Sun dogs, also known as parhelia, are bright spots that appear on either side of the sun, typically when it is low on the horizon. They occur due to the refraction of sunlight through ice crystals in the atmosphere, often found in cirrus or cirrostratus clouds. These optical phenomena can create a halo effect around the sun, making it look like there are additional suns nearby. Sun dogs are most commonly seen in cold climates, where ice crystals are more prevalent, but they can occur anywhere under the right atmospheric conditions.