fogbows

A fogbow, also called a white rainbow, is a pale arc or band that appears in fog or dense mist when sunlight or moonlight passes through tiny water droplets. Unlike a typical rainbow, a fogbow is faint and often nearly colorless, giving it a white or pastel appearance.

The formation of a fogbow is similar to that of a rainbow, but the droplets involved are much smaller. When light enters and is refracted, internally reflected, and refracted again by these tiny droplets, the dispersion of colors is greatly reduced. The resulting arc is broad and has very little color separation, usually with a slight red or pink tint at the outer edge in some conditions. The effect is most pronounced when the sun is low and the observer is within fog or mist.

Fogbows are commonly observed in fog banks, near coastlines, or around other sources of fine mist, when the sun is behind the observer and light passes through the fog before reaching the viewer. They can occur at night with moonlight, in which case they are sometimes called moonbows, although a fog bow in moonlight is often even fainter.

Observational notes: fogbows are best seen against a darker sky and are easier to spot when the fog is dense enough to produce a large number of tiny droplets, yet not so dense as to obscure the light entirely. They are a distinct phenomenon from rainbows, halos, and glories, though they can appear in the same weather conditions.