The Decans and the Ancient Egyptian Skylore: an Astronomical Approach

Juan Antonio Belmonte

Instituto de Astrofisica de Canarias


"To attempt to go further in the determination of the decans is not only of very little
interest but would necessarily imply ascribing to our texts an astronomical accuracy which they were never intended to have" O. Neugebauer (The Exact Sciences in Antiquity, 1957). This over pessimistic sentence was written more than four decades ago by one of the most important historians of ancient astronomy so far. Despite his merits in the field, statements like this have severely handicapped any advance in ancient Egyptian skylore specially when focused from an actual astronomical point of view. It is the intention of this work to convince scholars and the general publicthat we not only can go further but also that we must do it.

This work deals with the ancient Egyptian decans and constellations of various epochs since the Star Clocks painted inside the coffins of the 1st Intermediate period (c. 2100 BC) until the monumental "zodiacs" of the Ptolemaic temples including the marvellous representations on the ceilings of the New Kingdom tombs. We have studied these marvellous works of art interdisciplinary from the artistic, symbolic, linguistic and astronomical point of view, reaching interesting discoveries and conclusions.

For example, we propose sensible translations for most of the decans and speculate with the translation of the most difficult terms. Also, inspired by Kurt Locher's claim about the identification of Sah, we propose that originally Spd (later Spdt) was not a single star (Sirius) but rather an asterism represented in some coffins that can be easily recognized in the Heavens. Beside, we propose, following V.L. Davis that the Milky Way would have been the frontier between the northern and the southern skies of ancient Egypt, mentioned in the hieroglyphic texts, simplifying the process of identification.

We have used the Gotto Planetarium of the Science and Cosmos Museum in Tenerife and several computer programs to perform the astronomical approach to the problem. Stars and asterisms rising in ten day intervals were first selected and later the dates of their heliacal risings verified for several epochs and latitudes.

As a matter of fact, we believe that several decans can be identified with a certain degree of confidence and for others good omens can be proposed. From our results, we might even propose that Egyptian skylore, referenced for the first time in written sources in the Pyramid Texts (c. 2350), inspired the creation of the decanal system somewhere in the Middle Egypt around the year 2200 BC, perhaps during the poorly known period of rule of the Heracleopolitan dynasties.