What is happening on the planet Uranus?

Since British astronomer William Herschel discovered the planet Uranus in 1781, scientists have realized that it represents a world unlike the other planets in the solar system. However, the true surprises were only revealed after the Voyager 2 spacecraft flew by it in 1986, remaining the only space mission to have visited the planet to date. Observations showed that Uranus does not rotate on its axis like the other planets; instead, it appears to roll on its side as it orbits the Sun, a configuration that gives it the most extreme seasons in the solar system and subjects its poles to continuous decades-long periods of daylight or darkness.

Uranus’s axial tilt is approximately 97.8 degrees, compared to Earth’s tilt of just 23.4 degrees—a difference that creates this unique phenomenon. Rather than spinning like a top, the planet seems to tumble around the Sun. Although Uranus completes a rotation on its axis in roughly 17 hours, the succession of day and night at its poles is not determined by its rotational speed, but by its slow orbit around the Sun, which takes 84 Earth years. As a result, each pole experiences about 42 years of continuous sunlight, followed by about 42 years of perpetual darkness, with the poles alternating roles as the planet continues its orbital journey.

Jacob Kegerreis of the Institute for Computational Cosmology at Durham University describes this phenomenon, stating: “Uranus rotates on its side, with its axis of rotation pointing in a direction that is nearly perpendicular to the rotation axes of all other planets in the solar system.” The Planetary Sciences Group at the University of Wisconsin–Madison’s Space Science and Engineering Center notes that Uranus has an orbital period of 84 years and an axial tilt of approximately 97 degrees, causing its poles to alternate between 42 years of sunlight and 42 years of darkness.