Uranus is the seventh planet from the Sun, named after the ancient Greek deity of the sky, the father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Uranus was the first planet discovered in modern times by Sir William Herschel on 13 March 1781.
Uranus and Neptune have different internal and atmospheric compositions from those of the larger giants and astronomers sometimes place them in a separate category - 'ice giants.' Uranus' atmosphere is composed primarily of hydrogen and helium, and contains a higher proportion of water, ammonia and methane, along with traces of hydrocarbons. It is the coldest planetary atmosphere in the Solar System.
Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways.
This wider view of Uranus reveals the planet's faint rings and several of its satellites. The area outside Uranus was enhanced in brightness to reveal the faint rings and satellites. The outermost ring is brighter on the lower side, where it is wider. It is made of dust and small pebbles, which create a thin, dark, and almost vertical line across the right side of Uranus (especially visible on the natural-colour image). The bright satellite on the lower right corner is Ariel, which has a snowy white surface. Five small satellites with dark surfaces can be seen just outside the rings. Clockwise from the top, they are: Desdemona, Belinda, Portia, Cressida, and Puck. Even fainter satellites were imaged in deeper exposures, also taken with the Advanced Camera in August 2003.