On Wednesday, while I was still at Boy Scout camp with my two older sons and their troop, we took a tour of the Bigelow observatories. It was a lot of fun, with about 60 kids attending. Since I have spent nights observing at the 61" Kuiper Telescope, I didn't get anything new out of it but it's always fun to visit the scopes again.
Around lunchtime on Thursday, someone looked up and soon we were all looking up. Although it was partly cloudy, a beautiful rainbow halo surrounded the sun. Unfortunately I didn't have my camera with me at the time, so I asked one of our scouts, Mitch, to snap a picture. Here's what he got. The camera didn't have a wide enough field but the rainbow did go the full 360 degrees. This picture does not show the full colors that were visible to the eye, it really was quite awesome.
This is what's known as a "22 degree halo", and it results from sunlight refracting off ice crystals in very high clouds. It's always the same diameter, because the ice crystals refract the light starting at about 21.7 degrees for the red; inside the ring, notice how the sky is darker - nothing is refracted in there. More about the science of these rings can be found at the Atmospheric Optics website.
All told it was a great camp week, but now I'm back down in the heat and monsoons.
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