AstroEgypto

For nearly two centuries, archaeologists have been discovering new monuments,
bringing to light ancient texts that philologists are working to decipher.
Most of these vestiges attest a certain interest of the Egyptian people
in the sky, the objects which make it up, the movements which drive them.
With the help of modern tools, let's discover them in an animated light!

Introduction

Numerical simulations can be used to quickly and easily visualize a number of archaeoastronomical problems: the orientation of monuments, the succession of star risings and settings on the surface of the local horizon, the culmination of stars in the local meridian, etc. The ensuing simulations were carried out using the three Culture Diff' software packages designed during my doctoral thesis, as well as a brand-new, 5D Sky/Earth interface: three dimensions represent the surface of our planet - in other words, the relief; the stars visible to the naked eye are grouped together on the surface of a sphere, the celestial sphere; finally, time (past, present and future) makes up the fifth dimension. Thanks to this Sky/Earth interface, it is now possible to move on the surface of our Earth, at the foot of the Egyptian pyramids for example, and to visualize the celestial vault as it was at the time of their construction.

The astronomical orientation of the Old Kingdom pyramids

Hereafter, the problematics of the astronomical orientation of the pyramids of Egypt is summarized in three short video sequences, made up from numerical simulations. This question was the subject of a book published in 1998 and of an scientific paper published in the Cahiers Caribéens d'Egyptologie n°15 (2011).

Sunset on the Giza pyramids in the year 2500 BC

The three pyramids of Giza, erected under the reigns of the pharaohs Cheops, Khafre and Mycerinus between the years 2550 and 2500 BC, are perfectly aligned in the direction of the cardinal points - as shown in this animation depicting the setting of the Sun behind the pyramid of Khafre on the day of the spring equinox. To achieve such a result, did Pharaoh's architects observe the rising or setting positions of a star, of the Sun? Or the upper culmination, in the northern sky, of one or more circumpolar stars? Did they use one or several instruments of observation and projection on the ground? These are the questions which have been posed to the Egyptologists and the Astronomers for several decades...

Heliacal setting of Procyon on the plateau of Giza in 2500 BC

The deviations from the east-west alignment could be measured on eleven pyramids of the Old Kingdom: those of the pharaohs Djoser, Huni, Snefru (2), Cheops, Djedefre, Chephren, Mykerinus, Sahure, Neferirkare and Unas. The insertion of these archaeological data within a numerical model allowing to recreate the conditions of observation of the celestial vault at the places and historical periods considered, has highlighted the possibility that the repeated observation, over more than 500 years, of the setting position (in the night or twilight sky) of one particularly bright star, alpha Canis Minoris (Procyon), could account for the orientation of each of the eleven pyramids of the Old Kingdom. The animation on the left shows the heliacal setting of Procyon in the axis of the pyramid of Chephren in 2500 BC.

The « Stretching of the Cord » ceremony

At the historical period considered, the heliacal setting of the star alpha Canis Minoris - that is to say, its disappearance in the western sky in the glow of the setting Sun - coincided with the upper culmination, in the northern sky, of the star eta Ursae Majoris materializing the extremity of the constellation of the Big Dipper - on the animation on the right, this star is circled in red. This conjunction evokes the content of texts describing the course of the Stretching of the Cord ceremony, of which several extracts have been found among the remains of monuments dating from the Old Kingdom to the Ptolemaic Period - a sign of the antiquity and persistence of this ritual preceding the laying of any foundation stone...