How Does a Sundial Tell Time?
Long before we had clocks, people used sundials to tell time. A sundial tells time by measuring the angle of a shadow cast by the sun. A sundial face is divided into hours.
When the sun strikes the pointer in the center of the dial, it casts a shadow on the dial face. The time is told by the shadow of the pointer falling on the different numbers as the sun moves across the sky.
The ancient Egyptians made the earliest known sundial in about 3500 BC. This sundial was simply a stick or a pillar that cast a shadow on the ground. The ancient Greeks made a sundial with a bowl-shaped opening cut into a block of stone or wood.
A pointer in the center cast shadows inside the bowl. Muslims later invented the modern sundial—the type with the angled gnomon.
A sundial can’t tell the time at night, nor can it tell the time when the sun is hidden by clouds. It is no wonder that people worked out a better way of telling time with clocks.