Last week, we saw how the Ancient Egyptians, more than 5,000 years ago, created their calendar by dividing the year into 12 months of 30 days each (plus an additional 5 or 6 days of festivities) and three seasons, each season consisting of four months and each month divided the month into 3 decans (weeks of ten days’ length).
Up until a few centuries ago, different nations divided the day into 12 hours and the night into 12 hours. The Ancient Egyptians were the first to divide the day and night into 12 hours each and thus creating the notion of 24 hours for the full day. How did the Ancient Egyptians determine the hours of the day or the night?
During the day, they used a sundial which had a block of small cubical stone in the middle, aligned to the four cardinal points. The block threw its shadow in one direction for half of the day (from sunrise to noon) and then in the other direction in the other half (from noon to sunset).
The space to the right and to the left of the stone had six marks or lines of unequal spaces indicating the six hours of the first half of the day and the second half of the day respectively. One of these sundials is in the Egyptian museum.
During the night, the Ancient Egyptians used to determine the hours by observing the sky. They have established tables for the hours of the night by observing the setting of a series of stars. As the Earth revolved around its axis, the dome of the sky above their heads apparently rotated in the opposite direction; accordingly, the chosen series of stars, part of the zodiac constellations, set one after another at intervals of one hour. One of these tables was found on the sarcophagus of Emsaht from the Middle Kingdom. It’s now exhibited in the Egyptian museum.
Both the sundial, used to determine the time during the day, and the observation of the sky, which determines the hours during the night, were dependant on having a clear sky. If it were cloudy, then both the day observation and the night observation were affected and were maybe even impossible. To overcome this problem, the Ancient Egyptians invented a third method to determine the time – a water clock or ‘clepsydra’ (literally a water thief).
The Ancient Egyptian water clock is in the form of an alabaster vase with an orifice near the bottom. As it is filled with water, the water starts flowing from the orifice and the level of the water falls with time.
On the inner wall of the vase there is a vertical row of twelve equally spaced dots to indicate the twelve hours of the day (or the night), since the length of the day is not equal for the different months of the year. There are twelve such rows of dots representing the twelve months.
In the Egyptian Museum, there is a beautiful example of such a water clock that dates from the time of King Amenhotep III (1380 BC) and there is an inscription on it which states that its purpose is “to know the hours of the day when we cannot see the god Ra’ (the sun) and to know the hours of the night, when stars are invisible”.
