Making a Sundial

Get back in touch with natural timekeeping by making a sundial — civilization's first clock.

| May/June 1981

While a clock is actually little more than a mechanical or electronic contraption that mimics the temporal progression of the earth's revolution about its axis, perusing the timepieces in a typical jewelry store's display cabinet suggests the business of telling time has become bewilderingly complex in our "digital age." One informal study recently found that half of a group of Ph.D.'s weren't even able to operate one particular watch without referring to the owner's manual. (In fact, the chronometer's manufacturer suggests that wearers always carry their instruction booklets along!)

It's puzzling that devices conceived to ease humankind's burden (by substituting gears and/or circuitry for human calculation) have come full circle and are now harder to use than were the first clocks: sundials. And in truth, much of the ciphering that is necessary to tell time accurately with a sundial has resulted from our complex man-made system of time zones (which often fail to follow meridians—and, therefore, the progression of the globe's revolution—accurately), the creation of mean solar time, and the vagaries of "daylight-saving time," all of which can be seen as questionable meddlings in our daily dealings with the sun.

Whether your interest in making a sundial stems from a reaction to the arbitrary way we've come to look at the concept of time, historical curiosity, a desire to get a little closer to the ways of nature, or just a love for the uncomplicated workings of a "helioclock," we think you'll find the device an interesting project that will produce an attractive (and useful) addition to your yard or garden.

Getting the Lay of Your Land

In order to lay out the sundial face, you'll need to know your location in terms of latitude and longitude. So start the project by consulting an atlas to find out where on the world you are. Latitude lines run across the map, from east to west (or vice versa) and will be marked "North" if you live above the equator. Longitude marks run north-south and will be designated as "West" if you are located in the Western Hemisphere. (Please note that all of the rest of the instructions in this article apply only to the Western Hemisphere, north of the equator.)

Laying Out the Dial Face

At this point you should decide how large a sundial you wish to build. Faces can be designed in any reasonable size (though larger dials allow more accurate readings), but we chose a 9"-diameter circle because a 1 1/2"—deep, 9"-wide cake pan provided us with a very convenient mold. The diameter of your "clock's" face will become Dimension A.

The other dimension needed to lay out your sundial can be calculated by first drawing a semicircle using Dimension A as the diameter. Construct a tangent perpendicular to the diameter of the half circle, and then scribe a line that diverges from the intersection of the diameter and the tangent at an angle equal to your latitude. The length of the chord which is described by that line's intersections with the semicircle will become Dimension B.

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