Sun Dogs and Halos | Outside My Window

29 January 2025

Clear skies and thin icy clouds have made this a great week for sun dogs and 22 degree halos in the sky. I’ve seen both near sunset this week: Last Sunday at Schenley Park golf course and yesterday at Duck Hollow.

Sun dogs are bright rainbow spots to the left and right of the sun …

… commonly caused by the refraction and scattering of light from horizontally oriented plate-shaped hexagonal ice crystals either suspended in high and cold cirrus or cirrostratus clouds, or drifting in freezing moist air at low levels as diamond dust. The crystals act as prisms, bending the light rays passing through them with a minimum deflection of 22°.

— Wikipedia account: Sun dog

Sometimes you see only one.

Last Sunday two sun dogs were connected by a 22 degree halo, a faint rainbow caused by the same atmospheric conditions as sun dogs.

If you’re really lucky you’ll also see a circumzenithal arc, an upside down rainbow at the top of the halo. I was fortunate to see all three on 5 Nov 2022 at Yellow Creek State Park.

I haven’t seen all three this week … yet. The best time is during the hour before sunset.

p.s. A halo can also occur around the full moon.