Isidora Forrest has a post about the rites of spring for Isis. It also mentions the Festival: Entry of Osiris into the Moon (from Plutarch).
As she mentions, for the ancient Egyptians, Wesir was a lunar deity and the phases of the moon was analogous to the death and renewal of Wesir. So maybe, another way to look at this festival would be for Aset (as the Creative principle as the solar goddess here; Aset was a solar Goddess for the ancient Egyptians) and Wesir being already whole is renewed via Aset’s solar rays: as moonlight is sunlight reflected back.
Fiercely Bright One 