Aah is the ancient Egyptian god of the moon. His names translate into the Egyptian word of the moon. Alternative spellings of his name include Iah, Aa, Ah, Aos, Yah, Aah Tehuti or Aah Te-huti that may also mean “collar”, “defender” or “to embrace”. He is associated with other lunar deities including Thoth and Khonsu who may have eclipsed his popularity. He is sometimes believed to be the adult form of the child moon god Khonsu who eventually assimilated his functions. He is also believed to be the student of the god of wisdom, Thoth who likewise absorbed some of his functions. However, despite his waning following over the course of Egyptian history, Aah remains to be a fixture in Egyptian amulets and hieroglyphs.
He is often represented as a man with a tight fitting garment wearing a crown made of a sun disk with a crescent moon on top of it. Sometimes, he is seen wearing the Atef crown topped by moon resting on a full, long, tripartite wig. He may also be seen carrying a long staff.
His existence was further proven when he was mentioned in the Book of the Dead saying, “I am the moon-god Aah, the dweller among the gods”.
Aah is credited for having created the original Egyptian calendar. The said calendar is divided into 12 months with 30 days every month. In one of the myths, Nut, the sky and Geb, the earth were siblings, who were locked in what seemed like an eternal embrace. Their almost unbreakable bond irked their father, the sun god Ra, who abhorred their incestuous relationship. He cursed them that will never bear children on any day of the year when they continued their relationship despite his disapproval. Nut and Geb sought refuge in Thoth, the god of wisdom and knowledge. Thoth devised a plan to gamble with the creator of the calendar, Aah. The wager was that Aah would give Thoth five days of his moonlight if he won. Thoth won and the five days became the extra five days of the year. Nut was able to bear children on each day because it was not covered by the curse of Ra. She gave birth to Osiris, Isis, Set, Nephthys and Horus the elder on each day. These days were believed to be inserted in the month of July making all of them July babies.
As cited from EgyptianGods.Org