English astronomer William Herschel discovered Uranus in 1781.
It was the first planet discovered that is not easily visible
with the naked eye. It lies twice as far from the Sun as Saturn.
Uranus is unusual because it spins on an axis tilted at 98° and
so appears to spin on its side. This may be because Uranus
collided with another large object as it was forming. Table 16.
ESSENTIAL DATA |Diameter at equator||51,118 km (31,764 miles)|
|Average distance from Sun||2,871 million km (1,784 million
miles)| |Orbital period||84 years| |Rotation period||17.24
hours| |Cloud-top temperature||-197°C (-323°F)| |Number of
moons||22| The rings of Uranus were discovered in 1977. As the
planet passed in front of a star the rings could be seen against
the bright background. In 1986, Voyager 2 imaged the rings and
11 were identified. The atmosphere of Uranus is a greenish-blue
colour. It is almost completely featureless in ordinary light.
There are no signs of the cloud bands visible on Jupiter and
Saturn. In all, Uranus has