So-called "fire rainbows" are neither on fire nor are they rainbows, but they sure are stunning.
They are technically known as iridescent clouds, a relatively rare phenomenon caused by clouds of water droplets of nearly uniform size, according to a release by NASA. These clouds diffract, or bend, light in a similar manner, which separates out light into different wavelengths, or colors.
That makes them similar to rainbow-colored glories, which are also formed by diffraction, and also produce an oscillating pattern of colors ranging from blue to green to red to purple and back to blue again.
