Uranus
Stop 10 of 12 · Outer Solar System
Uranus
A pale blue-green giant that rolls around the Sun on its side.
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Explore Uranus — an ice giant with a sideways tilt, a quiet blue-green glow, and decades-long seasons.
Leela's book shows a planet that looks almost like a calm, pale blue-green ball — no stripes, no great storm, just a soft glow. Something looks odd about it, though. It is tipped over, rolling along its orbit like a ball being pushed sideways.
"Why is it lying down?" Leela giggles. "Is Uranus tired?"
Why is Uranus blue-green? And why is it rolling on its side?
For the color: think about a glass of water with a drop of greenish ink in it — what color does the light passing through become? For the tilt: imagine a spinning top that got bumped hard, long ago…
Uranus gets its blue-green color from methane in its atmosphere. Methane absorbs red light, so the sunlight bouncing off Uranus returns to us tinted blue-green.
And the tilt? Long ago, something — likely a massive collision — knocked Uranus over. It now spins almost on its side, so its poles take turns facing the Sun for years at a time.
Seasons That Last Decades
Because Uranus is tipped so far, its seasons are extreme — each one lasts about 21 Earth years. One pole faces the Sun for a long summer while the other endures a long, dark winter.
It is also the coldest planet atmosphere in the Solar System, dipping to about -224 °C — even colder than Neptune, which is farther from the Sun.
- Order from Sun
- Seventh of the eight planets
- Approximate diameter
- 50,724 km
- Known moons
- 28
- Year length
- 84 Earth years
Uranus was the first planet discovered with a telescope, by William Herschel in 1781 — all earlier planets were known to ancient sky-watchers.
A Quiet World with Rings
Uranus has a faint system of rings and a family of 28 known moons. Its moons are named after characters from Shakespeare and Alexander Pope's poetry — a literary touch that makes Uranus unique among the planets.
Uranus is an "ice giant", like its neighbor Neptune. Ice giants are made largely of water, methane, and ammonia ices above a small rocky core — different from the gas giants Jupiter and Saturn, which are mostly hydrogen and helium.
Uranus rolls on its side with decades-long seasons. How might life be different on a world without familiar day and night?
Quick Check
Why does Uranus appear blue-green?
Uranus is an ice giant tipped onto its side by an ancient collision. Its methane atmosphere paints it blue-green, and its seasons stretch on for decades.
Reflect
What You Discovered
- Uranus rolls around the Sun on its side
- Methane in its atmosphere makes it blue-green
- Its seasons last for decades
- It was the first planet found with a telescope