Uranus is the third largest planet and the seventh planet from the sun. Uranus is the only planet that rotates on its side. Other planets orbit the sun and rotate like spinning tops, but Uranus' orbit more closely resembles a rolling ball.
Uranus is the coldest planet in the solar system, but Neptune is farther away from the sun. The other large planets in the solar system give off more heat than they absorb from the sun, but Uranus doesn't. Something has caused the core of Uranus to cool, so it no longer radiates much heat.
Uranus is the second least-dense planet after Saturn. It is 14.5 times more massive than Earth. Because its density is so low, a person standing on the surface of Uranus would only experience about 89 percent of Earth's gravity.
Whereas most planets have been known since ancient times, Uranus was the first planet to be discovered in the modern age. It was first recorded in 1690. Astronomers initially thought it was a star, but Sir William Herschel recognized it as a planet. Although it can be seen with the unaided eye in the right conditions, no one saw it was a planet until Herschel.