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| This replica of an ancient Egyptian water clock is based on the original version carved from alabaster stone. There are ten columns of twelve indentations around the inside of the clock. As water drained from a hole in the bottom at a regular rate, more indentations became visible. People could tell how much time had passed. |
Timekeeping was important to people in ancient Egypt. Priests and soldiers had to perform certain tasks at certain times. Rulers, government officials, and scribes had to keep track of workers and their time on the job.
Like the Babylonians, the Egyptians divided daylight into twelve equal parts. The Egyptians used clocks as early as 3500 b.c. The first Egyptian clock was an obelisk, a tall, four-sided pillar. It cast a shadow as the Sun moved past. The shadow grew shorter throughout the morning as the Sun rose in the sky. It disappeared at noon with the Sun directly overhead. The shadow lengthened throughout the afternoon as the Sun dipped in the western sky.
People estimated the time based on the length of the shadow. Sometime around 1500 b.c., the Egyptians made a new and improved sundial. It looked like the letter T stuck in the ground. A long, narrow base extended behind it along the ground. Lines on the base marked the hours.
Egyptians could tell the time of day by looking at which line the bar’s shadow reached. Later, they used sundials in the shape of half circles, like those used in the ancient Middle East. As the Sun moved through the sky, a gnomon cast a shadow on lines spreading out from the center. These early sundials marked twelve hours of daylight year-round. But in Egypt, as in
most places, the amount of daylight changes with the seasons. So the length of hours actually varied. With this technology, an hour wasn’t a standardized measure of time. Each hour was longer in the summer and shorter in the winter.
Also around 1500 b.c., the Egyptians built another kind of timekeeper. It was the clepsydra, or water clock. It was made of a clay jar with markings on the inside. Unlike sundials, water clocks could keep time at night. As water in the jar dribbled out of a small hole at the bottom, more and more markings were exposed. Each mark that showed meant that another unit of time had passed. Clepsydras had to be made very precisely so they all kept time the same. Water had to flow out of each one at about the same rate.
Like the Babylonians, the Egyptians divided daylight into twelve equal parts. The Egyptians used clocks as early as 3500 b.c. The first Egyptian clock was an obelisk, a tall, four-sided pillar. It cast a shadow as the Sun moved past. The shadow grew shorter throughout the morning as the Sun rose in the sky. It disappeared at noon with the Sun directly overhead. The shadow lengthened throughout the afternoon as the Sun dipped in the western sky.
People estimated the time based on the length of the shadow. Sometime around 1500 b.c., the Egyptians made a new and improved sundial. It looked like the letter T stuck in the ground. A long, narrow base extended behind it along the ground. Lines on the base marked the hours.
Egyptians could tell the time of day by looking at which line the bar’s shadow reached. Later, they used sundials in the shape of half circles, like those used in the ancient Middle East. As the Sun moved through the sky, a gnomon cast a shadow on lines spreading out from the center. These early sundials marked twelve hours of daylight year-round. But in Egypt, as in
most places, the amount of daylight changes with the seasons. So the length of hours actually varied. With this technology, an hour wasn’t a standardized measure of time. Each hour was longer in the summer and shorter in the winter.
Also around 1500 b.c., the Egyptians built another kind of timekeeper. It was the clepsydra, or water clock. It was made of a clay jar with markings on the inside. Unlike sundials, water clocks could keep time at night. As water in the jar dribbled out of a small hole at the bottom, more and more markings were exposed. Each mark that showed meant that another unit of time had passed. Clepsydras had to be made very precisely so they all kept time the same. Water had to flow out of each one at about the same rate.
Calenders
The solar year is the time Earth takes to travel around the Sun. It takes approximately 365 days, five hours, forty-eight minutes, and forty-six seconds. What would happen if the calendar didn’t match the solar year?
Holidays and seasons would gradually shift. Summer months would eventually fall in the middle of winter. The first ancient calendars did shift in this way. They were created according to the lunar year. The lunar year is divided into twelve months based on the phases of the Moon. It lasts only 354 days. Because of the difference between the lunar year and the solar year, the first calendars were not very accurate. They shifted 110 days—almost four months—every ten years. The Egyptians were the first people to solve the problem. They created a calendar based on the solar year. The Egyptian calendar had twelve months of thirty days each, with five extra days added at the end of each year. In 238 b.c., the pharaoh Ptolemy III made the calendar even more accurate. He added an extra day every fourth year. That day made up for the nearly sixhour difference (about one-quarter of a day) between the calendar year and
the solar year. A year with an extra day is a leap year.
Holidays and seasons would gradually shift. Summer months would eventually fall in the middle of winter. The first ancient calendars did shift in this way. They were created according to the lunar year. The lunar year is divided into twelve months based on the phases of the Moon. It lasts only 354 days. Because of the difference between the lunar year and the solar year, the first calendars were not very accurate. They shifted 110 days—almost four months—every ten years. The Egyptians were the first people to solve the problem. They created a calendar based on the solar year. The Egyptian calendar had twelve months of thirty days each, with five extra days added at the end of each year. In 238 b.c., the pharaoh Ptolemy III made the calendar even more accurate. He added an extra day every fourth year. That day made up for the nearly sixhour difference (about one-quarter of a day) between the calendar year and
the solar year. A year with an extra day is a leap year.
Source: Ancient Computing technology, Michael Woods and Mary B. Woods
1 Comments
This ancient Egyptian "water clock" (clepsydra) means that the ancient Egyptians had a clear idea on the calculations involved in water reservoir drainage 3500 years before Torricelli's theorem based on Bernoulli principle of conservation of hydraulic energy, and more importantly this water clock (clepsydra) proves once again that they had known a precise value for the engineering "pi" ratio of the circle since knowing this ratio is needed to make the hourly indentation of 12 hours inside such a truncated cone clepsydra.
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