by BD Mitchell
One hundred facts that are interesting but ultimately useless.
- natural phenomena / physics -
A parhelion, or "sun dog", is a natural phenomenon that appears as a spot or patch of light -- usually in pairs -- flanking either side of the sun. A type of ice halo, parhelia are caused by sunlight refracting through atmospheric ice crystals. The hexagonal crystals act as prisms, and only light refracted at specific angles is delivered to the human eye, hence the sun dogs' predictable positions.
A similar effect that occurs with moonlight is called a parselene, or "moondog".