Uranus is an ice giant that orbits the Sun tipped on its side, a pale blue-green world found by telescope rather than known since antiquity.
At a glance
| radius | 25,400 km (3.98 × Earth) |
|---|---|
| distance from the Sun | 19.2 AU (2.88 billion km) |
| sunlight takes | 2.66 hours |
| one orbit | 84.3 years |
| orbit eccentricity | 0.046 |
| reflects | 49% of the sunlight it gets |
Read off the piece’s own catalogue, the same values it draws with.
About Uranus
Uranus is an ice giant: beneath a hydrogen and helium atmosphere lies a deep layer of water, ammonia and methane under great pressure, around a rocky core. Methane in its upper atmosphere absorbs red light, which gives the planet its cool blue-green colour. Its axis is tipped so far over that it rolls round the Sun on its side, so each pole spends a long stretch of its orbit in continuous daylight and then in darkness.
William Herschel found it with a telescope, the planet that first widened the Solar System beyond the worlds known since ancient times. It has a set of narrow, dark rings and a family of moons named after characters from Shakespeare and Pope. Only one spacecraft has ever visited it, Voyager 2, which flew past and saw an almost featureless disc.
What tipped Uranus over is not known for certain; a giant collision early in its history is the usual explanation. It also gives off surprisingly little heat from inside, unlike the other giant planets.
What you see in the piece
Uranus is lit only by reflected sunlight, which is dim this far out, and its narrow rings are drawn around it, standing up on edge with the planet’s tilt. Under dark skies it is just at the limit of the eye from Earth; from another star it is invisible.
Measured or modelled
The giant impact that tilted Uranus is the favoured explanation but a model, not an observation; slower processes involving a former moon have also been proposed.
Questions
Why is Uranus tilted on its side?
Nobody knows for certain. The most common explanation is a collision with a large body early in the Solar System’s history that knocked its axis over.
How long is a year on Uranus?
Uranus takes 84.3 years to go round the Sun, so each of its poles spends many years in sunlight and then many years in darkness.