The oldest sundials

As the Sun moves across the sky, the shadows cast by objects change in length and direction. By placing an object in the ground, you can use these shadows to chart the passage of the day. By scratching lines into the earth, our ancestors could define an ‘hours’ system and begin to count the passing of daylight hours for the very first time. And so we have a sundial—a time-finder.

The 12-hour day that we are familiar with can be traced back to ancient Mesopotamia and Egypt. And the oldest known sundial dates from the reign of Thutmosis III, who ruled Egypt around 1500 BCE. It is a simple L-shaped piece of stone with hour lines scored out along its upper face. At dawn, it would have been aligned towards the rising Sun, and a bar mounted atop the short part of the L would have cast a shadow on the first hour line of the day.

As the Sun moved, the position of the shadow progressed along the hour lines, until noon, when the direction of the sundial was reversed and the same six hour lines where used to count out the afternoon hours.

Credits. From 'Telling the Time with the Sun', Science Museum, London, 27 September 2018.