Hugo's Solar System
Planet
Uranus
The pale blue-green ice giant that rolls around the Sun on its side
"I roll on my side," says Uranus, quite proud.
"My spin is peculiar and wows every crowd."From Hugo's Journey Through Space
Key facts
- Diameter
- 31,800 miles / 51,118 km at the equator (about four times Earth)
- Distance from the Sun
- About 19 AU (about 1,800 million miles / 2,900 million km)
- One orbit
- About 84 Earth years
- One day (rotation)
- About 17 hours
- Axial tilt
- 97.77 degrees, so it spins almost on its side
- Average temperature
- About -214 °C (effective); the atmosphere has been measured as cold as -224 °C
- Known moons
- 29 (as of September 2026)
- Rings
- 13 faint rings
- Named after
- Uranus, the Greek god of the sky, a name suggested by Johann Bode
- Discovered
- 13 March 1781 by William Herschel, in Bath, England
- Visited by
- Voyager 2 only, flying past on 24 January 1986
- Mass
- About 86.8 million million million million kg (8.68 × 10^25 kg)
About Uranus
Uranus is a big blue-green planet. It is very far from the Sun. It is cold and windy there. Uranus is made mostly of gas and ice. You could not stand on it. Here is a funny thing. Uranus spins on its side. It rolls round the Sun like a ball. A year on Uranus is very long. It lasts about 84 Earth years. Uranus has thin, dark rings. It has 29 moons that we know of. Only one spacecraft has ever seen it up close. That was Voyager 2, long ago.
Uranus is the seventh planet from the Sun, an ice giant. It is about four times wider than Earth, a pale blue-green sphere. Its diameter is about 51,118 kilometres across the equator. Uranus sits about 19 times further from the Sun than Earth does.
Sunlight takes about 2 hours and 40 minutes to reach it. One orbit around the Sun takes about 84 Earth years. Yet Uranus rotates quickly, so one day lasts only about 17 hours. The strangest thing about Uranus is its axis, which is tilted almost 98 degrees.
This means the planet spins on its side, like a rolling ball. Each pole gets about 42 years of sunlight, then 42 years of darkness. The atmosphere is mostly hydrogen and helium, with a little methane. Methane absorbs red light, which gives Uranus its blue-green colour.
Winds there can blow at about 900 kilometres per hour. Beneath the clouds lies a hot, dense fluid of water, methane and ammonia. Uranus has 13 known rings and 29 known moons as of August 2026. The moons are named after characters from Shakespeare and Alexander Pope.
William Herschel discovered Uranus in 1781 using a telescope he built himself. Only Voyager 2 has visited, flying past in January 1986.
Uranus is the seventh planet from the Sun and, with Neptune, an ice giant. Its equatorial diameter is 51,118 km, about four times Earth's, and it orbits at roughly 19 astronomical units (about 2.9 billion km), so sunlight takes about 2 hours 40 minutes to arrive. One orbit takes 84 Earth years; one rotation takes about 17 hours. The atmosphere is mostly hydrogen and helium with a small amount of methane, which absorbs red light and produces the planet's blue-green colour. Beneath it, NASA describes 80 per cent or more of the planet as a hot, dense fluid of water, methane and ammonia above a small rocky core, where temperatures reach about 4,982 °C. Winds run up to 900 km/h.
The defining feature is the axial tilt of 97.77 degrees, so Uranus rotates nearly at right angles to its orbit and each pole receives about 42 years of continuous sunlight followed by 42 years of darkness. Some references quote 82.23 degrees with retrograde rotation; that is the same orientation described by a different convention, not a disagreement about the planet. The magnetic field is also odd: its axis is tilted nearly 60 degrees from the rotation axis and offset from the centre by about a third of the planet's radius.
Uranus is commonly called the coldest planet. Neptune is further from the Sun, but the lowest temperature measured in any planetary atmosphere, 49 K (minus 224 °C), belongs to Uranus, so the claim is correct in that specific sense. Its effective temperature is about 59 K.
William Herschel discovered Uranus on 13 March 1781 from his garden in Bath, at first reporting it as a comet. Earlier observers, including John Flamsteed in 1690, had catalogued it as a star. Herschel proposed Georgium Sidus after George III; Johann Bode's choice, Uranus, the Greek sky god and father of Saturn, became universal by 1850.
Voyager 2 remains the only spacecraft to visit, passing 81,500 km from the cloud tops on 24 January 1986. It found ten new moons and two new rings, bringing the current totals to 13 rings and, as of August 2026, 29 known moons, named for characters from Shakespeare and Alexander Pope. The 2023 to 2032 Planetary Science Decadal Survey named a Uranus Orbiter and Probe as its top-priority flagship mission, but none has launched.
Did you know?
- Uranus was nearly called Georgium Sidus, or George's Star, after King George III. The name Uranus only became standard in 1850.
- The magnetic field of Uranus is tilted nearly 60 degrees from its spin axis and does not even pass through the planet's centre.
- Uranus has the coldest measured atmosphere of any planet, at minus 224 °C, even though Neptune is further from the Sun.
Moons of Uranus
Uranus has 29 known moons as of September 2026. The largest are listed here; the other 2 are smaller moons, most only a few kilometres across. How many moons does Uranus have?
- Titania
- Oberon
- Umbriel
- Ariel
- Miranda
- Puck
- Sycorax
- Portia
- Juliet
- Belinda
- Cressida
- Rosalind
- Caliban
- Desdemona
- Bianca
- Prospero
- Setebos
- Ophelia
- Cordelia
- Stephano
- Perdita
- Francisco
- Ferdinand
- Margaret
- Trinculo
- Mab
- Cupid
Questions children ask
Why does Uranus spin on its side?
Nobody knows for certain. Its axis is tilted by 97.77 degrees, and the most popular idea is that a giant object about the size of Earth crashed into the young planet, knocking it over. Scientists are still testing this with computer models.
Why is Uranus blue-green?
Its atmosphere contains a small amount of methane gas. Methane soaks up the red part of sunlight and lets the blue and green light bounce back out into space, so from a distance the whole planet looks a pale blue-green.
Could you land on Uranus?
No. Uranus has no solid surface to stand on. Below its clouds of hydrogen and helium there is a hot, thick fluid of water, methane and ammonia, and the pressure would crush a spacecraft long before it reached the small rocky core.
Has anyone sent a spacecraft to Uranus?
Only one. Voyager 2 flew past on 24 January 1986, about 81,500 km above the clouds, and found ten new moons and two new rings. Scientists have recommended a Uranus orbiter as the next big planetary mission, but it has not launched yet.
Quick quiz
Three questions for space cadets. Nothing is recorded.
- How long does Uranus take to go once around the Sun?
- Which spacecraft is the only one to have visited Uranus?
- The moons of Uranus are named after characters from which writers?
Neptune
Saturn
Earth