Nut was the sky — the great vault above the world, painted blue and powdered with stars, beneath whose body the sun and the moon performed their daily and monthly courses. She was the daughter of Shu and Tefnut, the sister and wife of Geb the earth, and the mother of Osiris, Isis, Set, and Nephthys. She was depicted in the standard Egyptian iconography arched over the body of Geb, supported by the upraised hands of her father Shu; her elongated body bore the constellations along its length, and her mouth, at the western horizon, swallowed the sun each evening. In the night, the sun traveled through her body; in the morning, she gave birth to him at the eastern horizon, and the sky became red with the blood of her labor.

There is a tale, much elaborated in the late temple texts, of how Nut was forbidden by her father Ra to bear children in any month of the year; for it had been prophesied that her offspring would inherit the kingship from him, and he sought to prevent the birth. But Thoth the wise played at draughts with the moon and won from him five days of light, which were not part of any month — the five "epagomenal" days that the Egyptian calendar adds to the twelve thirty-day months — and on each of these days Nut bore a child. So Osiris was born on the first, Horus the Elder on the second, Set on the third, Isis on the fourth, and Nephthys on the fifth; and the prophecy was fulfilled.