In 1781, Uranus was the first planet to be "discovered" - all of the other planets had been observed from Earth since ancient times. It is a dull blue colour, mainly consisting of gas with a possible rocky core. Uranus has a faint ring system and at least 27 moons orbiting it. The planet is unusual because it orbits the Sun on its side, possibly the result of a collision during the formation of the Solar System.