A few weeks ago we had a beautiful show of optical effects; we saw everything from sun dogs to halos around the sun. Matt Miller wrote a great blog labeling the different optical effects here.

Last night we saw something similar, a halo around the moon. Here are a few viewer submitted pictures of the halo.

The picture above was submitted by Pete Haack

The picture above was submitted by Scott May

A halo around the moon forms in the same way a halo around the sun forms. Light is refracted (or bent) by ice crystals, making a 22 degree halo. A 22 degree halo is the most common. See the diagram below to better understand how the light is refracted and where the 22 degree angle comes from.

Weather folklore says that a halo around the sun or moon means bad weather is on the way. I’ve also heard the number of stars inside the halo indicates the number of days before the bad weather will arrive.