Sun-dogs, February 1989.
Sun-dogs or parhelia (from the Greek “beside the sun”) are the two bright patches of light that are occasionally seen to flank the rising or setting sun. Parhelia are characteristically located 22° either side of and at the same elevation as the sun. They are produced by the refraction of sunlight through hexagonal-shaped ice crystals. Such ice crystals typically form in cirrus clouds at heights of between 5 and 10 km or, in very cold weather, they can form in ice clouds situated close to the ground. The hexagonal ice crystals that produce parhelia are typically a few tenths of a millimetre across, and are either plate or column-like in profile. Sun-dogs are formed when plate ice crystals are orientated with their hexagonal faces parallel to the ground. Randomly orientated column ice crystals will produce a circular halo with a radius of 22° about the sun. Reflection of sunlight from the upper and lower faces of near-horizontally orientated plate ice crystals can produce sun pillars (vertical columns of light extending above and below the sun). Sun-dogs are often seen in Saskatchewan skies on bright cold days. Moon-dogs (paraselenae) can also be produced by the refraction of moonlight through hexagonal plate ice crystals.
Martin Beech