by Grietha Kroeze on 9th June '08 in The Netherlands.
©Grietha Kroeze, shown with permission.
The parhelic circle rings the sky always at the
same altitude as the sun.
It can be an elusive halo because it not coloured
and is sometimes difficult to distinguish from a cloudy background.
Halo colours are generated when the sun's rays are refracted on
enetering and leaving ice crystals. Red is refracted less than blue
and so the colours are dispersed, split. However, most rays forming the
parhelic circle enter and leave ice crystals at exactly the same angle
relative to the faces. There is no net dispersion and so no colours.