Uranus is the seventh planet from the sun and was the first to be discovered with the use of a telescope by William Herschel in 1781. It is barely visible to the naked eye and through a telescope it looks like a green-colored disc. Except for Saturn, Uranus is the only other planet in the solar system that has rings.
Of the four so-called giant planets (Jupiter, Saturn and Neptune), Uranus has the smallest mass. However, this mass is still about 14.5 times that of Earth. Its diameter is 48,000 km. which is a little over three times that of the diameter of the Earth, but its density is only about a third of that of the Earth. The atmosphere around Uranus is believed to contain methane, hydrogen and helium. Scientists are unsure of the composition of the core of the planet, but believe that it contains large amounts of ammonia, solid ice, methane and some of the heavier elements. The surface temperature is about -184C.
The distance from the sun to Uranus is about 19 times that of the Earth. It takes 84 years for the planet to make one full revolution around the sun and it rotates on its axis once every 10.75 hours. The equator of this planet is almost at right angles to the plane of its axis, making it the only planet to have an equator that incline more than 30 to its orbit. The rotation is also in the opposite direction from its revolution around the sun and in this way the planet is similar to Venus.
In 1976, it was discovered that there were rings around Uranus. They consist of numerous boulders and are believed to lie in a band that is about 18,000 to 20,000 km above the atmosphere of the planet. It also has five large satellites, or moons, that lie in the same plane as the equator. They revolve in the same direction as the planet's rotation patterns. Although each of these satellites are several hundred miles in diameter, they revolve around Uranus once every few days.
When William Herschel discovered Uranus in 1781, he thought that what he was seeing in the sky was a new comet. Upon further inspection and continued observations he came to the conclusion that it was a planet. After he published his findings and they were proved to be correct, it was revealed that this planet had been observed about 20 times before that and those who did so had no idea that they were observing a planet of the solar system. It was through close study of the revolution of Uranus around the sun that led to the discovery of another planet - that of Neptune.