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Parhelic Circle imaged 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.