| The most common of the halos is the 22 degree halo, a colored ring around
the sun or the moon with a radius of 22 degrees. It is sometimes called
the small halo. It has a fairly sharp reddish inner edge and a diffuse
bluish outer region. The 22 degree halo is caused by refraction between
faces inclined at 60 degrees in randomly orientated crystals. Like in
all halos the light from it is polarized. The 22 degree halo is visible
very often, though we are far more likely to see just a section of it
than the entire ring. An observer might expect to see this halo once every
five days. |
