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What caused this unusual "fire rainbow"?

CBS News logo CBS News 6/11/2018 Caitlin O'kane
What is known as a "fire rainbow" was seen over the sky in Vermont on Sunday, puzzling many people who asked local media for an explanation.: trish.jpg © Trish Lanfear trish.jpg

An iridescent rainbow-colored cloud seemed to magically materialize in the sky above Vermont on Sunday. The colorful streaks across the blue sky puzzled some people who saw it near the New York-Vermont border.

It's a "fire rainbow," WCAX reports. The phenomenon has made headlines before, and it's technically called a "circumhorizontal arc," National Geographic explains.

A similar fire rainbow made headlines in San Francisco less than two months ago. The National Weather Service shared several photos of that fire rainbow and an explanation from meteorologist Roger Gass. 

Circumhorizontal arcs occur when the sun is situated high in the sky -- higher than 58 degrees above the horizon -- and its light is refracted by ice crystals suspended in the atmosphere, most commonly in cirrus clouds. "When the sun hits the ice crystals, you get pretty colors," Gass told SFGate.com. "It's an optical illusion."

A lot of you saw this phenomenon in the sky on Sunday. It is commonly called a "fire rainbow" because it looks like a...

Posted by WCAX-TV on Monday, June 11, 2018

Several people who spotted the colorful clouds overhead in Vermont on Sunday sent photos to WCAX, wondering what was causing the unusual sight. There were just a few wispy cirrus clouds in the bright blue sky, but that was enough to spark a fire rainbow.

A "Fire Rainbow" 🔥🌈 was captured over @PinnaclesNPS yesterday. The more scientific name is a circumhorizontal arc. For more details http://bit.ly/2qUuFCm #cawx #atmoshpericoptics 📸 M. Jimenez

Posted by US National Weather Service San Francisco Bay Area/Monterey California on Wednesday, April 25, 2018

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