A fogbow is much like a rainbow, made from the same configuration of sunlight and moisture, but caused by the small droplets inside a fog or cloud rather than larger raindrops. Just as with rainbows, fogbows are seen in the direction opposite the sun. Look for one in a thin fog, when the sun is bright. You might see one when the sun breaks through a fog. Or watch over the ocean. Because of the small size of water droplets in fog, a fogbow might have only very weak colors, or no color at all. Colorless fogbows are sometimes called white rainbows.
Jim Grant in San Diego posted the image above on our Facebook page on October 15, 2012. He wrote:
This fogbow formed at Sunset Cliffs today. The skies were sunny and clear then the fog rolled in, with it this beautiful fogbow …
Lynton Brown posted the image above in Southern Hemisphere autumn (Northern Hemisphere spring) of 2012. It’s a fogbow over a barren Australian field.
Les Cowley of the great website Atmospheric Optics says:
Look away from the sun and at an angle of 35-40° from your shadow which marks the direction of the antisolar point. 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° 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 are rainbow’s cousins, made in much the same process, but with the small water droplets inside a fog instead of larger raindrops. Because the water droplets in fog are so small, fogbows have only weak colors or are colorless.