Why does the moon sometimes have a 'halo'?

Rings can appear around the moon because of ice crystals high in the atmosphere. (Image credit: J.P.Andersen Images/Getty Images)

If you've ever looked up at the full moon in the night sky, you may have noticed a large halo of light around it. But why does this lustrous ring sometimes encircle our natural satellite?

While it might seem like a sign you need a new glasses prescription, it's really caused by ice crystals high up in the atmosphere.