Cloud iridescence is the occurrence of colors in a cloud similar to those seen in oil films on puddles, and is similar to irisation. It is a fairly uncommon phenomenon, most often observed in altocumulus, cirrocumulus, lenticular clouds and cirrus clouds. The colors are usually pastel, but can be very vivid. While they may look Photoshopped, all of these clouds that you’re about to see are just a naturally occurring phenomena. Continue reading for more interesting facts.
5. Generally Produced Near the Sun
Iridescence is generally produced near the sun, with the sun’s glare masking it, so it is more easily seen by hiding the sun behind a tree or building. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water.
4. Caused by Small Water Droplets
Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals produce halos.
3. Cloud Must be Optically Thin
If parts of clouds have small droplets or crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet.
2. Mostly Seen at Cloud Edges
Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence.
1. Sometimes May Form a Corona
When a thin cloud has droplets of similar size over a large extent, the iridescence takes on the structured form of a corona, a central bright disk around the sun or moon surrounded by one or more colored rings.