Technically called a circumhorizontal arc, fire rainbows are caused by light passing through wispy, high-altitude cirrus clouds. ... Fire rainbows occur only when the sun is very high in the sky (more than 58° above the horizon).

Where is the circumhorizontal arc?

A circumhorizontal arc (previously known as the lower circumzenithal arc) is a near-horizon arc and extends parallel to the horizon. A circumhorizontal arc is as colourful and bright as a circumzenithal arc. The circumhorizontal arc occurs only when the elevation of the light source is more than 58°.

What is a horizontal rainbow called?

This type of rainbow is known as a circumhorizontal arc. The physics behind how these horizontal rainbows form is quite different than that of the typical rainbow. This optical phenomenon is brought on by the way in which light passes through suspended ice crystals in the atmosphere.