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Egyptian Calendars and Clocks

    The first working and usable calendar was the ancient Egyptian calendar, which dates back as far as 4236 B.C. The ancient Egyptian calendar was based on the moon's cycles, and the Egyptians regulated the calendar by using the stars. Eventually, they began using the stars more than the moon because the stars were more accurate in predicting the seasons of the year. The ancient Egyptians observed that a group of stars--which we call Sirius or "Dog Star" in Canis Major--rises next to the sun every 365 days. Of course, 365 days is the length of time it takes for the earth to revolve around the sun once--what we call one year. The ancient Egyptians noticed that this always occurred a few days before the annual flooding of the Nile River. This type of calendar allowed them to accurately predict when the Nile would flood, which helped them with their crops. Ultimately, they used 36 stars to mark out the year.

    The Egyptian people realized there was a difference between the number of days in a calendar using the moon and the number of days in a calendar using the sun. When they realized this, they were able to devise a 365-day calendar. They divided the year into three seasons of four months. Each month had 30 days. If you do the math, you'll find that 12 months x 30 days per month makes only 360 days. To complete the year, they added five special days at the year's end.

    For more than 2,000 years, the Egyptians used three different calendars for different purposes. The most accurate calendar was based on the stars, and Egyptians used this calendar to help them plant and harvest crops. Another calendar used the sun to keep track of days throughout the year. And an older calendar used the moon to observe Egyptian festivals.

    The Egyptians also influenced other ancient calendars. When Julius Caesar visited Egypt, he met an astronomer named Sosigenes who explained the Egyptian calendar to him. The Romans used the Egyptian calendar to help them develop the Julian calendar. This Julian calendar served Western Europe for more than 1,500 years.

    The Sumerian culture was lost without passing on its knowledge of time. The Egyptians were the next group of people to divide their day into parts, similar to our hours. About 3500 B.C., Egyptians created a slender four-sided tapering monument called an obelisk, which cast shadows. By looking at the obelisk's shadows, people could tell when noon occurred and, thus, divide their day into two parts. Later, the Egyptians added markers around the base of the obelisk to indicate more divisions of time throughout the day. These divisions are similar to our hours.

    Another shadow clock or sundial came into use around 1500 B.C. to measure the passage of "hours." This clock was oriented east and west in the morning. An elevated crossbar cast a moving shadow on the "hour" markers. At midday, Egyptians turned the device in the opposite direction to measure the afternoon "hours."

    The ancient Egyptians even learned to keep track of time at night. An instrument called a merkhet was developed in 600 B.C. It is the oldest known astrometrical tool, which is a tool to measure the positions, movements and distances of planets and stars. Egyptians lined up a pair of merkhets with a certain star, called the Pole Star, to establish a north-south line. The Egyptians used the merkhets to mark off nighttime hours by determining when other stars crossed the meridian. Not bad for a people living 2,600 years ago! 
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