  The Ancient Egyptians wrote Calendars of Lucky and Unlucky Days that assigned
astronomically influenced prognoses for each day of the year. The best
preserved of these calendars is the Cairo Calendar (hereafter CC) dated to
1244--1163 B.C. We have presented evidence that the 2.85 days period in the
lucky prognoses of CC is equal to that of the eclipsing binary Algol during
this historical era. We wanted to find out the vocabulary that represents Algol
in the mythological texts of CC. Here we show that Algol was represented as
Horus and thus signified both divinity and kingship. The texts describing the
actions of Horus are consistent with the course of events witnessed by any
naked eye observer of Algol. These descriptions support our claim that CC is
the oldest preserved historical document of the discovery of a variable star.
The period of the Moon, 29.6 days, has also been discovered in CC. We show that
the actions of Seth were connected to this period, which also strongly
regulated the times described as lucky for Heaven and for Earth. Now, for the
first time, periodicity is discovered in the descriptions of the days in CC.
Unlike many previous attempts to uncover the reasoning behind the myths of
individual days, we discover the actual rules in the appearance and behaviour
of deities during the whole year.
