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What is a fogbow?

Fogbows are rainbows’ cousins – made in much the same process – but with the small water droplets inside a fog instead of larger raindrops.

GregDiesel Landscape Photography wrote on October 22, 2015:

GregDiesel Landscape Photography wrote on October 22, 2015: “Saw my first fogbow / white rainbow. Photo taken with cell phone. Moyock, North Carolina.”

Fogbows – sometimes called white rainbows, cloudbows or ghost rainbows – are made much as rainbows are, from the same configuration of sunlight and moisture. Rainbows happen when the air is filled with raindrops, and 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.

Venus and Jupiter above a fogbow in Blacklough, Dungannon, Ireland.  Mars is up there, too, but tough to see.  John Fagan captured them all on October 27, 2015.  Thank you, John!

Venus and Jupiter above a fogbow in Blacklough, Dungannon, Ireland. Mars is up there, too, but tough to see. John Fagan captured them all on October 27, 2015. Thank you, John!

Eileen Claffey in Massachusetts captured this fogbow over a field in 2014.

Eileen Claffey in Brookline, Massachusetts captured this fogbow over a field in 2014.

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

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

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.

fogbow-August-24-Salamapaja

A fogbow seen in Finland in 2013, captured by Thomas Kast. He wrote: “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.” See more photos by Thomas Kast.

View larger. | Fogbow seen over Sunset Cliffs in San Diego on October 15, 2012 by EarthSky Facebook friend Jim Grant.  Thank you, Jim.

View larger. | Fogbow seen in 2012 over Sunset Cliffs in San Diego by EarthSky Facebook friend Jim Grant. He wrote: “The skies were sunny and clear, and then the fog rolled in, and with it this beautiful fogbow.” Thank you, Jim.

View larger. | EarthSky Facebook friend Lynton Brown of Australia captured this fogbow over a barren field, in autumn, in 2012. See more photos by Lynton Brown.

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.

Deborah Byrd

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