Friday, March 19, 2010

A sundial at work

I'm still in sundial mode. I recently completed an adjustable equatorial. Now that we are approaching the vernal equinox, the sun actually stays up for a reasonable time; it comes through my south-facing kitchen window at about 12 noon on that monstrous contrivance called "Daylight Savings Time," which saves no daylight, much less energy. However everyone is convinced that it does (save energy). They must have been watching TV. I have no TV, thus allowing me to make more sundials. Pardon the rant. Anyway, here is the equatorial sundial doing its thing:
The sundial is set -- as best I can by protractor -- to my latitude, 61deg 47m. Or sixty-two deg. give or take. The post in the center is called a stylus; or style; sometimes a gnomon. It is also the polar axis -- which is parallel to the earth's axis of rotation -- and the shadow gives the solar time. [I am actually lying over the polar axis bit. This is a sundial, not a telescope. But I don't want to complicate matters just now.] Not the zone time; although I suppose you could rotate the dial to give you AKST or whatever. I like equatorials because the marking-out is trivial: 15 deg for each hour. With my newly made burin, I actually did the obligatory Latin motto on this sundial: tempus fugit, or "time flies."

It is hard for us moderns to believe, but in the pre-industrial revolution world, watches were for the very, very, rich. Poorer folk used pocket sundials to tell time. Some even came with a built-in magnetic compass to help you find south. The stylus, however, must point to true south, not mag south. In Willow the magnetic compass points 20 deg and a bit east of true north, towards Hudson bay in Canada, a substantial magnetic declination, as this offset is called. Having consulted the U.S. Naval Observatory, however, I know when the sun will cross the meridian and I find true south that way. See previous sundial post.

I may add that sundials use no batteries, deplete no resources, are fun to make, and, provided that you orient them properly, actually tell time. But if it's cloudy, then you will see why watchmakers made their fortune!

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