5 November 2021

This week clear skies and thin cirrus clouds produced optical phenomena in the sky.

On 3 November the waning crescent moon rose just before sunrise, reminding me of the upside down rainbow I saw two days before.

On Monday afternoon the sky had a thin skim of icy cirrus clouds and contrails that did not obscure the sun but allowed its light to create arcs and sundogs. This was the first time I’ve ever seen an upside down rainbow, the rare circumzenithal arc.

When the sun is low, arcs curve away [from it]. The circumzenithal arc, one of the most colorful of the ice-crystal phenomena, is always seen high in the sky. Its curve is centered on the zenith, and it is seen only when the sun is within 18-26 of the horizon.

— National Audubon Society: Field Guide to North American Weather

Here are two photos of the arc at 4:22pm, 1 Nov 2021.

Twenty minutes later the arc was gone but sundogs appeared as bright spots to the left and right of the sun. In this photo from Schenley Park Golf Course, one sundog is accentuated by a contrail. Downtown Pittsburgh is in the distance.

Check out this amazing photo of a halo, two sundogs and a circumzenithal arc in Riedbergpass, Germany. I’d love to see this one day. Keep looking up!

(photos by Kate St. John)