sundisk

A sundisk, also known as a sun wheel or sun dial, is a device used to determine the time of day by the position of the sun. It typically consists of a flat, circular plate with markings that indicate the hours of the day. The sundisk is often mounted on a gnomon, a vertical rod or pin, which casts a shadow onto the plate. The angle and length of the shadow change throughout the day, allowing the user to read the time from the markings on the sundisk.

Sundisks can be found in various forms and sizes, from small, portable models to large, permanent installations. They are often used in public spaces, such as parks and gardens, as well as in private residences. Some sundisks are designed to be more decorative, featuring intricate patterns or symbols, while others prioritize functionality and accuracy.

The principle behind a sundisk is based on the apparent movement of the sun across the sky. As the sun moves from east to west, the shadow cast by the gnomon changes position on the sundisk, indicating the passage of time. This method of telling time is known as solar time, which differs slightly from the standard time kept by clocks and watches.

Sundisks have been used for centuries, with evidence of their existence dating back to ancient civilizations such as the Egyptians and Greeks. They continue to be popular today, not only for their practical use in determining time but also for their aesthetic appeal and educational value.