Uranus was originally called "George's Star" (Georgium Sidus). The summer in Uranus is 42 years long. Uranus has the coldest planetary atmosphere in the Solar System, with a minimum temperature of -371.56 °F (−224 °C). Uranus' axis of rotation is tilted sideways, so its north and south poles lie where most other planets have their equators. 63 Earths can fit inside Uranus. Uranus is the third-largest planet in the Solar System. Uranus orbits the Sun at a distance of about 2.8 billion km (1.7 billion mi) and completes one orbit every 84 years. Uranus was the first planet discovered with a telescope. The wind speeds on Uranus can reach 560 mph (900 km/h). Uranus rotates sideways and "rolls" around the sun rather than "spinning" like the other planets. Neptune was mathematically predicted before it was directly observed, based on the orbit of Uranus. There's a moon named Cupid that orbits Uranus. The chemical element Uranium, discovered in 1789, was named after the newly discovered planet Uranus. Uranus' moons are named after characters from the works of Shakespeare and Alexander Pope. Uranus has only two seasons: Summer and Winter. Jupiter has 67 moons, Saturn has 62, Uranus 27, Neptune 14, Mars 2 and Earth just one. Our exploration of Uranus has been entirely through the Voyager 2 spacecraft in 1985 and 86, with no other visits currently planned. The surface gravities of Venus, Saturn, Uranus, and Neptune are all quite similar (within 15%) to Earth's. In Chinese, Japanese, Korean, and Vietnamese, Uranus is literally translated as the "sky king star.". Uranus is the only planet whose name is derived from a figure from Greek mythology, the Latinized version of the Greek god of the sky Ouranos.