When you think about cool natural phenomena involving light, your first thought is probably the northern lights. But there's another phenomenon that's more rare and just as impressive: light pillars. Light pillars occur when light that's close to the ground (reflected sunlight or street lamps, for example) bounces off ice crystals in the air. (National Geographic has a good explanatory diagram here.) They appear mainly in polar regions — but thanks to this year's frigid temperatures, they've been recorded much further south than usual, and much more often. If you were in Peterborough last night, for example, you might have seen them. They look like UFO beams or spotlights, only incredibly bright and often appearing in clusters. In the gallery above, we've collected a few stunning examples from the last couple of weeks.