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Astronomy was very important to the ancient Egyptians, who observed the sky periodically. The astronomers named what they saw in the sky and used their observations to create the Egyptian calendar. The beginning of the Egyptian year was declared when there was a flood, as they noticed that the flood begins with the star Sirius, also known as the Dog Star, the brightest star in the sky. This incident represented the beginning of the agricultural year in Egypt. The year had 365 days divided into 12 months and each month had 30 days. They made the remaining five days feast days, called the Epagomenal Days, or the days upon the year, and added them at the end of the year. Months of the year were divided into three seasons, namely: the flood season, the planting season, and the harvest season. The year, the season, the month and the day in which the king assumed power was usually recorded by the Egyptians in their documents.

The ancient Egyptians used instruments or indicators for observing the circumpolar star. They would then draw a north-south axis line on the ground marking its direction, which was required for the proper orientation of important building projects. One of the instruments used was called "Merkhet," which could mean "indicator." It consisted of a horizontal, narrow wooden bar with a hole near one end, through which the astronomer would look to fix the position of the star. The other instrument, called the "bay en imy unut," or palm rib, had a V-shaped slot cut in the wider end through which the priest in charge of the hours looked to fix the star.

In the Greco-Roman era, Claudius Ptolemy, an astronomer, mathematician, and geographer, worked from the data of past astrologers to map over 1,000 stars. He compiled a list of 48 constellations and described the longitude and latitude lines of the earth. He was a believer that the earth was the center of the universe and worked to advance this theory. He developed the Ptolemaic system to explain why some planets seemed to move backwards for periods of time in their orbit around earth. He theorized that each planet also revolved in a smaller circle as well as a larger one. This was called the "epicycle." This theory would survive for 1400 years, until it was finally accepted that the earth was itself another planet in orbit around the sun.

The Greco-Romans used a calendar based on the Julian calendar calculations that used the leap year. Egyptian Christians, called Coptics, adopted this calendar to follow the sun and calculate the days, seasons, and solar years. The lunar year was also important to the Coptics, whose lunar calendar was used to determine the date of Easter and other important religious holidays. The Greco-Roman period also saw the invention of the astrolabe, a navigational tool that was perfected during the Islamic era. The astrolabe played an important role in guiding ships, whether for military or commercial purposes.Ancient Egyptians were concerned with the annual cycle of the seasons to establish the time for cultivating and harvesting.

For certain individuals, however, time was extremely important; these were the astronomers and priests who were responsible for determining the exact hour for the daily rituals and for the important religious festivals. Sundials, which allowed the astronomers and priests to observe the passing of the 12 daylight hours, could not be used to record the 12 nighttime hours.

A man called Amenemhat created the first water clock in the time of Amenhotep the First. The water clock enabled the Ancient Egyptians to measure the passing of every 12 hours, both night and day, winter and summer.

Water Clock

This alabaster water clock of King Amenhotep the Third has 12 carved columns of 11 false holes, corresponding to the hours of the night.

The water flowed through a very small hole made in the center of the bottom, emerging on the outside under the figure of a seated baboon. To know the time, one had to look inside the basin to observe the water level and read the time according to the nearest false hole.

The outside surface of this clepsydra, or water clock, is decorated with figures and text that show symbols of certain planets and constellations and give a list of the protective spirits for each of the ten days of the ancient Egyptian week.

The middle register, or section, is occupied by the circumpolar stars under the aspects of various gods and animals.
Dimensions:  Height 95 cm  Diameter 48.5 cm

The Coptic Calendar

Egyptian Christians mark the 29th of August, AD 284, the day many became martyrs, as the beginning of their history. They used the same calendar that had been employed in Egypt before that time. It was based on the Julian calendar calculations that implemented the leap year, following an order from Julius Caesar in 46 BC It is named the Coptic calendar or the martyrdom calendar.

The Coptic calendar follows the sun and calculates the days, seasons, and solar years according to the earth's orbit around the sun.

As science advanced, the Egyptian Christians began to record the difference between one moon's course and another, the average time of a moon's course, and the time between the appearance of a new crescent and the following crescent, which is known as the lunar month.

The Coptic lunar calendar was based on rules set by the Greek astronomer Meton in the fifth century BC, which state that every 19 solar years is equivalent to 235 whole lunar months without any fractions.

The Copts have used this rule since the third century AD to determine Easter as the Sunday following the first full moon after the spring equinox.

Westerners applied these calculations to the Roman calendar. As a result, all Christian festivals were held at the same time, until 1582 when the Westerners adjusted their calendar to that of Pope Gregory XIII.

The Coptic calendar follows the same system as that of the ancient Egyptian calendar and remains an important reference. Because it is accurate in its forecasts of weather conditions, the seasons, agriculture, and the Nile flooding, farmers still use the Coptic calendar.
A day tour to visit Dendera Temple where the most preserved scenes of The ancient astronomy has been recorded on its giant walls .Please Click Here.


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