From Sundog to Halo

(Obscure videogame title jokes are us.)

These showed up over Somerville on the afternoon of Saturday the 27th.

Solar halos

Solar halos

Note that you're not seeing a blurred sun here! I was standing just inside the shadow of a building, so the sun was blocked out.

Photo times are 3:41 pm and 3:44 pm, Eastern time, Oct 27 2012. (iPhone 4 camera, nothing special.)

Displays like these are caused by ice crystals in the atmosphere. (Since ice crystals have many flat facets, they can make complex patterns. Raindrops are all round, which is why rainbows are always simple circles.) Apparently this happened across the Northeast as Hurricane Sandy approached.

More commentary and photos from my neighborhood.

A post-hurricane display in Alabama, same underlying cause. (Photo by David Hathaway.) This is a wider-angle photo which shows all of the bits that I saw (and more clearly).

A friend pointed me at this site diagramming all the things that are going on. There was definitely a circumzenithal arc touching a supralateral -- those are the bright upcurved "rainbow" and the dimmer one touching it. Then there's the upper tangent arc (the birdwing shape). The dark curve touching the bottom of the birdwing is a 22-degree halo. People were talking about a Parry arc, which I think is the brighter upper edge of the birdwing, but I'm not positive.

There was also a parhelic circle, which I didn't try to photograph -- it was a colorless brighter band visible widely left and right of the sun. As in the photo on the linked page, I could see sundogs (rainbow fragments) at two points on the circle.

It was fantastic, and got even more so when I got inside and started figuring out what I'd seen. Thanks to @ywwg for yelling about it and getting me outside.

-- October 28, 2012

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