Image: Walter Tape
Colourful light pillars often appear in winter when snow or ice crystals reflect light from a strong source like the sun or moon. Aided by extreme cold, light pillars appear when light bounces off the surface of flat ice crystals floating relatively close to the ground. The pillars look like feathers of light that extend vertically either above or below the light source, or both.
Diagrams showing the formation of light pillars from street lamps (left) and the reflection of light rays from plate ice crystal surfaces (right):
Images: Keith C. Heidorn
Light pillars also form from strong artificial light sources like street lamps, car headlights or the strong light sources of an ice-skating rink as in the picture above of Fairbanks, Alaska. Though they are local phenomena, light pillars can look distant like an aurora. The closer an observer is to the source of the light pillar, the larger it seems.
National Geographic has more pictures of recent light pillars in Idaho, California, Belgium, Latvia and Canada. You can also view another Environmental Graffiti article on more incredible light phenomena here.