My Twitter feed exploded on June 25 with reports of colorful, crazy-looking clouds, sundogs, Sun halos and more. The above image from Nathanial Burton-Bradford is just an example of the type of atmospheric effect called a circumhorizontal arc. These are sometimes referred to as “fire rainbows” but of course are not rainbows, and fire plays no role.
This is an optical phenomenon from sunlight hitting ice crystals in high cirrus clouds. It is actually a rather rare occurrence, but it happens most often during the daytime in summer when the Sun is high in the sky. This creates a rainbow-type effect directly in the ice crystal-filled clouds.
See more examples below.
You can find out more about circumhorizontal arcs from this article from Amusing Planet.