The first of these devices is the gnomon, an early sundial. Sundials are considered to be the oldest form of timekeeping, although not in the form in the modern-day design.
The gnomon is essential a large stick place in direct sunlight. The time of day is determined by following the position of the shadow cast by the gnomon.
When the sun roses in the east, the pole will cast a long shadow to the west as the sun is shining directly onto the eastern-facing side of the pole.
As the sun rises in the sky, the shadow will slowly move to the northeast, finally pointing north at noon when the sun is at its highest in the sky, then gradually moving to the southeast as the sun sets, before ending in exactly the opposite position from its position at sunrise as the sun sinks beneath horizon.
The Babylonians and Egyptians divided the day into 12 units, six for sunrise to noon and six from noon to sunset.
Gnomons are used in Egypt in timekeeping for thousands of years. According to hieroglyphics texts, the measurement of time was central to the daily life of ancient Egyptians as early as the Old and the Middle Empires.
Greek astronomers of the Hellenistic period (around 550 BC) used the gnomon, a pole placed in the ground in an open field or area.
Ancient timekeeping device: Gnomon
