Circumhorizonal arc, Seattle area, Sunday 25 June 2017, 1:30pm local time:
(that light dot at bottom of the right photo is just a camera artifact that appeared whenever I tried to include the bright Sun in the photograph)
What I also found interesting about this arc was that apparently it's typically seen along with a 22.1° halo around the Sun as well, but ours didn't have the 22.1° halo. (See for example the picture below copied from the Wikipedia page on circumhorizonal arcs.)
There are all sorts of these types of features that can show up in the sky given the right conditions, with neat geometric derivations (for example one of my favorite Walter Lewin physics lectures is the one where he really clearly derives the 42° geometry for rainbows).
|(from Atmospheric Transmission, Emission and Scattering, edited by Thomas G. Kyle)|
A handful neat webpages that I've seen about these circumhorizonal arcs are:
- the Wikipedia page on circumhorizonal arcs
- the Wikipedia page on circumzenithal arcs
- a nice page about both 22 halos and circumhorizonal arcs
- and the circumhorizonal arcs page on the beautiful Atmospheric Optics website, which shows great photos of all sorts of different sky features like these.