Doctoral thesis: Periodicity of an Ancient Egyptian hemerological calendar and terrestrial impact craters

While converting the days of an Ancient Egyptian calendar to match our contemporary calendar is not entirely straightforward, 24 November appears to be an auspicious day in the Cairo Calendar. That is also the day when Sebastian Porceddu’s doctoral thesis in physics, which combines mathematics and Egyptology, is examined at the Faculty of Science.

Sebastian Porceddu utilised in his doctoral thesis the Rayleigh test, a mathematical method used to study time point series. In the study, the dates included in Ancient Egyptian Calendars of Lucky and Unlucky Days, also known as hemerologies, were used as time points whose periodicity was investigated.

“The study shows that ancient observations can still be useful in modern astrophysics and that they can be used as points of observation, even if they no longer constitute exact measurements according to our standards,” Porceddu explains. 

Ancient Egyptian Calendars of Lucky and Unlucky Days are texts where the morning, noon and evening of a given day are given the prognosis of either ‘good’ or ‘bad’, and the texts also provide instructions for the day.

Statistical observations demonstrated that phases of the Moon influenced the good and bad days recorded in the Ancient Egyptian calendar. Furthermore, the prognoses associated with good days also describe the variation in brightness of the star Algol.

“It is entirely possible that the change in the brightness of Algol has been recorded in mythologised form in the hemerological texts. The stories concerning the god Horus in particular appear to have a connection to celestial bodies associated with visual changes, such as the Moon and Algol,” Porceddu says.

That the variation of Algol’s brightness has remained almost unchanged from the time of Ancient Egypt to today indicates, among other things, that the three stars in the Algol system are all on the same orbital plane. In addition, the mass transfer speed from Algol B to Algol A can be calculated on the basis of observations made by Ancient Egyptians.

In another application of the Rayleigh test, the doctoral thesis explores the age distribution of terrestrial impact craters.

It has been said that periodicities that indicate impacts having occurred at regular intervals can be detected in the age of the craters. In the thesis, time point series were created for randomly selected impacts and impacts occurring at regular intervals. By testing these time point series, it was found that no periodicity could be observed in the dataset, although partial regularity was found in the timing of the impacts.

While mixing digital solutions with archaeological data is currently trendy, Porceddu ran into a number of prejudices over the course of his thesis project.

The articles included in the doctoral thesis have been published over several years. Publishing on a multidisciplinary topic proved to be laborious, as it did not fall under the core field of any single publication forum.

“My articles have elicited discussion, but no one has been able to disprove the arguments in them,” Porceddu says.

Porceddu has previously completed two master’s degrees, one in astronomy and another in Egyptology, after which he embarked on his doctoral thesis alongside his day job as a specialist at the University of Helsinki’s IT Centre.

Sebastian Porceddu, MSc, defended his doctoral thesis entitled ‘Rayleigh test and astronomical time point series: from Ancient Egyptian hemerologies to terrestrial impact craters’ on 24 November 2020 at 12.00 at the Faculty of Science, University Helsinki.

Docent Hannu Karttunen from the University of Turku will serve as the opponent and Professor Karri Muinonen as the custos.

The doctoral thesis will be published in the Report series in astronomy.

The thesis ‘Rayleigh test and astronomical time point series: from Ancient Egyptian hemerologies to terrestrial impact craters’ is also available as an electronic publication.