Home   What's New    Rays & Shadows   Water Droplets   Rainbows   Ice Halos     Contents     Crystals     Frequent Halos       22° circular       Sundogs         Diamond Dust         Moon Dogs         Images       Tangent Arcs       Circumscribed       Pillars       Circumzenithal       Parhelic Circle     Infrequent Halos     Multiple Displays     Other Worlds     Observing Halos     HaloSim   High Atmosphere   Links & Resources   Search - Index   123456789012345678		Sundogs - parhelia - mock suns
		A 7° high sun flanked by bright parhelia. Sundogs (parhelia, mock suns) are, with the 22º halo, the most frequent of the halos. Look for them, especially when the sun is low, at each side and about 22° away. This is the same distance or more** than the common circular halo. Sundogs reveal that the clouds are hosting horizontal plate crystals. These plates drift slowly downwards like leaves with their large faces almost horizontal. Sundogs are formed when light passes through crystal side faces inclined at 60° to each other.   The rays, like those of the 22° halo, are deviated by up to 50° but those near to the minimum deviation condition of near** to 22° are the most numerous and they form the very bright sundog inner edges. Sundogs are often brightly coloured because the crystals refract each colour by a different amount.       In the simulation a parhelic circle and a sun pillar, also produced by plate crystals, are visible. Some poorly oriented crystals produced the 22° reference halo. Sundogs often curve upwards in photographs and simulations, this is a projection effect and they are always at the same altitude as the sun.    ** Unlike the 22° circular halo, sundogs are not always 22° from the sun.   As the sun gets higher they pull away from the 22° halo because the rays forming them become increasingly skewed relative to the crystal axis. Take a look at Tom Eklund's image when the sun was 43º high.