Sky watchers often report seeing rainbow colors in clouds. There are various kinds of halos and colored arcs and even true rainbows you might see associated with clouds, but – if the rainbow-like colors are randomly distributed, and if the sun is nearby – what you’re seeing is likely an iridescent cloud.
These sorts of clouds are caused by especially tiny ice crystals or water droplets in the air. Larger ice crystals produce lunar or solar halos, but tiny ice crystals or water droplets cause light to be diffracted – spread out – creating this rainbow-like effect in the clouds.
The images on this page are mostly via the EarthSky community. Our thanks to all who contributed!
By the way, it’s easy to confuse circumhorizon arcs with iridescent clouds. Here’s how to tell the difference.
Bottom line: You might on occasion see a rainbow-like cloud. They’re fairly rare, but people do spot them, and we sometimes receive photos of them. They’re caused by the presence of very tiny ice crystals or water droplets in the air, which cause light to be diffracted (spread out).
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.