Ancient Egyptian civil calendar

     The Egyptian civil calendar followed the cycle of the Nile's yearly flooding, on the 19th day of July of the Julian calendar. From this day that can be defined as the first of the year, the agricultural activities were divided into three seasons of four months:


Flood………………….AJET season         

Sowing……………….PERET season      

Harvest………………SHEMU season      


     The calendar consisted of 365 days, divided into 12 months of 30 days, totaling 360 days; the other five days between the last day of Mesut-Ra and the first day of Renpet, first month of the year, were the feast days called Heru-Renpet, (Greek Epagómenos), as shown in the following table:


     This calendar of 365 days, more or less of the same length of the solar, is called Sothic because it is based on the heliacal rising 30 minutes before dawn, of the star  spdt (Sopdet: Dog Star), the Sothis of the Greeks and our Sirius; a star of 1.46 magnitude, spectral type A1, that belongs to the constellation Canis Major.

An inscription reads:




     After a long interval of 70 days, this astronomical event can be seen from the first day of the summer solstice to the next spring equinox. Since the heliacal rising of the star is verified through a cycle of 365.25 days, the Egyptian civil calendar fell behind one day every 4 years.

    The coincidence of the heliacal rising of Sirius and the first day of the Sothic calendar only happened once every 1460 years. (365 : 0.25 = 1460)



     The “ideal” Egyptian year was that in which the overflow of the Nile coincided with the rise of Sothis, 30 minutes before dawn, but since the Egyptians never introduced the leap year, the New Year feast linked to the rise of Sothis, inevitably moved the calendar. This “ideal” year was repeated only every 1460 years.

     The fact that the Egyptian priests took into account the shift in the calendar of the heliacal rising of Sirius, allows establishing a more or less exact date of the information contained in some archaeological records, which indicate the month and day of the heliacal rising of Sirius in the reigning year of the sovereign. This information would have no chronological interest without the clarification of the Roman grammarian and writer Censorinus, who lived in the second half of 3rd century; he reveals that the heliacal rising of Sirius took place in Heliopolis, on the first day of the Egyptian calendar, the year 139 AD, in the 19th of July of the Julian calendar. (De Die natali Liber ad Q. Caerellium XXI 10) (1)


     The town of Heliopolis, “Mehret Innu”, was an important astronomical center, where the high priest bore the title of chief of the astronomers: “Ur-Mau”. Assuming that during the whole of the Egyptian civilization, the heliacal rising of Sirius was observed from Heliopolis by the priests, the years in which the same coincidence was verified can be calculated; this makes it possible to estimate the date of the rising of Sirius mentioned in several archaeological records, according to the Egyptian year cycle and the Julian leap year cycle.

    However, we have to remember that from the XVIII dynasty, the observing point of heliacal rise to calculate the year, was transferred from Heliopolis to Waset / Thebes (Luxor), and because of this, the heliacal rise noted in the papyrus Ebers probably refers to Waset / Thebes.
     (1547 Heliopolis BCE, 1527 BCE Waset / Thebes)

     From a chronological point of view, the main date information concerns to:


1   The 7th year of reign of Sesostri III, 16th day of the 4th month of Peret, which allows to establish the astronomical event in 1879 BC, and therefore the coronation of Pharaoh in 1886 BC (Papyrus Berlin 10012) (2)


2  The 9th year of the reign of Amenhotep I, 9th day of the 3rd month of Shemu, which allows to establish the astronomical event in 1527 BC, and the coronation of the king in 1536 BC. (Eber Papyrus) (3)


3  The 20th year of the reign of Thutmose III, 28th day of the 3rd month of Shemu, which allows to establish the astronomical event around the year 1471 BC. (Stellae of Elephantine) (4)


    Censorinus wrote that the heliacal rising of Sirius in 139 of our era, happened on July 19th. As the cycle of the heliacal rising of Sirius is equal to 365.25 days, it can be said that during the whole time the Egyptian civilization, the event has always been verified on July 19th of the Julian calendar.

   Today, the heliacal rising of Sirius is presented in Cairo, (the same location as the ancient Heliopolis), on August 3rd. This is not due to an astronomical phenomenon but to the fact that the new Gregorian calendar canceled 10 days of the year 1582, plus three days (29 February) of the centuries 1700, 1800 and 1900, being secular years not divisible by 400.

    Since the day of the heliacal rising of Sirius anticipates or postpones nearly one day for each degree of latitude, above or below, in the northern hemisphere the heliacal rise of Sirius takes place on June 21st, that is at the beginning of summer, while in the southern hemisphere, at the onset of winter.



     In the year 238 AD, the grammarian and writer Censorinus gave as a birthday gift to his superior Cornelius, the treatise De Die Natali. Q. Liber ad Caerellium, in which he says that 100 years earlier, under the consulship of Antoninus Pius, that is, in 139 AD, the first day of the year, that is, the 1st of Thoth on the Egyptian calendar, corresponded to “ante diem XIII kal. Aug.” (July 19th of the Julian calendar).

(Thoth is the Coptic name, the Egyptian name is Dyehuty)




      Another important Sothic date is in the Berlin Papyrus 10012a, found by Borchardt in Kahoun, in 1899.





     The Ebers Papyrus, called by the name of its European buyer, is a papyrus roll of 20 meters long by 20 cm wide; it is subdivided into 108 pages and dated as belonging to the eighteenth Egyptian dynasty (~1561 BC), more precisely, to the reign of Amenhotep I, even if the text could be far more ancient. It was purchased in Thebes by Georg Ebers, in the winter 1873-74, and is now preserved in the library of the Leipzig University, in Germany. The second of the three absolute dates for the Egyptian chronology is found in this papyrus, as shown in the following table:


     The stele of Elephantine, of which a fragment is preserved, is a calendar of the religious festivals in the temple of Elephantine, at the time of Thutmose III of the XVIII dynasty. It records the heliacal rising of Sirius on the 28th of the 3rd month of Shemu (Apep).

According to astronomical calculations, the event was observed around 1471 BC

                 Flood………………….AJET season  

                               Sowing……………….PERET season  

                               Harvest………………SHEMU season