«Fire» Rainbow (rounded horizontal arc) - a relatively rare optical effect in the atmosphere, manifested in the appearance of a horizontal rainbow, localized on a background of light, highly placed cirrus oblakov.
Rare phenomenon because the ice crystals in cloud must be oriented horizontally to refract sunlight. Rays enter through the vertical side wall of the flat hexagonal crystal, pass therethrough and out of the lower horizontal side. This arrangement provides a spectral color separation, which, like the rainbow, "lit" feathery oblako.
See also: White rainbow - a surprising phenomenon. The sky is falling? NASA satellites have found a decrease of clouds around the world. Amazing bird "air show" in Scotland.