These are fire rainbows – the rarest of all naturally occurring atmospheric phenomena. The clouds needed for these rare events have to be cirrus and at least 20,000 feet in the air, with just the right amount of ice crystals. The sun also has to hit the clouds at precisely 58 degrees.
It looks like a rainbow on fire, but this phenomenon is as cold as ice. Known in the weather world as a circumhorizontal arc, this isn’t a rainbow in the traditional sense – it is caused by light passing through wispy, high-altitude cirrus clouds.
What’s more, the hexagonal ice crystals that make up cirrus clouds must be shaped like thick plates with their faces parallel to the ground for a fire rainbow to appear.
When light enters through a vertical side face of such an ice crystal and leaves from the bottom face, it refracts, or bends, in the same way that light passes through a prism. If a cirrus’s crystals are aligned just right, the whole cloud lights up in a spectrum of colors.
The phenomenon is quite rare because the ice crystals must be aligned horizontally to refract the high sun. The arc is formed as light rays enter the horizontally-oriented flat hexagonal crystals through a vertical side face and exit through the horizontal bottom face.
It is the 90 degrees inclination that produces the well-separated, rainbow-like colors and, if the crystal alignment is just right, makes the entire cirrus cloud shine like a flaming rainbow.
The absolute wonder of these spectacular events is that they can be very short-lived, rarely surviving beyond half an hour, simply because all of the factors involved must be just so before it can happen.
The series of pictures seen here was taken in the USA, where you are most likely to witness these events.
It is truly difficult to tear your eyes away from these spectactular images, and gratifying is the knowledge that this wondrous display comes absolutely free should you be lucky enough to ever see it. We live on a unique planet in the universe, and should be immensely grateful for the incredible diversity of natural experiences that surround us. Beauty is waiting for all of us in the great outdoors. All we need do is go there and open our eyes.