“In magical papyri we are often told not to perform certain magical ceremonies on such and such days, the idea being that on these days hostile powers will make them to be powerless, and that gods mightier than those to which the petitioner would appeal will be in the ascendant.
There have come down to us, fortunately, papyri containing copies of the Egyptian calendar, in which each third of every day for three hundred and sixty days of the year is marked lucky or unlucky, and we know from other papyri why certain days were lucky or unlucky, and why others were only partly so (see Brit. Mus. Papyrus, No. 10,474).
Taking the month Thoth, which was the first month of the Egyptian year, and began, according to the Gregorian Calendar, on August 29th, we find that the days are marked as follows:—
Now the sign means “lucky,” and means “unlucky”; thus at a glance it could be seen which third of the day is lucky or unlucky, and the man who consulted the calendar would, of course, act accordingly.
It must be noted that the priests or magicians who drew up the calendar had good reasons for their classification of the days, as we may see from the following example. The 19th day of Thoth is, in the above list, marked wholly lucky, i.e., each third of it is lucky, and the papyrus Sallier IV (see Chabas, Le Calendrier, p. 24) also marks it wholly lucky, and adds the reason:—
“It is a day of festival in heaven and upon earth in the presence of Râ. It is the day when flame was hurled upon those who followed the boat containing the shrine of the gods; and on this day the gods gave praises being content,” etc.
But in both lists the 26th day is marked wholly unlucky, the reason being, “This was the day of the fight between Horus and Set.” They first fought in the form of men, then they took the form of bears, and in this state did battle with each other for three days and three nights.
Isis aided Set when he was getting the worst in the fight, and Horus thereupon cut off his mother’s head, which Thoth transformed by his words of power into that of a cow and put on her body. On this day offerings are to be made to Osiris and Thoth, but work of any kind is absolutely forbidden.”
E.A. Wallis Budge, Egyptian Magic, London, 1901. Pp. 224-6.