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The Human Sundial
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The Human Sundial
by Debbie Boulton

For thousands of years man has utilized the sun to tell time, beginning with the simple observation that shadows change both in direction and length throughout the day. The rotation of the earth gives us day and night, and the movement of the earth around the sun gives rise to our seasons. Mathematicians in the ancient civilizations of Greece, Rome, and Egypt studied the behavior of shadows and applied their knowledge to construct the earliest known sundials. Until the 19th century, when clocks and watches became common, sundials were the preferred method of telling time.

What are the benefits of installing a sundial on a school yard? Certainly there are direct ties to curriculum learning (for example, Astronomy in Grade 6 Science, Light and Shadow in Grade 4 Science). But a sundial also provides students with an interactive link to the natural world. In today's high-tech society, our awareness of seasonal changes and the position of the sun in the sky are no longer key to our survival. A sundial gives students an opportunity to observe firsthand daily changes in our natural environment.

A sundial consists of two elements: a dial plane which is a flat surface marked with the times of the day, and a gnomon, often a piece of metal which casts a shadow onto the dial plane. A human sundial is unique in that the gnomon is a person! When standing in the correct position, the person's shadow will indicate the time.

The human sundial (more correctly called an analemmatic sundial) can be installed on almost any concrete or asphalt surface in a schoolground. The surface must be flat, approximately 5 metres by 5 metres in size, and must receive direct sunlight during the hours of intended use. The only other materials required are concrete paint, paint brushes, and a template for positioning the times and standing positions.

Details of the Analemmatic Sundial

Installing an Analemmatic Sundial

Equation of Time

References

Appendix