Transcript: Uranus has two very unusual aspects to its orbit. The first is the large degree of tilt of the spin axis with respect to the plane of its orbit around the sun. This tilt is ninety-eight degrees, so the pole of Uranus is essentially in the plane of its orbit around the Sun. This is more extreme even then the tilt of the Earth's axis which is only twenty-three and a half degrees. As a result, in its 84 year orbit of the Sun, Uranus experiences extremely long seasons because for 20 or 30 years at a time, when the north pole is pointing directly away from the Sun, the northern hemisphere of the planet is in deep winter, exacerbated by its large distance from the Sun as well. These long and extreme seasons are unique among the planets. In common with only Venus in the solar system, Uranus has a retrograde orbit that is unlike the Earth and the other planets which prograde orbit, that is, they rotate from west to east, and so the spin of the planet is in the same sense as its orbit of the Sun. Uranus is the reverse. Astronomers speculate that the reason for Uranus' strange orbit, as with the Earth, is a collision early in its history. Perhaps a glancing blow left Uranus with a highly tilted orbit.