The circumhorizon arc or 'rainbow clouds. This amazingly beautiful natural phenomenon can be observed when the sun rises high in the sky. The rays of the sun when it passes through high-altitude clouds composed of ice crystals in the form of hexagons. The sunlight is refracted in these crystals in bizarre way, and as a result, we see “fire rainbow”. This phenomenon is not local, it can extend over several hundred square miles
Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be 20,000 feet in the air with the precise amount of ice crystals, and the sun must hit the clouds at 58 degrees.