Introduction

Uranus is the seventh planet from our sun and the third in a line of four gas giants; it is four planets outward from Earth. Uranus is about 1.78 billion miles (2.86 billion miles) from the sun, more than twice as far from the sun as its closest neighbour, Saturn. Thus, the discovery of Uranus doubled the known size of the solar system. Uranus is 31,800 miles (51,166 kilometers) in diameter at its equator, making it the third largest planet in the solar system. It is four times the size of Earth, yet less than half the size of Saturn. Similar to Jupiter, Saturn, and Neptune, Uranus consists mostly of gas. Its pale blue-green, cloudy atmosphere is made of 83 percent hydrogen, 15 percent helium, and small amounts of methane and hydrocarbons. Uranus gets its color beacause the atmospheric methane absorbs light at the red end of the visible spectrum and reflects light at the blue end. Deep down into the planet, a slushy mixture of ice, ammonia, and methane surrounds a rocky core. Uranus is surrounded by fifteen moons and eleven rings.

Who discovered the planet Uranus?

German astronomer William Herschel (1738-1822), who lived and worked in England, was conducting a general survey of the stars and planets in 1971 when he observed a disk-shaped object in the constellation Gemini. At first Herschel thought the ocject was a comet. But its orbit was not aselongated as a comet's; it was more circular, like that of a planet. Six months later he became convinced that this body was indeed a planet, Uranus. HE calculated its orbit and found its was twice as far from the sun as the closest planet, Saturn. The new planet was given two tentativ names before astronomers decided to called it Uranus, the mythological father of Saturn. Upon confirmation that he had discovered a new planet, Herschel was made a member of the prestigious British science club called the Royal Society. The discovering also came to the attention of England's King George III, who appointed Herschel to be the KIng's Astronomer. The position included a small salary, which enable Herschel to study the skies full time. Working alongside his sister, astronomer Caroline Herschel made contributions to our understanding of stars, nebulae, the Milky Way, asteroids, the sun, and our solar system. Herschel came to believe that other solar systems outside our own may exist. He challenged the popular notion that the Milky Way was the center of the universe and suggested that our galaxy, and Earth itself, were quite insignificant pieces of an immense puzzle.

What is the nature of Uranus's rings?

The first nine rings of Uranus were discovered only nine years before Voyager 2's visit. We now know that Uranus is surrounded by eleven rings plus ring fragments, consisting of dust, rocky particles, and ice. The eleven rings occupy the region between 23,560 and 31,700 miles (38,000 and 51,000 kilometers) from the planet's center. Each ring is anywhere from less than a mile to 1,550 miles (0.5 to 2,5000 kilometers) wide. The outermost ring, called the epsilon ring, is only several feet across and is made up of ice boulders. The pressure of ring fragments indicate that the rings are may be younger than the planet they encircle. One theory suggests that the rings are made of fragments of a moon that was smashed to pieces.

Why do days last forty-two Earth years on Uranus?
Uranus rotates on its side, so that one of its poles faces toward the sun throughout half of its eighty-four year orbit, while the other leg of its journey, the other pole faces the sun for forty-two Earth years. At some point in its history, Uranus was probably struck by a large object that knocked it sideways. As a result, its equator lies on a plane perpendicular to the plane of the planets' orbits. In contrast to Uranus, the Earth is positioned nearly upright. Our equatorial plane lies almost parallel to the plane of our orbit around the sun, so our entire planet experiences both night and day in every twenty-four hour period.

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