Sky watchers often report seeing rainbow colors in clouds. There are many different kinds of rainbow features you might see associated with clouds, such as halos and colored arcs and even true rainbows. But – if the rainbow-like colors are randomly distributed, and if the sun is nearby in the sky – what you’re seeing is likely an iridescent cloud.
These sorts of clouds are caused by particularly 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!
Bottom line: You might someday see an iridescent cloud. These clouds have rainbow-like colors. They’re caused by 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. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. 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. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. 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.
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