What causes a 'moon halo' to appear in the night sky?

ASHEVILLE, N.C. (WLOS) — Did you see it? Several News 13 viewers shared images of a ring appearing around the moon Sunday night.

A "moon halo" or "moon dog" is an optical illusion created by the collision of light waves with ice crystals in Earth's atmosphere.

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It happens when light from the moon is refracted by tiny ice crystals found in a thin layer of cirrus clouds 15,000-30,000 feet above the surface of the Earth. These floating ice crystals effectively create a lens in the atmosphere creating arcs or a ring appearance around the moon.

Moon halos are more visible around a full moon during the colder, winter months, which happened this past weekend.

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February's full moon is known as the "Snow Moon," which is happening Friday night into early Saturday morning, Feb. 23-24.

The presence of high, thin clouds Sunday night, Feb. 18, were thanks to a passing, upper-level-low moving east across the southern U.S. By Monday morning, those clouds cleared the Western Carolinas to bring a sunny, blue sky to start the week.