parhelion

Parhelion is an atmospheric optical phenomenon that manifests as bright spots on either side of the Sun. It is commonly referred to as a sun dog and is usually observed in the presence of high-altitude ice-crystal clouds, such as cirrus or cirrostratus.

Parhelia form when sunlight enters hexagonal ice crystals in the air and is refracted by these crystals. The crystals are often oriented with their bases horizontal, which directs portions of the light outward at about 22 degrees from the Sun, creating two bright patches. Parhelia are part of the halo family of phenomena and may be accompanied by a 22-degree halo or the broader parhelic circle under suitable conditions.

Color patterns typically show a red inner edge toward the Sun and a blue outer edge, and the brightness can range from faint to vivid. They are more readily seen when the Sun is low on the horizon and when thin, high-altitude clouds are present, but they can occur at many latitudes worldwide. The term parhelion derives from Greek para meaning beside and helios meaning sun; the plural is parhelia, with parheliums sometimes used as an alternative.