What is Astroarcheology?

Archeoastronomy is a multidisciplinary scientific study how ancient cultures understud and used astronomy. Many ancient monuments are aligned to stars or solar events like equinox or sun-rise.

Orion Constellation Theory Pyramid Sirius Star alignment

The proposed alignment of the Great Pyramid of Khufu. The shafts shall point to star constellations in c. 2600 BC (e.g. The Orion Constellation Theory of Robert Bauval)

Dageno, Orientaciones de los llamados canales de ventilación de la gran pirámide. Alfa Draconis, Osa Menor, Orión y Sirio, Relabeling in English, CC BY-SA 3.0

There are many examples of aligned monuments, e.g. Newgrange passage tomb (Ireland), Uxmal, El Caracol in Chichen Itza, the Pyramids of Giza, Dashur, Abusir, Stonehenge or Chaco Canyon..

There are also ancient texts (like the Pyramid texts) referring to astronomy and mechanical objects like the Antikythera-mechanism, testifying for a great knowledge and skill of the ancients and the observation of the sky in the past.


The Discovery:

The oldest Sothis date of ancient Egypt


July 31st, 2014 about 3pm a new Sothis date was discoveredy by Prof. Rainer Hannig. Dr. Michael E. Habicht and Daniela Rutica M.A. in a small museum in Zurich (Switzerland).

The small ointment jar came from the collection of late Prof. Peter A. Kaplony, former Prof. for Egyptology in Zurich. 

The reading of the inscription immediately made it clear that this is the oldest Sothis date from ancient Egypt.

The inscription is starting from the right column is a nominal sentence with pw:


“gsw n s3-rnp.t 3bd 4 pr.t ḫft pr.t spd.t 3bd 4 3ḫt pw ḫft wp.t -rˁ”.


The sign “wp.t -rˁ” is a cow’s horn with sun disc and can be translated as ‘first day of the month’ but also as begin of the New Year, most fitting for this festival.


Translation: “Ointment made for the protection of the year, month 4, Peret-season, for the forthcoming of Sothis, month 4, Akhet-season it is, made for the first day of the month”.

The sensational discovery was published in 2015 and a new chronological model was calculated based on the new information and previously published radiocarbon dates

Rita Gautschy, Michael E. Habicht, Francesco M. Galassi, Rainer Hannig, Daniela Rutica et al. 2017. A New Astronomically Based Chronological Model for the Egyptian Old Kingdom

Journal of Egyptian History. DOI:

Take me to the article

Sothis dates:

Their pivotal importance for Chronology

The Egyptian civil calendar consisted of 365 days arranged in the three seasons Akhet, Peret and Shemu, each containing four months with 30 days and at the end, five additional days (Epagomenals) were added.


The civil calendar started with an assumed observation of the heliacal rising of Sirius (Sothis) on 1st month, Akhet, 1st day when the calendar was implemented in the 3rd Millennium BC. The heliacal rising of Sirius denotes its first visibility in the morning sky after a period of invisibility.  


Lacking any intercalary days, the Egyptian civil calendar permanently shifted one day in four years in comparison to the stars. As a result, the New Year was moving through the civil calendar: By the end of the Old Kingdom the heliacal rising of Sothis had already shifted into the Peret season.


The mentioning of a heliacal rising of Sothis combined with a date of the Egyptian calendar therefore may allow quite accurate absolute dating using astronomical charts. Only few Sothic dates are known from Ancient Egypt, the oldest complete date so far was the el-Lahun date from the 12th Dynasty. Although extremely rare, Sothis dates are of highest importance for the chronology of Ancient Egypt and ancient cultures of the Near East since the dating of the Egyptian Culture and of neighbouring regions depend on them.


New Chronology:

Recalculating the dates reported from the Old Kingdom

During the Old Kingdom, a special year count was used and the method of counting years used during Dynasties 3 to 6 is still a matter of debate. The standard theory for many years was that a regular biannual count of regnal years was employed throughout the whole Old Kingdom (Gardiner, A.H. “Regnal Years and Civil Calendar in Pharaonic Egypt”. JEA 31 (1945): 11-28.). Basic idea of this hypothesis is that after each “year of the xth cattle count” should have been followed by a “year after the xth cattle count”. It has long been noticed that the number of documents containing a “year of the count” and a “year after the count” is not about equal – the ratio amounts to approximately 2.8:1.

Based on these numbers John Nolan proposed a connection with the original lunar calendar, namely that a “year after the count” was employed if an intercalary month was inserted into the lunar calendar at the end of the preceding year in order to keep it in line with the sidereal and solar year  (J. F. Nolan Cattle, Kings and Priests: Phyle Rotations and Old Kingdom Civil Dates”. In Towards a New History for the Egyptian Old Kingdom: Perspectives on the Pyramid Age. 337-365. Leiden: Brill, 2015.)

Nolan also proposed that a regular nineteen-year intercalation cycle comparable to the much later well-known Metonic cycle has been used in ancient Egypt. The so-called original lunar calendar was tied to the heliacal rising of the star Sirius. A new lunar month began with the invisibility of the lunar crescent in the morning sky. A normal year consisted of twelve lunar months. Since such a lunar year with twelve months is about ten days shorter than a sidereal year an extra month has to be inserted after three years and at times already after two years in order to keep the lunar calendar synchronised with the sidereal year.

In our chronological study, we calculated the beginnings of lunar months and the dates of the heliacal rising of Sirius for the time span 2700 BC to 2000 BC. The first actual visibility of Sirius in the morning sky is highly dependent on the seeing conditions. An elevation of Sirius of 2° to 3° above the horizon was chosen with arcs of vision of 9° and 10° to account for excellent to fair observing conditions in the calculations. To test our hypothesis, we collected all Old Kingdom dates given in documents, inscribed on monuments or objects from the Dynasties 4 to 6 mentioning about 150 different years of Pharaohs: Some of these dates are well connected to a reign of a king or implemented in a dated architectural context and are generally accepted. Other dates are uncertain in the reading of the year or attributed to several potential reigns. Of special importance are the archives from the mortuary temples of Raneferef and Neferirkare in Abusir.

The new Sothic date from the Old Kingdom lacks the name of the King. The given date, 4th month of Akhet, day 1 allocates the vessel somewhere between 2419-2406 BCE if a reference point of Memphis is assumed. Stylistically, the jar can be attributed to the mid-5th to early 6th dynasty. The absolute date given by the Sothic date is in very good agreement with published radiocarbon determinations that locate the accession date of Djedkare Isesi to about 2450 BC and the reign of Unas to about 2420 BC.

In a second step the reigns of Djedkare Isesi and Unas were pinned down with the help of the lunar dates from the Neferirkare archive. Only then the contemporary documented year dates of Djedkare Isesi and Unas were added and the underlying hypothesis tested that a “year after” was counted if the preceding year contained 13 lunar months. For in total 28 different documented years for these two kings only one disagreement with the calculations emerged in the case of our chronological models.

Thus, while the absolute dates of Djedkare Isesi and Unas in the chronological models can be pinned down thanks to the lunar dates and a wealth of dated documents, the absolute dates and the resulting reign lengths of all other kings are less precise.


At this point I must apologize to the reader for the complicated text. In reality the study is much more complicated and the calculations took more than a year, even with the support of modern computer models and special programs. At this point I would like to express my sincere thanks to the astronomer and archaeologist Dr. Rita Gautschy - without her help the study could not have been done at all.