Principles of Science: Rotation of Earth

Look at the large scale sundial here. On a sunny day, the markings are positioned so that the shadow cast by the sundial will provide the time of day.

Not too long ago, man believed that the sun revolved around the earth; to the human eye this appears to be true. Practically four thousand years ago, people started using the apparent motion of the sun in the sky to tell time. They built instruments called sundials, which cast a shadow on the ground. The direction of the shadow depends on the location of the sun in the sky. People then indicated on the ground the time of the day so that the shadow of the sundial’s pointer pointed to the correct time.

Sundials were common through the Greek and Roman periods, but ironically, as soon as sundials were perfected, mechanical clocks were also developed and the sundial fell into the obscurity of private gardens and the occasional public plaza.