Cambridge Archaeological Journal

Research Article

Evidence of Periodicity in Ancient Egyptian Calendars of Lucky and Unlucky Days

Sebastian Porceddua1, Lauri Jetsua2, Tapio Markkanena3 and Jaana Toivari-Viitalaa4

a1 Oritmurrontie 46, 04430 Järvenpää, Finland; Email:

a2 Observatory, P.O. Box 14, 00014 University of Helsinki, Finland; E-mail:

a3 Observatory, P.O. Box 14, 00014 University of Helsinki, Finland; E-mail:

a4 Institute for Asian and African Studies, P.O. Box 59 (Unioninkatu 38B), 00014 University of Helsinki, Finland; E-mail:


This article presents an experiment in time series analysis, specifically the Rayleigh Test, applied to the ancient Egyptian calendars of lucky and unlucky days recorded in papyri P. Cairo 86637, P. BM 10474 and P. Sallier IV. The Rayleigh Test is used to determine whether the lucky and unlucky days are distributed randomly within the year, or whether they exhibit periodicity. The results of the analysis show beyond doubt that some of the lucky days were distributed according to a lunar calendar. The cycles of the moon thus played an important role in the religious thinking of the Egyptians. Other periods found using the Rayleigh Test are connected to the civil calendar, the mythological symbolism of the twelfth hour of the day and possibly the period of variation of the star Algol.

Sebastian Porceddu is a graduate student of Astronomy at the University of Helsinki since 2007. In the same year he also received a Master's degree in Egyptology. He is currently working on his doctoral dissertation which concerns the application of time series analysis to various topics of interest, for example the terrestrial impact crater record and ancient Egyptian calendars.

Lauri Jetsu has been the director of the Observatory of University of Helsinki since January 2001. His main research intrest has been time series analysis of different types of data, such as solar and stellar magnetic-activity indicators or the terrestrial impact crater record.

Tapio Markkanen is a Professor at the University of Helsinki. He teaches astronomy and history of science and has done research especially on galactic structure, magnetic fields, and star formation. He has also published scholarly works on the history of science.

Jaana Toivari-Viitala is an Associate Professor of Egyptology (Docent) and Head of Egyptology at the University of Helsinki. She received her doctorate at the University of Leiden in 2000, and is at present Head of the research project ‘Personal Names at Deir el-Medina’.