Fogbows are sometimes called white rainbows, or cloudbows or ghost rainbows. They’re made much as rainbows are, from the same configuration of sunlight and moisture. Rainbows happen when the air is filled with raindrops. You always see a rainbow in the direction opposite the sun. Fogbows are much the same, always opposite the sun, but fogbows are caused by the small droplets inside a fog or cloud rather than larger raindrops.
Look for fogbows in a thin fog when the sun is bright. You might see one when the sun breaks through a fog. Or watch for fogbows over the ocean.
Because the water droplets in fog are so small, fogbows have only weak colors or are colorless.
Look away from the sun and at an angle of 35-40 degrees from your shadow which marks the direction of the antisolar point [point directly opposite the sun]. Some fogbows have very low contrast so look for small brightenings in the misty background. Once caught, they are unmistakable.
The sun must be less than 30-40 degrees high unless you are on a hill or high up on a ship where the mist and fogbow can be viewed from above.
Fogbows are huge, almost as large as a rainbow and much, much broader.
Bottom line: Fogbows, or white rainbows, always appear opposite the sun. Watch for them in a thin fog, when the sun is bright. You might see one when the sun breaks through a fog. Or watch for fogbows over the ocean.
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.
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