Hale Pohaku Fogbows
September 06, 2007
Fogbows are rainbows that are formed in clouds or fog. In both cases, they're formed when sunlight is refracted and scattered by spherical water drops. Cloud droplets are 10-40 micrometers in diameter, much smaller than raindrops’ diameters of a millimeter or two. This makes the fogbow much broader and less colorful than the more familiar rainbow. Being optically identical to the rainbow except for particle size, a fogbow display contains the same elements: primary bow, secondary bow and supernumerary bows.
This picture was taken in June of 2005 at Hale Pohaku, the astronomer's village on Mauna Kea in Hawaii. The primary bow is prominent, but the other two are more subtle. The secondary rainbow can be faintly seen above the primary bow. Just below the primary bow is a supernumerary fogbow, best visible in the left hand part of the picture. A schematic diagram is shown below the photograph.