Plutarch, in his essay on Isis and Osiris, mentions an Egyptian festival that he says marked the beginning of spring and which was called The Entry of Osiris into the Moon. Here’s what he says:
Further, on the first day of the month of Phamenoth they hold a festival, which they call Entry of Osiris into the Moon, for it is the beginning of spring. Thus they locate the power of Osiris in the moon and say that Isis, as the creative principle, has intercourse with him. For this reason they also call the moon the mother of the world and they believe her nature to be both male and female since she is filled and made pregnant by the sun while she herself in turn projects and disseminates procreative elements in the air. (Plutarch, On Isis and Osiris, 43)
In his discussion of this passage, J. Gwyn Griffiths (have I mentioned he’s one of my favorite Egyptologists?) notes that there is no festival by that name in any known Egyptian calendar. Yet there are Egyptian texts from the temple at Denderah that show Osiris in a boat with Isis and Nephthys and explain that Osiris is entering into the Left Eye; and the Left Eye, as you may know, is an Egyptian designation for the moon. In the Denderah texts, spring is not mentioned, but Osiris is said to do His entering on the 15th of the month, that is, at the full moon. So in these texts, Osiris is seen as the sun as He enters into and unites with the full moon.
This also seems to be the case in what Plutarch writes. Osiris enters into the moon and Isis, the Creative Principle, unites with Him in sexual intercourse. Like the moon—the Mother of the World—Isis is filled and made pregnant by the sun, which has to be identified with Osiris. The moon is then both male and female for Isis and Osiris are united in it.
To date, this is all I know about this ever-so-intriguing reference. But I very much like the idea of a spring sexual rite of Isis and Osiris and, in fact, this reference inspired the rite of sacred sexuality in Isis Magic. A rite of sacred sexuality makes a great deal of sense as a rite of spring—when everything else is waking up and having sex and getting fertile once again. Bunnies. Eggs. Flowers waving their genitalia in the spring air. You get it.
In another part of his essay, Plutarch mentions an Egyptian tradition that the confinement of Isis (while She is pregnant with Horus and awaiting His birth) was celebrated after the spring equinox. This actually could work if Isis becomes pregnant at the spring equinox and carries Horus until His birth at the winter solstice, a period of nine months—or by Egyptian lunar count, ten. One of the Isis aretalogies notes that Isis decreed that women should give birth in the tenth month.
I’m not quite sure how to place the death of Osiris in this scheme, for His death rites are generally celebrated after the autumnal equinox. In that case, He has approximately six months in the otherworld, which is perhaps sufficient time for Isis to use Her magic to raise Him so that, by the vernal equinox, He can “enter into the moon,” make love with Her, and beget Their Holy Child.
Just to be clear, no Egyptian tradition that I know of includes this particular seasonal timetable, yet I think it’s a fair conjecture and should be more than enough to inspire the appropriate rites of spring in Her devotees. Happy spring equinox…and may Isis and Osiris inspire and bless you in this season of growing light and life.