Moonbow Illuminates Evening Sky

moonbow strong and stanley
Jonathan Strong/Morgan G. Stanite

Last night we had many reports of a colored halo surrounding the moon.

What were we seeing?  News4 Meteorologist Tom Kierein says moonbows occur when light reflected off the moon causes a halo, similar to a rainbow.

But in moonbows, light reflected off of the moon is refracted by ice crystals contained by cirrus clouds high in the sky.  In the case of rainbows, the light is refracted through raindrops.

Both rain drops and ice crystals act as a prism to create a rainbow effect.  The size of the ice crystals determine how wide the moonbow bows.

The night sky requires two conditions for moonbows to show: the presence of high-atmosphere cirrus clouds, which are made of ice crystals, and a full moon.  The event is not common, but Tom Kierein says it's not especially rare, either.

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