Why is there a rainbow around the sun or moon?

Why is there a rainbow around the sun or moon?
Rainbow halo around the sun from Snohomish, Wash. on May 20, 2011. (Photo courtesy: Twitter user @wplate)
By: Scott Sistek, KOMONews.com Meteorologist

You've all seen rainbows on those days where it's raining and the sun's out at the same time. But what about those times when you see a rainbow-like halo around the sun or moon?

It's the same physics, really. The halos (or, sometimes known as "sundogs" around the sun) are usually seen when there are high cirrus clouds overhead.

Those clouds are made of tiny ice crystals, which will refract the sunlight much like a prism will and voila! You have a rainbow halo around the sun.

It works the same way with moonlight, and it's usually a sign that rain is on the way, as high clouds usually precede a storm front.


Sometimes the rainbow isn't in the form of a halo, but just colors that just streak across the clouds -- the ice crystals in that cloud were at just the correct angle from the sun to produce the prism effect shown here -- known as "iridescence" or "fire rainbows"





Have you seen these rainbow clouds? If you've got photos, I'd love to see them and add them to our photo gallery here. You can email them to me at scotts@komonews.com.

Get more information and see more photos of different sun halos in My weather blog, "Partly to Mostly Bloggin"

Follow Scott on Twitter @ScottSKOMO and/or on Facebook