Not quite a rainbow: What is a circumhorizontal arc?

(Courtesy: Suzie Harlan)

NASHVILLE, Tenn. (WKRN) – Something really cool happened Monday, and our viewers David Colin in Murfreesboro and Suzie Harlan in Nolensville captured the event on camera.

It looks like a rainbow, but it is actually called a circumhorizontal arc.

In order for these arcs to form, the sun must be high, up over 58 degrees above the horizon.

They are caused by sunlight entering horizontally into hexagonal ice crystals in cirrus clouds and exiting out at a 90 degree angle, which causes well-separated colors.

You will always see them appear with red at the top and indigo at the bottom.

(Courtesy: David Colin)