The star studded night in the Egyptian sky will not only impress millions of tourists and visitors, it will also provide a unique vista of how ancient Egyptians used their wonderful skills and knowledge of astronomy and astrology to precisely create a calendar that evolved as the first authentic calendar of the modern world.

Just consider those temple priests with their primitive tools and equipments, but still became so successful in identifying almost all the stars and constellations of the universe including the great star, Sirius or Sepdet (local name for Sirius).

The Rise and the Fall of the Great River Nile

To develop a precise and accurate calendar, one needs to use a definite set of data and information concerning the sky and land. Ancient Egyptian priests used a regular event that occurred with an astonishing regularity. This regular event was the rise and fall of the great river Nile that was so regular in its occurrence, which it never failed on its known history.

Here is the regular profile of the great River Nile:

  • Raising water levels around the end of the month of June
  • This period of flood (known as achet in Egyptian language) will last until the end of October
  • This time interval will herald the arrival of rich black mud that is so essential for sowing and growing of crops (also known as peret in Egyptian language)
  • The peak harvest period occurs during the month of February (also called schemu in local language)
  • This period ended with the next Nile flood

However, there was a hitch here! The accompanying floods arrived within the small range of around 80 days that too with highly varying intensities and amplitude. In fact, the timing was too skewed and inaccurate. In Egyptian mythology, people of Egypt perceived a definite connection between Sirius’ appearance in the sky and the onset of Nile floods. In Egyptian myth, people assumed that the tears of Isis caused great floods of Nile and this was due to Osiris’ murder by his brother Seth. In Egyptian mythology, the great star, Sirius was the manifestation of goddess Isis.

The Moon and the Floods

Here is the mechanism of how Egyptians invented their calendar:

The first sighting of new moon that followed the reappearance of Sirius (after its disappearance under the far way horizon) for seventy days was the first day of the New Year and of the initiation of flood period. This was the rule, even if there was no flood.

Now, the skilled priests observed that there four moon sequences within the period that was quite impossible! They also found that a lunar month has 29 ½ days, which ultimately resulted in either short or long years of 12 or 13 new moons!

Thus in the Old kingdom devised a calendar with 12 months of 30 days each. Each month had decades of 10 days.

However, this calendar was too short in order to coordinate with the regular agricultural and lunar calendar. Thus, the priests had to add five more extra days to the calendar called the heriu renpet. This addition was at the end of the year and coincided with local festivals.

However, the ancient Egyptians missed the exact duration of the solar year by almost ¼ day.

Nevertheless, these missing quarter days piled up and accumulated in the course of the time, over thousands of years resulting in one extra day for every four year.

The Sothis Period

Unfortunately, the whole calendar system faltered at the end of a cycle of 1460 years, and the resulting miscalculation was a loss of an entire year. This period is called the Sothis Period.

This little, but serious aberration remained, as it is until the advent of the Emperor Augustus’s period, when he introduced now famous “leap year”. This happened in the year of 30 BC

The Importance of Sirius

However, there is no solid evidence of when Egyptians devised their calendar. There are three recorded evidences of heliacal risings of the great star Sirius:

  • During the period of Thutmosis III
  • During the time of Amenophis I
  • During the era of Sesostris III

Fact: The great Roman historian provides us a valid conclusion that last helical rising occurred on Egyptian New Year during 139 CE.

Now, assuming that the heliacal rising of the star Sirius and the start of the year correspond with the time, when the calendar introduced, one could arrive at a hypothesis that provides three sets of separate years- 1322 BCE, 2782 BCE, or even 4242 BCE, which may form the beginning the onset of a scientifically designed calendar. However, it may be still difficult to assert that the Egyptian calendar’s birth during the fifth millennium BC from the available set of data!

Aberration in the early calculations

There was a definite aberration during the early Egyptian’s calculations; they might have simply failed to note the shift of the calendar though many seasons. Thus, there was a perceived aberration in the system of computing time in years, until the time of Canopus degree of the Great king, Ptolemy III (246 BCE-222 BCE). With this powerful royal decree, he ordered an addition of a day to the calendar, that too every fourth year (corrected, confirmed and corrected by Emperor Augustus). However, the perceived aberration still existed for a log time. By this surgical procedure, it was possible to make the Egyptian calendar as long as the Gregorian calendar.

Fact: It is common for an Egyptian year start on August 29, excepting in those years that precede a Julian leap year, during which the Egyptian year falls on August 30. The shift in the date occurs in a year commonly called the Alexandrinian calendar.

Even with their advanced astronomical skills and knowledge, Egyptians still lacked the system to keep an organized count of years. Egyptians had the habit of writing the number of counting of the livestock that took place every alternating year.

An example: “year of the first counting” or “year of the third time”

The Internal Structure

The internal structure of an Egyptian calendar is simple and straightforward! The entire year divides into three special seasons of four months each. Each moth contains 30 days each. Ancient Egyptians added an additional five days for each year, which makes 365 days in a year. Egyptians had the habit of explaining the events as a sequence of happening.

For example, “2nd day of the third month of the Crowning”

Ache (Inundation)


  • Thot
  • Phaophi
  • Athyr
  • Choiak

Prôje (Winter)


  • Tybi
  • Mechir
  • Phamenoth
  • Pharmuthi

Shômû (Summer)


  • Pachon
  • Payni
  • Epiphi
  • Mesori

The Thirteenth Month

There is a particular month called epagomenai that is actually the thirteenth month of the Egyptian Calendar. Ptolemy named the era as the Era of Nabonassar with epoch 26 February 746 C.E. However, there are several others eras that formed the basis of Egyptian calendar.

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