A sun dial is a device that tells the time by using the position of the sun. It consists of a flat plate, called the dial, and a stick, known as the gnomon, which casts a shadow on the dial. As the sun moves across the sky, the shadow moves, indicating the time of day based on the markings on the dial. Sun dials have been used for thousands of years and are one of the oldest timekeeping instruments. They rely on the sun's position, making them most accurate on sunny days. Unlike modern clocks, they do not require electricity or batteries, making them eco-friendly.