The dog days of winter February 20, 2013
Posted by mareserinitatis in photography, physics.Tags: cold, pictures, refraction, sun dogs, weather
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A lot of people ask me how I can stand the winters here. Specifically, they just can’t imagine the cold during the winter. I mean, there can be no up side to -10°F and 30 mph winds. Also, those crazy Dakotans don’t seem to use MKS units. (Psychologically, it’s far worse to think about -23°C with 50 kph winds. Yeah, I know they’re the same, but this is why we keep using English units…)
Anyway, you’re wrong: there is an up side. Specifically, during the months of December to February, we get to see a lot of sun dogs around here. Sun dogs are refraction of sunlight by preferentially oriented ice crystals in the atmosphere. (For more info, you can always check the wiki article.) Sometimes, the refraction is really nice and they look like rainbows. Most of the time, however, it looks like there are two ‘mini suns’ on either side of the sun. They can be very bright.
I remember one particular instance where I had an office mate from India. I just left the office and saw some particularly good sun dogs, so I called her up and told her to go out to the west side of the building and check it out.
“I know what those are!” she said. “Those are rainbows! I’ve seen those before.”
“Yes, but have you ever seen them made with ice crystals?” She was a bit more intrigued then.
Even better, but more rare, are halos. These happen when the ice crystals are randomly oriented…such as when you have 30 mph winds. Yesterday morning, I got to see one such halo as I got to work. And because it was so cool, I had to share it with all of you.
Admittedly, it’s not the best landscape shot I’ve ever taken. However, I was in a hurry to get inside. It was freakin’ cold out there.
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Nice shot.