Sivesøyler

Sivesøyler is a term originating from Denmark that describes a specific type of natural phenomenon observed in winter. It refers to the visual effect of a vertical column of light or color that appears to rise from a light source on the ground, such as a streetlamp or a building's floodlights, into the sky. This optical illusion is created when light reflects off ice crystals suspended in the atmosphere.

These ice crystals, often in the form of small, flat, hexagonal plates, are typically found in very cold, clear, and calm air. As light from a ground-based source strikes these crystals, it is reflected downwards, creating the illusion of a pillar extending upwards. The color of the sivesøyle is usually the same as the light source, but atmospheric conditions can sometimes subtly alter its hue.

Sivesøyler are most commonly observed during freezing temperatures when there is little wind, allowing the ice crystals to remain suspended in the air in a relatively stable orientation. They are a type of atmospheric optical phenomenon, similar to sun dogs or halos, which are also caused by the interaction of light with ice crystals in the atmosphere. While not a rare occurrence in cold climates, they are particularly noticeable and striking when present. The term is not widely used outside of Denmark.