This week Thinking Color takes to the skies to observe a colorful phenomenon. You have seen a rainbow before, but have you ever witnessed cloud iridescence? Cloud iridescence is the color spectacle caused by diffraction of light through ice and water particles in the atmosphere.
This phenomenon is relatively common but not often easy to observe. Due to the relation of the sun's position to the clouds the colors are often pastel and not easy to view without using dark glasses to block the sun.
In order to see the spectacular colors we see here several factors must align. First the particles that the light is passing through must be small in size, otherwise the light is seen as a halo rather than iridescence. Secondly the clouds must be newly formed and therefore free of contaminants. Finally, the clouds must be optically thin in order for the light to pass through to a viewer.