A stunning sight in the sky: The science behind what causes a halo around the sun🌅

Halos form from the refraction of the sun’s light

A partial 22° degree halo observed near the Woodlawn Lake area on Sunday, March 19. Photo sent in via KSAT Connect from Taylor Mcclelland. (KSAT)

Ever so often, under the right sky conditions, an impressive atmospheric phenomenon occurs around the sun.

Known as the 22° halo, the light ring appears to surround the sun when a deck of high clouds is present.

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Have you ever wondered what causes those halos to form? Well, those high clouds are made up of ice crystals that refract the light twice: once when the light enters the ice crystal, and another when the light exits the ice crystal. These refractions bend the light 22° from its original direction, creating that halo effect.

The most common type of high cloud that causes this phenomenon is called a cirrostratus cloud, but sometimes halos can be found through cirrus clouds, too.

Cirrostratus clouds are semi-transparent and typically cover a larger area of the sky when compared to regular cirrus clouds. The term cirrostratus comes from the Latin language where “cirrus” means lock of hair (referring to a cirrus cloud’s wispy nature) and “stratus” means flattened or spread out.

Depending on that cirrostratus deck (like the one in the photo above), sometimes only part of the halo may form.

So the next time you look up and see a halo effect around the sun, you’ll know why it’s there!

About the Author

Meteorologist Mia Montgomery joined the KSAT Weather Authority Team in September 2022. As a Floresville native, Mia grew up in the San Antonio area and always knew that she wanted to return home. She previously worked as a meteorologist at KBTX in Bryan-College Station and is a fourth-generation Aggie.

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