There are a few basic reasons why your sundial may not indicate standard clock time. Sundials available today have generally been designed for a given latitude. The style or gnomon must be set in alignment with true North while the angle that it makes with the horizontal should equal the specific latitude where the sundial is located. To insure that this angle is correct the sundial may need to be slightly tilted along its North/South axis. A correction for the actual longitude of the sundial compared with the longitude of the official time zone may be necessary. The hour-lines must be rotated by an angle that equals the difference in longitudes.
The sundial’s time differs from standard clock time also because the earth’s orbit around the sun is elliptical and because the earth tilts on its axis. The distance between the Earth and the Sun actually varies, and the correction for this ranges from zero minutes to as much as a quarter hour either early or late. On some sundials the “equation of time,” which describes the correction, is inscribed on a plaque attached to the dial. In very sophisticated sundial designs the equation is incorporated automatically.
In areas where daylight saving time is used, the sundial time will be off by an hour. This is often corrected by use of two sets of numbers on the dial rather than just one. With a little patience and perseverance your sundial can be situated so that its accuracy is totally satisfactory.
Tags: brass sundial, bronze sundial, garden sundial, gnomen, sundial, sundial clock
