circumhorizontal arc is an optical phenomenon - an ice-halo formed by plate-shaped ice crystals in high level cirrus clouds - other currently accepted names are circumhorizon arc or lower symmetric 46° plate arc - the term "fire rainbow" is misleading as it is not a rainbow
This is a rare meteorological phenomenon called a skypunch. When people see these, they think it's the end of the world. Ice crystals form above the high-altitude cirro-cumulo-stratus clouds, then fall downward, punching a hole in the cloud cover.
"Not every cloud has a silver lining; this multi-coloured cloud looks as if a rainbow has formed high in the heavens. The phenomenon – called a sundog – happens when ice crystals appear in clouds and refract the sun’s rays. Photographer Robert Arn captured the cloud in Heyworth, Illinois, America."