Rainbows happen when sunlight reflects and refracts within water droplets in Earth’s atmosphere, resulting in a full-spectrum arc of light in the sky. However, rainbows aren’t unique to Earth and now we have proof: an image of a rainbow on the planet Venus, taken by the European Space Agency’s Venus Express Orbiter.
The rainbows on Venus are a bit different than terrestrial ones. Instead of being shaped like an arc, which is what we’re familiar with, the Venus rainbows are “glories,” which means that their shape is more like concentric circles, creating a halo effect with a bright circular center like a lens flare. You can only see glories when you’re between the Sun and the cloud particles reflecting light. They are often seen on Earth, from high up, whether from planes or the tops of mountains. A glory occurs when you have spherical liquid droplets in a cloud that are all the same size.
Astronomers believe Venus contains lots of droplets made of sulphuric acid. So the Venus Express Orbiter sat with the Sun behind it and took images of the planet’s clouds. These images revealed the glories, which appear to be about 43 miles above the surface of Venus and about 745 miles wide. However, these glories pose a new mystery about the planet: the brightness of each glory’s ring varies, which could be due to other elements being present in the droplets other than sulphuric acid. This could be the same material that has been previously seen with ultraviolet measurements as dark areas in Venus’ clouds. Astronomers believe this material, whatever it is, could act as a UV absorber in the planet’s atmosphere.