Different planets take different amounts of time to orbit the sun, depending on how far away they are. Uranus is much further away from the sun than Earth is, and it takes 84.3 Earth years for Uranus to complete its orbit. Like the other planets, Uranus follows an elliptical path around the sun, which means it is closer to the sun at some times than at others. At its closest, Uranus is 2.75 billion km away from the sun, and at its furthest it is 3 billion km away.
Earth has a small ‘axial tilt’, which means that it orbits the sun on a slight lean. Uranus has a strange feature of its orbit that most of the other planets don’t have. While the axial tilt of Earth is 23.5 degrees, the axial tilt of Uranus is a whopping 99 degrees! This means that Uranus is orbiting the sun completely tilted over onto its side. This means that Uranus has ‘seasons’ that are extremely different from most of the other planets.
While the two hemispheres of Earth have four seasons with differing weather patterns and amounts of sunlight, Uranus has two main seasons: for half of the year, the north pole of Uranus is in darkness because it is pointed away from the sun. For the other half of the year, the north pole has sunlight (and the sun never goes down). Remember that Uranus’ ‘year’ is 84 years long - imagine having 42 years of your life spent in sunlight, and the other half in the dark!
The sideways tilt of Uranus also creates interesting weather and cloud patterns that astronomers are interested in studying. Keeping track of the clouds on Uranus is tricky, as Uranus is so far away. When using a telescope on the ground, Uranus looks like a fuzzy blob! This is partially because there is a hazy layer on top of Uranus’ atmosphere, which makes Uranus look a uniform blue-green colour, and hides all the cloud formations. Newer telescopes have allowed astronomers to see more detailed aspects of the planets and weather patterns, but it is still very difficult for the weather patterns of Uranus to be studied.
Another interesting feature about Uranus’ orbit is that it allows us to see Uranus’ rings in a very special way. Uranus’ rings weren’t discovered until 1977, because they are made out of material that is extremely dark. Half way through Uranus’ orbit (every 42 years), the angle between Uranus and Earth lines up in such a way so as to allow us to see Uranus’ rings edge-on from Earth.
Figure 1: This infrared image of the dark side of the rings was taken by the Keck Observatory in 2007. The rings are visible because the widely separated ring particles scatter sunlight from the sunlit side of the planet to the dark side. Image credit: Keck Observatory, NASA (public domain).
This makes the rings look like a bright line passing through Uranus. When astronomers viewed Uranus’ rings most recently in 2008, they also found some new outer rings that they hadn’t discovered before. As time goes by, scientists will find out more and more about amazing planets such as Uranus, even though they are so far away!