Moonbow

A moonbow also known as a lunar rainbow, lunar bow or white rainbow is a rainbow produced by light reflected off the surface of the moon rather than from direct sunlight. Moonbows are relatively faint, due to the smaller amount of light reflected from the surface of the moon. They are always in the opposite part of the sky from the moon.

The term Moonbow was coined by Nick Whelan who sighted one of the first documented Moonbows in Eastern Utah.

It is difficult for the human eye to discern colours in a moonbow because the light is usually too faint to excite the cone color receptors in human eyes. As a result, they often appear to be white. However, the colours in a moonbow do appear in long exposure photographs.

Moonbows are most easily viewed when the moon is near to full and when it is brightest. For other than those produced by waterfalls, the moon must be low in the sky (less than 42 degrees and preferably lower), the sky must be dark and there must be rain falling opposite the moon. This combination of requirements makes moonbows much rarer than rainbows produced by the sun.

Few places in the world frequently feature this phenomenon. Cumberland Falls, near Corbin, Kentucky, U.S.A. and Victoria Falls on the border between Zambia and Zimbabwe, Durham, North Carolina and Waimea on Hawaii's Kauai Island are widely known for moonbow occurrence.