What are Those Colorful, Crazy Clouds in the Sky??

by Nancy Atkinson on June 27, 2014

Ethereal and stunning sundog-like forms in the clouds called circumhorizontal arcs over Oxford, England on June 25, 2014. Credit and copyright: Nathanial Burton-Bradford.

Ethereal and stunning sundog-like forms in the clouds called circumhorizontal arcs over Oxford, England on June 25, 2014. Credit and copyright: Nathanial Burton-Bradford.

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.

Wispy clouds and a circumhorizontal arc over Italy. Credit and copyright: Elisabetta Bonora.

Wispy clouds and a circumhorizontal arc over Italy. Credit and copyright: Elisabetta Bonora.

Circumhorizontal Arc over the UK on June 25, 2014. Credit and copyright: Sculptor Lil on Flickr.

Circumhorizontal Arc over the UK on June 25, 2014. Credit and copyright: Sculptor Lil on Flickr.

You can find out more about circumhorizontal arcs from this article from Amusing Planet.

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

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