Weatherz School: Sundogs, halos and pillars

When the right conditions come into place, the atmosphere can provide us with stunning visual effects. In order to understand the cause of what we’re seeing, let’s establish the difference between refracted light and reflected light.

When light is refracted inside an ice crystal or water droplet, it’s broken into its components, giving us all the colors of a rainbow. When light is reflected, all wavelengths are being reflected at equal angles, so we don’t get the full spectrum of colors.

Sundogs are a product of refraction. Sunlight is refracted by hexagonal-shaped ice crystals. The light is bent 22 degrees as it passes through the ice crystal and reaches our eyes. The bending of the light results in an optical illusion known as a sundog located about 22 degrees on the left or right of the sun.

Halos are also a product of refraction. A halo is a ring that forms around the sun or moon. The light refracts off ice crystals within a thin layer of clouds.

Sun pillars are shafts of light extending from the sun. These are caused by sunlight reflecting off of ice crystals. They form when the sun is low on the horizon, near sunrise or sunset.

In the case of ice pillars, you don’t need the sun. When it’s cold enough for ice crystals to hang low in the atmosphere, pillars form over city lights. Since light is reflected, the light we see is the same color as the source of the light.