Uranus

Uranus

2,870,990,000 km (19.218 AU) from the Sun, Uranus hangs on the wall of space as a mysterious blue green planet. With a mass of 8.683e25 kg and a diameter of 51,118 km at the equator, Uranus is the third largest planet in our solar system. It has been described as a planet that was slugged a few billion years ago by a large onrushing object, knocked down (never to get up), and now proceeds to roll around an 84-year orbit on its belly. As the strangest of the Jovian planets, the description is accurate. Uranus has a 17 hour and 14 minute day and takes 84 years to make its way about the sun with an axis tilted at around 90° with retrograde rotation. Stranger still is the fact that Uranus' axis is almost parallel to the ecliptic, hence the expression "on its belly".

Uranus is so far away that scientists knew comparatively little about it before NASA's Voyager 2 undertook its historic first encounter with the planet. The spacecraft flew closely past distant Uranus, and came within 81,500 kilometers (50,600 miles) of Uranus's cloudtops on Jan. 24, 1986. Voyager 2 radioed thousands of images and mass amounts of other scientific data about Uranus, its moons, rings, atmosphere, interior and magnetic environment. However, while Voyager has revealed much about the gas giant, many questions remain to be answered.

The history of the planet's discovery is the first we have of its kind; Uranus was the first planet to be discovered with a telescope. The circumstances surrounding the discovery of the object are befitting of the odd planet. The earliest recorded sighting of Uranus was in 1690 by John Flamsteed, but the object was catalogued as another star. On March 13, 1781 Uranus was sighted again by amateur astronomer William Herschel and thought to be a comet or nebulous star. In 1784, Jean-Dominique Cassini, director of the Paris Observatory and prominent professional astronomer, made the following comment:

'A discovery so unexpected could only have singular circumstances, for it was not due to an astronomer and the marvelous telescope…was not the work of an optician; it is Mr. Herschel, a [German] musician, to whom we owe the knowledge of this seventh principal planet.' (Hunt, 35)

Four years passed before Uranus was recognized as a new planet, the first to be discovered in 'modern' times.