Suppose you are standing at the North Pole of Uranus, by the way, you can’t you would sink right in, But if you could you would see the Sun appear on the horizon circle higher and higher for 21 years. Then circle back down to the horizon over the course of another 21 years. Once the Sun went below the horizon, you would experience another 42 years of darkness before the Sun appeared again now that’s a long wait. But why does this happen?
It all started with something huge that smashed Uranus some 1 billion years ago and locked it over on its side. While the other planets looked like spinning tops as they revolve around the Sun Uranus is flipped on its side and appears to be rolling around the Sun. This has a weird and dramatic effect on the seasons on Uranus.
Uranus like Earth has four seasons, however, the seasons on earth and Uranus are very different. It takes Earth 365 days to orbit around the Sun, but it takes Uranus the equivalent of 84 years here on earth. So 1 Uranus year is 84 earth years long and each season on Uranus lasts 21 earthly years. But it’s the tilt of the planet that makes this season weird.
It’s unusual seasons just as Earth’s seasons are caused by planet’s own tilt on its axis, but the tilt of our planet is very different. Earth’s axis is tilted 23.5 degrees from the plane of its orbit around the Sun whereas with respect to its orbit the axis of Uranus is tilted at an angle of 98 degrees.
During the summer earth has a Midnight Sun at its poles and a long polar night in winter, but those dark and bright times at Earth’s poles only affect a smaller part of our planet and don’t last nearly as long as they do on Uranus. During Uranus’s winter/summer season the winter side of the planet doesn’t see the Sun at all for 21 long years. Meanwhile, the summer side of the planet has continuous daylight.
However, during its spring and fall seasons, Uranus is oriented in its orbit so that sunlight strikes its equatorial region, which drastically affects the lengths of its days. Uranus spins on its axis about every 17 hours and 14 minutes making that the length of its day and night. Day and night cycle so for much of the planet where there had once been a continuous day or continuous night lasting decades on an earthly scale. Now there is a relatively rapid change between day and night all depending solely on the seasons.