A parhelion, commonly known as a "sun dog," is an optical phenomenon that appears as bright spots on either side of the sun. It occurs when sunlight is refracted through ice crystals in the atmosphere, typically found in cirrus or cirrostratus clouds. This refraction creates a halo effect, often resulting in a bright, colorful display. Parhelions are most visible when the sun is low in the sky, such as during sunrise or sunset. They can occur anywhere in the world but are more common in polar regions. The phenomenon is related to other atmospheric optics, including halos and light pillars.