I've Seen Fire, and I've Seen Rainbow

The Fire Rainbow: An Astonishing and Rare Marvel of Nature

To name it properly, a fire rainbow is a circumhorizontal arc. It is also known as a circumhorizon arc but whichever you chose, scientists (and aficionados) call it a CHA. It is given its name because it looks as if a rainbow has spontaneously combusted as it made its way across the sky.

Contrast with the circumzenithal arc (upside-down rainbow)

Somewhere, Under the Rainbow

Pictured: Rare upside-down rainbow spotted in the UK

Rainbows are formed when sunlight is refracted in a raindrop.

But in a circumzenithal arc, the colours are in reverse order from a rainbow, with violet on the top and red at the bottom.

The arc usually vanishes quickly because the cirrus clouds containing the ice crystals shift their position.

Ice particles in high cirrus clouds occur all year round, but circumzenithal arcs are usually obscured by lower level clouds.

Circumzenithal arcs are so named as they go around the zenith – the point in the sky directly above the observer- rather than the sun.

(Pedantic man notes that rainbows actually refract the light twice)

More on circumzenithal arcs

h/t to Caroline