What makes fire rainbows particularly special is the fact that they need very specific conditions to occur.
First, the sun must be higher than 58 degrees in the sky. Second, they require cirrus clouds—those wispy, thin clouds that are formed at higher altitudes where the air temperature is low enough to form the clouds from hexagonal (six sided) ice crystals. And third, these conditions need to be perfectly aligned for the ice crystals to act as a prism to create refractions and reflections from the sunlight, resulting in a horizontal “rainbow” display of color.
In spite of the exacting requirements, this iridescent halo effect is not as rare as one might think. Their frequency depends on the required conditions being in the right location in a particular latitude in the northern hemisphere during summer, notably in the months of June and July in the USA. They often appear on the horizon and beautiful examples have been captured above the clouds through aircraft windows.