Ice crystals in distant cirrus clouds are acting like little floating prisms, Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizontal arc lies parallel to the horizon. Image © Todd Sladoje
A circumhorizontal arc is an optical phenomenon – an ice-halo formed by plate-shaped ice crystals in high level cirrus clouds.
Other currently accepted names for the phenomenon are circumhorizon arc or lower symmetric 46° plate arc.The misleading term “fire rainbow” is sometimes used to describe these phenomena, although they are neither rainbows, nor related in any way to fire. The name comes from its appearance as a rainbow taking the shape of flames in the sky.
This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009.