THE PATH TO MY FIRST POCKET SUNDIAL
Many years ago, I read an article in the May/June 1982 Mother Earth News by Carmen E. Trisler, who made tiny sundials inside aspirin tins. The idea was that you could make it small, carry it around in your pocket, and then just set it up somewhere when you wanted to know the time, during daylight hours.
But since I never buy aspirin, it didn’t make sense to buy the container of aspirin just for the tin, and I saved the article for years in one of my many files.
Then one day it happened! A worker who was doing some carpentry at our home discarded an empty aspirin tin in my trash can. I picked it out as soon as I spotted it, knowing I could now proceed with this long-awaited project.
With the tin in hand, I quickly shuffled through my files of clippings, trying to find the old article. Amazingly, with my eclectic system of filing, I found it! The article described how to make a useful sundial that folds into an aspirin tin. All I had to do, the article proclaimed, was to cut out (or copy) the dial face from the magazine, mount it onto stiff thin cardboard, and then put it into the tin. A simple one-size-fits-all sundial!
I made a photocopy of the dial face, as well as the gnomon (pointer), secured them both to stiff thin cardboard, and cut them out. That done, all I had to do next, according to the magazine article, was to attach the gnomon to the dial face, set the sundial on a flat surface in a sunny location, and align it to true north with my compass.
All this done, I was now supposed to be able to simply read the time by observing where the top of the gnomon’s shadow appeared on the dial face. Wrong! The time on my dial face was nearly an hour wrong, even though I had already taken Daylight Saving Time into consideration.
I then carefully reread the old article, and noted that its author stated the sundial would provide “approximate time.” But I wasn’t satisfied with approximate time. After all, I can guess within an hour of actual time by merely glancing at the position of the sun.
To be fair, the Mother Earth News editorial note said that this sundial was a “crude toy,” and that the readers could purchase a back issue of the magazine that provided more details. So I then began my serious research into the intricacies of accurate sundials.
DOING THE MATH
I obtained a few books for my research, including college-level astronomy texts. At first, I was dazzled at the seemingly complex mathematical formulae involved in making even the simplest sundial. But after I did it a few times, it all started to make more sense.
I should state right away that there are many ways to make an accurate sundial. I am sharing one way, the way that I found made the most sense to me.
The dial face for any given location is drawn based upon the latitude of that location. The gnomon’s top angle must be the same number of degrees as your particular location is above the equator. (The gnomon is the part of the device that casts the shadow on the dial face.) For example, if you live at 34 degrees latitude, your gnomon’s top angle must be 34 degrees. That is, each sundial is always made for the particular location where you intend to use it. There is no such thing as a sundial you cut out of a magazine that will be accurate everywhere.
When the final dial face is drawn, it should accurately read the time. I say “should” because mine did not. When I put the sundial face into my aspirin tin and attached the gnomon, my times were still as much as 30 minutes off. Now what?
Part of the problem with a small sundial is that even the smallest error is magnified greatly. So I carefully redrew the sundial face, taking extra pains to draw the lines as precisely as possible. I used a fine pencil and a fine straightedge, and I drew everything twice as large as the aspirin tin.
Then I took my new drawing to a photocopy shop, and had it reduced 50 percent. I covered it and the gnomon with wide plastic tape (for weather protection), and I assembled it all into the aspirin tin.
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