22-degree halo appears around the sun | TheUnion.com

22-degree halo appears around the sun

Residents of the Sierra foothills who happened to look briefly skyward Tuesday afternoon would have been treated to a spectacular celestial phenomenon.

A large rainbow halo surrounded the sun in a perfect circle for much of the afternoon.

The optical phenomenon, called a 22-degree halo, is created by millions of hexagonal ice crystals that form a thin layer of cirrus clouds in the upper layers of Earth’s atmosphere, said Drew Peterson, meteorologist with the National Weather Service.

“We had a deck of cirrus clouds as part of an upper-level system that came through central Northern California yesterday,” Peterson said.

“The size of the (Tuesday afternoon) halo was impressive. I’ve never seen one bigger …”

— Meteorologist Drew Peterson

The ice crystals act as a prism, which refracts the light rays a minimum of 22 degrees (actually 21.84 degrees), creating the brilliant halo, according to Georgia State University’s physics website.

“Those halos are not extremely common but not rare by any means,” Peterson said.

“The size of the (Tuesday afternoon) halo was impressive,” he said. “I’ve never seen one bigger, and talking to a lot of people in this building, it’s one of the biggest they had ever seen. That is part of what made it such a spectacular event.”

Rainbow halos also form around the moon and are often called a moon ring or a winter halo.

In folklore, the halos are said to warn of approaching storms, which is backed by science, as thin cirrus clouds often precede a large storm front.

National Weather Service meteorologists are predicting an unseasonably wet weather pattern delving into Northern California from the Pacific Northwest, slated to hit the region early next week.

“Record rainfall amounts are generally low this time of year, so some rainfall records may be threatened,” the National Weather Service states on its Facebook page.

Finally, the summer solstice will arrive a little early in 2013, as the sun’s rays will be directly over the Tropic of Cancer at 10:04 p.m. on June 20, according to the National Weather Service.

Solstices occur twice a year — once when the sun reaches its highest point in the sky (summer) and once when the sun is at its lowest point in the sky (winter).

To contact Staff Writer Matthew Renda, email mrenda@theunion.com or 530-477-4239.

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