Measuring time by the Sun

For thousands of years, people used sundials to tell the time. The first sundials were used more than 3,500 years ago in Egypt.
A sundial is a device that measures time by the position of the Sun.
In common designs such as the horizontal sundial, the sun casts a shadow from a thin rod or a sharp, straight edge, onto a flat surface marked with lines indicating the hours of the day.
As the sun moves across the sky, the shadow-edge progressively aligns with different hour-lines on the plate.

Clic here to see a patent of a modern adjustable sundial.



How to make a sundial on your own