History

Astronomy in ancient Egypt

Astronomy in ancient Egypt

The Egyptians observed that the stars make a complete turn in just over 365 days. In addition, this 365-day cycle of the Sun agrees with that of the seasons, and before 2500 B.C. the Egyptians used a calendar based on that cycle, so it is assumed that they used astronomical observation systematically since the fourth millennium.

The Egyptian calendar year had 12 months of 30 days, plus 5 days called epagómenos. The difference, then, was ¼ day compared to the solar year. They did not use leap years: 120 years later a month advanced, so that 1456 years later the civil and astronomical year coincided again.

The Nile began its rise more or less at the moment when the star Sothis, our Sirius, (the Sepedet of the Egyptians), after being long invisible under the horizon, could be seen again shortly before the sun rose.

The Egyptian calendar had three seasons of four months each:
- Flood or Akhet.
- Winter or Peret, that is to say, "exit" of the lands out of the water.
- Summer or Shemú, that is, "lack of water."

The opening of the Egyptian year occurred on the first day of the first month of the Flood, approximately when the Syrian star began to be observed again a little before sunrise.

From the end of the Egyptian era (144 A.D.) are the so-called Carlsberg papyri, where a method is collected to determine the phases of the Moon, from very old sources. They establish a cycle of 309 moonings for every 25 Egyptian years, so that these 9,125 days are arranged in groups of lunar months of 29 and 30 days. The knowledge of this cycle allowed the Egyptian priests to place lunar mobile parties on the civil calendar.

The orientation of temples and pyramids is another proof of the type of astronomical knowledge of the Egyptians. Pyramids such as Giza's were built, aligned with the polar star, with which it was possible to determine the beginning of the seasons using the position of the pyramid shadow. They also used the stars to guide navigation.

The legacy of Egyptian astronomy reaches our days in the form of the calendar. Herodotus, in his Stories says: "the Egyptians were the first of all the men who discovered the year, and said they found it from the stars."

The insightful observation of the stellar and planetary movement allowed the Egyptians to draw up two calendars, one lunar and the other civil. The Julian calendar and, later, the Gregorian - the one we use today - are nothing more than a modification of the Egyptian civil calendar.

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