Stunning rainbow cloud formation - Cloud iridescence

Stunning rainbow cloud formation

Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds.

Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, a different phenomenon.

Irisation is caused by very uniform water droplets diffracting light (within 10 degrees from the Sun) and by first order interference effect (beyond about 10 degrees from the Sun). It can extend up to 40 degrees from the Sun.

Rainbow, rainbow cloud, sky rainbow