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| Earth on Oct 16, 2012

What is a fogbow?

Fogbows are rainbow’s cousins, made in much the same process, but with fog instead of rain.

A fogbow is much like a rainbow, made from the same configuration of sunlight and moisture. That is, you see a fogbow in the direction opposite the sun. But fogbows are caused by the small droplets inside a fog or cloud rather than the larger raindrops that caused rainbows. 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 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.

Katherine Keyes Millet captured this fogbow in July 2014 at Winter Island park in Salem, Massachusetts.

View larger. | Katherine Keyes Millet captured this fogbow in July 2014 at Winter Island park in Salem, Massachusetts.

Fogbow seen over Sunset Cliffs in San Diego on October 15, 2012 by EarthSky Facebook friend Jim Grant. Thank you, Jim. Click here to expand image

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 …

fogbow-August-24-Salamapaja

A fogbow seen in Finland, captured by Thomas Kast. You can see more of his photos here.

Thomas Kast captured the beautiful fogbow above and had this to say:

Last night – August 24/25, 2013 – I was hoping for a great aurora show due to the expected CME. No auroras, but mother nature gave me treat I’ve never seen before!

In this rather cold August night (+8C) there was patchy fog, especially in open fields. This lake remained clear for a long time. At one point I saw this white bow with moon in waning gibbous phase behind me …

EarthSky Facebook friend Lynton Brown of Australia captured this fogbow. See more photos from Lynton Brown here. Click here to expand image

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.

Look here for Les Cowley’s explanation of how fogbows form.

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.