Residents of Isle of Palms, South Carolina, were surprised by what they saw in the sky this past Sunday. A so-called “fire rainbow,” a twisted and colorful cloud, appeared in the sky and lingered for about an hour. The technical term for these phenomena is circumhorizontal arcs, and they occur in high-level cirrus clouds which are made up of tiny ice crystals.
“To produce the rainbow colors the sun’s rays must enter the ice crystals at a precise angle to give the prism effect of the color spectrum,” said meteorologist Justin Lock, adding the sun must be at an altitude of at least 58 degrees above the horizon. “Again, it has to do with getting the precise angle.”