The sky held a fire rainbow over the New River foothills North of Phoenix today. It lasted for about half an hour. I was at 5 Acre Arts, Lynda was giving me a ride in her ATV through some pretty uncharted terrain when I saw it. I didn’t think it would show up on my iPhone camera, but it did, and quite nicely, too.
Fire rainbow in New Rivier, AZ (c) Quinn McDonald, 2009
Technically, it is not called a fire rainbow, as it has nothing to do with fire and isn’t really a rainbow, it’s a halo. I like the name, though, so I’m going to be less precise and call it that.
Victoria Gilman, a writer for National Geographic, explained the phenomenon in a 2006 article:
It looks like a rainbow that’s been set on fire, but this phenomenon is as cold as ice.
Known in the weather world as a circumhorizontal arc, this rare sight . . .isn’t a rainbow in the traditional sense—it is caused by light passing through wispy, high-altitude cirrus clouds. The sight occurs only when the sun is very high in the sky (more than 58° above the horizon). 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.
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.
You can see the cirrus clouds in the photo–those thin row-like clouds. They carry ice crystals and generally signify a change in weather.
Circumhorizontal arc, 16 April, 2009 (c) Q. McDonald
These halos are rare, and not visible north of 55 degrees N (Northern Europe) or South of 55 degrees South (the Southern end of South America). I could have easily been inside, or not paying attention. It was a gift, and one I’m profoundly grateful for.
—Quinn McDonald is a writer and creativity coach. She teaches people who can’t draw about raw art journals.
QuinnCreative 
Thanks for explaining the phenomenon. Based on that, I would say that it is indeed a rainbow. Rainbows happen when light is refracted through water droplets, and since they are more or less spherical, rainbow happen fairly easily. Fire rainbows depend on ice plates lying all arranged properly and the sun has to be above them.
A rainbow is also a halo, a part of a circle, and depending on where you are, it can be more or less complete. I have had the good fortune of seeing a fire rainbow just once in Switzerland, and it wasn’t nearly as clear or as pretty. But I also felt fortunate for being in the right place at the right time, and looking.
I wasn’t sure why there was such a kerfluffle (in the research I did to find out what it was) that it wasn’t a rainbow. The only difference I saw was that the water was frozen, and it was a trickier arrangement, with more restrictions. Still a rainbow. But I did enjoy it!
Lovely–a fire rainbow. What a gorgeous thing to see.
It was beautiful and lasted longer than I thought–about half an hour.