A ring of illuminated ice crystals encircle an Alaskan moon

Our sun isn't the only object in the sky that can produce spectacular optical effects. Take this photograph taken by Sebastian Saarloos on a cold, starlit Alaskan night. This is what's called a "moondog" — a rainbow-like ring around the moon that's caused by the reflection of moonlight (which is reflected sunlight) from ice crystals in the upper atmosphere.

The slightly overexposed photograph shows misty mountains in the background, along with an icy halo that surrounds the moon. Interestingly, because all ice crystals tend to have the same hexagonal shape, the moon ring is always the same size; moondogs, also known as paraselanae, are typically seen at an angle of 22 degrees.

Photograph courtesy Sebastian Saarloos. It was taken on January 17, 2013 from Lower Miller Creek, Alaska, USA.

_{Via NASA.}