It's not uncommon to see one ring around the Moon. But two? On Oct. 23rd, Martin Popek of Nýdek, Czech republic, photographed a rare pair:

Image
© Martin Popek
The outer 22 degree circumscribed halo is caused by moonlight shining through six-sided pencil-shaped ice crystals in the air. This is a familiar sight to backyard sky watchers. Less familiar is the 9 degree inner ring. It is caused by ice crystals with a strange pyramidal shape. The 9 degree ring is the innermost of many possible "odd-radius" halos caused by pyramidal ice crystals. Atmospheric optics expert Les Cowley notes that "pyramidal crystals [might not be as] rare as previously thought" and he urges sky watchers to "search carefully for their halos whenever the skies look favourable."

More images: from Denis Joye of Boulogne, France