Uranus experiences a 21-year-long dark winter due to its extreme axial tilt. Uranus rotates on its side, with its rotational axis inclined about 98 degrees relative to its orbit around the Sun. During Uranus’ 84-year orbit around the Sun, each pole points toward or away from the Sun for approximately 21 years. This causes one pole to have a 21-year-long gloomy winter, while the other pole has a 21-year-long summer with constant daylight.