Sundials, devices that tell time by the position of the sun, are perhaps the world’s oldest garden ornament.
Sundials are referenced in the Old Testament as far back as 700 BC. and have been used as time telling devises for centuries. The height of the sundial’s popularity was the 17th through the early 20th century, when elaborate sundials – usually made of brass or bronze – were prominently displayed in many gardens.
Sundials today are mostly utilized as decorative accents, but it is kind of fun to understand how they can be used as time pieces.
How Sundials Work
A long thin rod or a triangular shaped element (called a gnomon) with a straight edge and a point (called a style) casts a shadow onto a flat surface that is marked with lines indicating hours of the day. Place your sundial in an area where it will receive full sun, with no large plants casting shadows on its face. It can be placed either directly on the ground or on a pedestal, and it must be level to be accurate.
How to Set Your Sundial
For the best accuracy, your sundial should be set on one of the four dates of the year when solar time and clock time align: April 15, June 15, September 1 and December 24. However, you can set yours up on any day of year if you are not concerned with absolute accuracy. Set your sundial at noon on a sunny day, with the rod (gnomon) pointing to the North. Positioned this way, you should see no shadow at noon. The shadow should fall on the numbers of the dial to approximate the time of day as the sun moves across the sky, casting a shadow to the left of the gnomon in the morning, and to the right in the afternoon.