Why is there a ring around the moon? Winter halo lights up San Francisco Bay Area skies

SAN FRANCISCO (KGO) -- Have you ever seen a halo-effect or ring around the moon?

Known as a moon ring, a winter halo, or a 22-degree halo, it's when "ice crystals suspended high above in thin wispy cirrus clouds refract the moon's light to form a perfect circle," Meteorologist Drew Tuma says.

Tuma adds that it's rather common, "more common than rainbows."

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Weather.gov says the halo around the sun or moon is usually seen as a bright white ring and can sometimes have color.

Tuma suggests that we often miss the moon halo because fewer people are outside a night.

"In folklore, moon rings are said to warn of approaching storms," Tuma tweeted.


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