“Fire Rainbows” (Circumhorizontal Arcs) & Cloud Iridescence

These phenomenons are and can be uncommon (especially depending on your location) and bloody cool! Like moon and sun halos, they work basically the same way: clouds in the atmosphere have ice crystals and water droplets that cause diffraction and scatter the light when the sun is at just the right angle. Circumhorizontal Arcs (aka “Fire Rainbows”) are more common than Cloud Iridescence, as the sun must be high in the sky for fire rainbows, which produce these massive halos that usually you can’t fully see due to your location or scattered clouds. Cloud Iridescence is with smaller crystals “closer” to the sun and in certain thin clouds. With that, classification of all these different phenomenons depends on the size of the crystals, degree of the sun (or moon), location (etc), giving us an awesome variety of atmospheric optical phenomenons to witness!

Photo credits for the above photos: not on your nelly, Pandiyan, colinjcampbell, Jeff Kubina, and Sean Stayte.