Medhat told us about one of the Old Kingdom's major celebrations, Carnival and Easter of the ancients so to speak: The Opet Festival.
This festival was a reenactment of the regeneration of Amun-Re with Mut and Khonsu. It began usually in the second month of the Egyptian calendar, Akhet II after the Nile flooded the river banks. Once the waters rose, the priests would have pronounced that festivities were to begin. The celebration and feast lasted for several days: Medhat quoted 21 days. Since the flooding prevented any field work, the people had time to party and they did as the reliefs vividly show.
The religious part of the ceremony began in the sanctuary of Amun-Re at Karnak where a statue of the god was carried on a model ship by the priesthood from the Akhet-Menu behind the sacrificial altar towards the center of the Karnak temple and then southwestwards towards the Temple of Luxor. Recall that the Karnak Temple is oriented north-west to south-east. Thanks to Medhat we learned that this orientation aimed for the winter solstice when the sun reaches its south-most position on the horizon both at sunrise and sunset. Symbolically, this marked the end of the sun's journey as if dying only to reverse course and relive after a period of three days.
On the way from Karnak to Luxor, similar statues on model ships joined the procession from the temples of Mut and Khonsu and so did the reigning king himself and his entourage. The king just like the gods of the Theban Triad were being re-coronated each year with the Opet Festival which affirmed his authority and divine legitimacy in the eyes of the both the gods and the people. The regeneration of the gods and re-coronation of the king would have occurred in the sanctuary of the Luxor temple at the southwest extreme of the entire complex where the sun set in the evening and where the procession reached its ceremonial end and Opet concluded.
There is a loose end to this which I have not resolved. The Opet Festival was celebrated in the summer when the Nile flooded, but the orientation of the Karnak and Luxor Temples suggests a winter solstice theme. How can this be explained?
I think the answer is that the axis was actually oriented towards two celestial events which happened to locate to the same position from the vantage point of Thebes....and this may actually have been why Thebes was selected as the new capital of Egypt after the Middle Kingdom. I will have to double-check this with astronomic software to see if the star Sirius also reappeared on the horizon in the same position as the sun on the winter solstice only in the summer during the time of the Nile's flooding at which time the Opet Festival was celebrated. Update to follow.