Uranus

Uranus (also spelled Uroono) is the seventh planet from the Sun. It is a large gas and ice giant with no solid surface to stand on. Its equatorial diameter is significantly larger than Earth's, but smaller than Jupiter and Saturn.

Uranus is classified as one of the "ice giants," a category it shares with Neptune. This is because its lower layers are composed of dense materials such as water, ammonia, and methane under high temperatures and pressures, whereas Jupiter and Saturn are primarily hydrogen and helium.

Discovery

Uranus is the first planet to have been discovered by telescope, identified by astronomer William Herschel in 1781. Before that time, people could see only six planets close to the Sun with the naked eye. Uranus can sometimes be seen without a telescope, but its light is very faint, so in earlier times it was mistaken for a star.

Orbit and rotation

The most distinctive feature of Uranus is that its axis of rotation is extremely tilted, nearly lying on its side relative to its orbit around the Sun. This causes extreme seasonal variations on the planet: each hemisphere receives prolonged sunlight followed by a prolonged period of darkness. It takes approximately 84 Earth years to orbit the Sun.

Atmosphere and color

Uranus's atmosphere is composed mainly of hydrogen and helium, with some methane. The methane absorbs red light, which is why the planet appears blue-green in color. The upper atmosphere is extremely cold, making it one of the coldest places in the solar system.

Rings and moons

Uranus has a system of faint, dark rings that are difficult to observe, unlike Saturn's prominent ring system. It also has many moons, the largest of which are Titania, Oberon, Umbriel, Ariel, and Miranda. The moons are named after characters from English literature, particularly Shakespeare.

Exploration

So far only one spacecraft has passed close to Uranus and conducted detailed observations: Voyager 2, which flew past in 1986. Much additional data has been gathered from Earth-based telescopes and space telescopes such as Hubble. Many scientists have proposed that a new mission is needed to conduct a direct study of Uranus.