Sun dogs
Two bright, often coloured spots either side of a low sun, at the same height as it.
WhenBest when the sun is low, in the two hours after sunrise or before sunsetWhereLeft and right of the sun, at the same height as it
Why it happens
Flat, plate-shaped ice crystals drift down with their faces horizontal. Light entering one side and leaving another is bent by about 22 degrees sideways, so bright patches appear left and right of the sun rather than all the way round.
How to see it
The spot nearest the sun is red, then yellow, fading to a white tail that points away from the sun. In very cold weather ice crystals floating near the ground, called diamond dust, make dazzling ones with tails you can walk towards.
Field note. Sun dogs and a 22° halo often appear together; the dogs sit just outside the ring when the sun is high.