© Kerri Trusz
The rainbow cirrus cloud also known as "feather clouds" or "mares tails" really looks like a feather floating in the evening sky.
Cloud iridescence is the occurrence of colors in a cloud. It is a fairly
uncommon phenomenon, most often observed in altocumulus, cirrocumulus, lenticular clouds and cirrus clouds.
Iridescence is generally produced near the sun. Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals produce halos.
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. Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, and newly forming clouds produce the brightest and most colorful iridescence.
© Terry Trusz