The sundial: the original clock

Sundial
Sundial

The oldest of timepieces is the sundial. Around 4000 B.C. the ancient Egyptians used a gnomon (projection rod), stuck vertically into the ground, to tell the approximate time of day by the position and length of the shadow it cast. This is thought to be the origin of the sundial.

Egyptian portable sundial
Egyptian portable sundial
Obelisk
Obelisk
Shadow cast by the gnomon standing on the ground (schematic view)
Shadow cast by the gnomon standing on the ground (schematic view)

In the northern hemisphere, in which Egypt is located, the shadow cast by a gnomon erected on the ground moves in an arc from left to right. It is thought that the reason the hands of a clock rotate to the right is because the sundial originated in the northern hemisphere.

Here is some additional information