The hexagonal ice crystals floating around in the atmosphere act like prisms, refracting the sunlight and breaking it up into its component colors. The reason sun dogs are more common at sunrise or sunset is because this is when the sun is lower, allowing for the sunlight to pass through more of Earth’s atmosphere and its light to be refracted by the ice crystals in the atmosphere. Some of these ice crystals are flat, hexagonal plates that can refract the sunlight when the sun is lower on the horizon. Having a thin veil of cirrus clouds in the atmosphere can also cause sun dogs to be present since cirrus clouds are made of tiny ice crystals. On clear days with an Arctic area of high pressure overhead, these ice crystals can be slowly moving vertically down in the atmosphere thanks to the gradual sinking motion of air under regions of high pressure. So what is required for sun dogs to form? On a bitterly cold winter day, ice crystals can be suspended in the air (sometimes from blowing snow, other times just due to water vapor molecules in the atmosphere freezing into tiny ice crystals).
The light is not separated into its component colors because it is not being “bent” (or refracted). On the other hand, reflection occurs when the light encounters a surface or object that does not absorb the energy of the light and bounces the light away from the surface. This creates rainbows with water droplets and sun dogs and halos in the winter with ice crystals in the atmosphere. So, when light is refracted inside an ice crystal or water droplet in the air, it is broken into its component colors (like a prism). A great example of refraction is when you stick a pencil in a glass of water, the pencil appears to be bent due to the refraction of light within the water. This is most commonly observed when light passes from one medium to another at any angle other than 90° or 0°. Refraction is the change in direction of light due to a change in its speed. Let’s first remember the difference between refracted light and reflected light.
(KFYR) - Sun dogs are always a bright spot on a bitterly cold winter day.
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