Conception d'un modèle de visibilité d'étoile à l'oeil nu. Application à l'identification des décans égyptiens
Abstract : On the interior lid of sarcophagi, on the external surface of water clocks, on the ceiling of temples and tombs dating from about 2100 to about 50 BC and located all along the Nile river, between Alexandria and Aswân, were drawn twenty stellar clocks and eighty star lists in the order of their successive heliacal risings, nocturnal risings or transits. Their identification to stars visible with the naked eye of the Hipparcos catalogue first required the making up of a complete list of these ninety stars accompanied with the translation of their respective hieroglyphic names. The comparison between the stellar arrangements characterizing the one hundred star lists led to their grouping into six types of star lists and to the determination of the spatial, temporal and optical sighting conditions of the decanal stars. These constraints have next been applied to a visibility model of stars visible with the naked eye in the dark or twilight sky of ancient Egypt which combines several astrometric and photometric parameters. Next, the making up of star lists in the order of their heliacal risings, of their nocturnal risings or transits, the comparison with the six prototypes of star lists, the taking into account of several astronomical, philological and parietal criteria, led to contract the number of candidate stars to everyone of the ninety decanal stars. This research work led to draw a map of the sky of ancient Egypt, to better define the ancient Egyptian nighthours, to refine the beginning of the reign of several pharaohs, etc.