THE SIDEWAYS PLANET

All planets in the Solar System rotate on an axis. This axis runs through the centre of the planet from North to South, and is usually on a slight tilt (this gives planets like Earth and Mars their seasons). It is like putting a cocktail stick through a ball and spinning it round. Uranus is the only planet (as far as we know) which rotates on its side, as if the planet has fallen over. Scientists believe that this happened when a planet, about the same size as Earth, hit Uranus and knocked it over. It causes the planet to roll around the Sun in its orbit like a barrel, and its moons, instead of going from left to right around the planet in their orbits, to go over the top of it and under. If we could see the moons orbiting Uranus close-up, it would appear like the lights on a ferris wheel.

Uranus' tilt also causes a night on one of the poles to last for 21 Earth years, a quarter of the time it takes for the planet to orbit the Sun. The picture below shows Uranus' orbit around the Sun.

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