Uranus
What is Uranus?
Planets· Diameter 50,724 km. An ice giant that circles the Sun lying on its side, its axis tilted 98 degrees, so each pole gets 42 years of daylight followed by 42 years of night. Voyager 2, in 1986, is the only spacecraft to have visited.
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Orbit and size
| Diameter | 50,724 km |
|---|---|
| Distance | 19.2 AU |
| Year | 84 yr |
| Tilt | 98° (on its side) |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Moons of Uranus
How George's Star came to be called Uranus
When Herschel discovered the planet in 1781, he named it 'George's Star' after his patron, King George III of Britain. Outside Britain the name was not accepted, and in France the planet was sometimes called 'Herschel' after its discoverer. For a while the same planet went by different names in different countries.
The name we use today was proposed by the German astronomer Johann Bode. He suggested following the family tree of mythology: Saturn is the father of Jupiter, so the next planet out should be named after Saturn's father, the sky god Uranus. The name gradually spread, and Britain's official Nautical Almanac adopted it in 1850. That is why Uranus is the only planet named after a Greek god rather than a Roman one.
Uranus had been recorded many times before its discovery. In 1690 the English astronomer John Flamsteed listed it as a star, 34 Tauri. The French astronomer Pierre Le Monnier noted it twelve times between 1750 and 1769 without realizing it was a planet. These old records were later used to work out Uranus's orbit precisely.
The planet in depth
Uranus's axis is tilted 98 degrees, so it rolls around the Sun lying on its side. Why it tipped over is not certain, but the most widely accepted idea is that a large body struck it while it was forming. The tilt gives it extreme seasons. Uranus takes 84 years to circle the Sun, and for about 42 of them one pole never sees the Sun set, while for the other 42 it stays in darkness.
William Herschel found Uranus with a telescope in 1781. Every planet known before then could be seen with the naked eye, so Uranus was the first planet discovered by telescope. It is actually just bright enough to glimpse without one under a very dark sky, but it moves so slowly that it was hard to tell apart from a star.
Uranus looks blue-green because of methane in its atmosphere. Methane absorbs the red part of sunlight, and the remaining blue and green light is reflected back to us. Uranus has 13 known rings, but they are made of dark particles and are much fainter than Saturn's. The orbit view shows the rings together with the planet's tipped axis.
Apart from Voyager 2's single flyby in 1986, no spacecraft has visited Uranus, so much about it is still unknown. In 2022 the US planetary science community recommended an orbiter with an atmospheric probe as the top priority for its next large mission. If it goes ahead, it will give Uranus and its moons their first long, careful look.
Frequently asked
- How big is Uranus?
- The diameter of Uranus is 50,724 km.
- How far is Uranus from Earth?
- The distance of Uranus is 19.2 AU.
- What are the main moons of Uranus?
- The main moons of Uranus are Titania, Oberon, Miranda, Ariel, Umbriel.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.