Saturday, October 11, 2008

210/365 Sun dogs and haloes

On my way home from work last night, I looked up at the setting sun and saw one of my favorite optical phenomena, sun dogs (though I couldn't remember what they were called), or what appeared to be small rainbows on horizontal opposites of the sun.

I captured some photos while I was still driving, in case they disappeared, but they remained for more than half an hour and were still visible when I stopped to pick up a couple pizzas.

I came home and looked it up in my National Audubon Society Field Guide to North American Weather (yep, I told you I was a nerd for meteorology!), and this is a combination of two phenomena -- sun dogs, or parhelia, and a 22-degree halo.

In this photo, you can see the sun dogs best on the left side, straight to the left of the sun. Then, if you trace it upward in a perfect halo around the sun, you can see the faint halo all the way around to the right side. When I first noticed this, the sun dogs were visible more on the right side.

According to my Field Guide, both haloes and sun dogs are caused by "refracted light passing through ice crystals in cirriform clouds that lie between the observer and the light source (in theory, haloes can be seen around any light source)." They're most often seen in the Southwest, where the climate is dry, but they can be seen anywhere and at any time of the year.

Isn't it cool?

Camera: Canon PowerShot SD1000 at about 6:00 p.m.

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