Netherlands Circumzenithal Arc
October 03, 2004
The above photo of an elegant circumzenithal arc was taken from Middelburg, Zld, in the Netherlands on August 28, 2004. Like all halo phenomema, circumzenithal arcs owe their color to refraction in hexagonal ice crystals, typically found in cirrus clouds. Circumzenithal arcs form when sunlight passes through the uppermost basal faces of oriented, hexagonal plate crystals and then exits through vertical side faces. The angle between these two faces is 90 degrees, which disperses the colors widely. Since there's little overlap between the colors, the hues are fairly pure, more so than those of a rainbow.