A rare and colorful sight was spotted in the South Carolina sky last Sunday. Dozens of beachgoers photographed what many referred to as a "fire rainbow" above the Isle of Palms outside Charleston. Unfortunately, the term used to describe this display is incredibly inaccurate. This so-called "fire rainbow" isn't a rainbow at all; it's actually a circumhorizontal arc.
Rainbows are formed when beams of sunlight hit a raindrop and separate into various colors. A circumhorizontal arc, on the other hand, happens when light passes through clouds at a high-altitude. The light is refracted through the cloud's ice crystals and forms a bright color spectrum.
So even though the most glaring issue with the name is the use of the word "fire" — fires have nothing to do with this — the biggest problem is that there was no rain involved in the formation of Sunday's circumhorizontal arc.
The term is a "complete misnomer, akin to identifying a conventional gasoline engine as an electric motor," says Raymond Lee, a meteorologist at the US Naval Academy. That said, given the ongoing drought in California, it's pretty refreshing to see such positive coverage of a weather event in the US. But just make sure you call this colorful phenomenon by its proper name.