Halo

• a ring of light encircling and extending outward from the sun or moon
• created as sunlight is refracted as it passes through ice crystals.
• indicates cirriform clouds (high, thin clouds composed of ice crystals)
• two types:
  • 22° halo - refraction of light through randomly falling ice crystals.
  • 46° halo - refraction of light through hexagonal column-type ice crystals.
• here is a 22° and 46° halo

photo by N. Atkins