In the second civil month, the great New Kingdom celebration of Opet predominated. It was a rite expressly connected with the pharaoh and his father Amun(-Re). This extensive festival, also set by the moon, saw the pharaoh-to-be traveling to the temple of Luxor at Thebes in order for his father Amun to give him the powers of kingship as the living Horus falcon. By the New Kingdom, the intimate connection between Amun and pharaoh was solidified in official state religion by this festival, and its twenty-seven-day duration in the twentieth dynasty indicates how significant it had become.
– The Ancient Gods Speak: A Guide to Egyptian Religion, Donald B. Redford, editor.