Uranus
Planet
Facts
- Diameter
- 51,118 km
- Mean distance from the Sun
- 2.87 billion km
- Orbital period
- about 84 years
- Rotation
- 17.2 hours, backwards
- Axial tilt
- 97.8°
- Minimum temperature
- −224 °C, in the atmosphere
Uranus is the seventh planet from the Sun, an ice giant: most of its mass is a dense fluid of water, methane and ammonia above a small rocky core. Methane in the atmosphere gives it its blue-green colour. It is named after the Greek god of the sky.
It spins almost lying on its side: each pole in turn is lit for a long time, while the other half of the planet stays in a dark winter lasting 21 years. At the equator the winds blow against the planet's rotation. It has 13 faint rings.
William Herschel discovered it in 1781 while searching for faint stars: it was the first planet found with a telescope and the first new planet since antiquity. In 1977, watching Uranus pass in front of a distant star (an occultation), astronomers found that it has rings too. On 24 January 1986 Voyager 2 became the first and so far only probe to visit it, finding 10 new moons and two new rings.