Thursday, December 18, 2008

Winter Solstice

At noon on Dec 18, 2008, I measured the length of the shadow cast by a 12.125 inch ruler. It was 28 inches.
arctan(12.125/28.0) = 23.41˚.

That means the sun is 23.41 degrees above the horizon. I live at 43˚ north. The earth is inclined 23.5˚. So if the north pole is pointed directly away from the sun, at midday I expect the sun to be 90 – (43 + 23.5) = 23.5 degrees above the horizon. Noon isn’t precisely midday, so it was a smidgen lower. If the weather is cloudy for the next few days, I might not see the sun this low in the sky till next year.

This is how the winter holidays got started, and I think it’s a good reason to eat some treats and stop to remember the big picture.

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