Haloes in the winter sky. Historical artwork of a spectacular display of haloes around the Sun over a snowy forest. Haloes are formed by the refraction of the Sun's light inside tiny regular ice crystals in the atmosphere. The most common is a 22 degree halo around the Sun (inner circle), which often has two sundogs (or parhelia, white streaks) extending horizontally from its edge level with the Sun. Outside the 22 degree halo is a rarer 46 degree halo. At top is a circumzenithal arc. Those last two haloes are relatively rare, as the crystals that form them require very exact conditions in which to form. Artwork originally published in The Atmosphere by Camille Flammarion, in 1873.