Uranus was discovered by accident in 1781 by William Herschel, while at his home in Bath. It had been seen many times before but always dismissed as a star. Like the other gas giants , it is mostly atmosphere, with a rocky core that occupies a small fraction of the total diameter. The atmosphere is largely made up of hydrogen (83%) and helium (15%).
Its radius is approximately four times that of the Earth, making it the third largest planet in the Solar System. A day on Uranus lasts 17 hours, and it takes 84 years to orbit the Sun. It is an icy planet, shrouded by clouds that are coloured blue by the methane in its atmosphere.
