Uranus, there are winds that do reach over 370 miles per hour. These winds are probably caused by Uranus's fast rotation. Some slight surface features have been photographed by the Hubble Telescope, but Uranus is still the planet with the least surface features. Uranus's Rings Uranus's rings were first seen in 1977 by some astronomers observing Uranus pass in front of a star. The star kept getting brighter and dimmer and so on when Uranus got closer to it. When the star got on the side of Uranus, the same thing happened. The changes in the brightness in the star was being blocked by something --- Uranus's rings. The pictures of Uranus's rings that were sent back by Voyager 2 were spectacular. Uranus's rings are completely different from the ones around Saturn and Jupiter. There are 11 rings in all, varying in size from 6 to 60 miles wide. They are made of charcoal-colored rocks and tiny, dust-sized particles. Just like Saturn's rings, some of Uranus's rings are held together by small shepherd moons (see Saturn for meaning of shepherd moons). Uranus's Moons Uranus has 15 moons in all, the five largest and farthest from Uranus are all more than 200 miles in diameter, but none of the other moons' diameters are more than 100 miles. Oberon, Titania, Ariel, Umbriel, and Miranda are the largest of the moons and are all made up of mainly ice and rock. They are all heavily cratered and dark, probably because there might be a lot of dirt on their surfaces. Miranda has more varied features than any celestial body seen. Miranda has craters and also a grooved terrain. One looks like a huge running track, and another looks like a dark-colored chevron. Another strange feature on Miranda is a set of ice cliffs. These ice cliffs still remain a mystery. Titania is the largest of Uranus's moons, and its surface has many valleys. Oberon is similar in size to Titania. Ariel and Umbriel are almost the same size, but they are very different. Umbriel is very dark and has many craters. Ariel doesn't have as much craters, but instead, it has lots of valleys like Titania.
