In ancient Egypt, the goddess Nut was the mother of gods. She was the night sky; and the Milky Way in particular. Alternatively, her body can be interpreted as the path of the stars, and she might even have been one specific constellation. Naked, in her full feminine beauty, she was bending over the Earth with her two hands and feet touching the North, East, South and West. Sometimes, she was a sky cow decorated with stars and carried the Sun god, Ra, into the heavens.
When they died, the Egyptians embellished the lid of their coffins with her image, and asked her to spread herself over them and put them among the stars in the night sky. She was the womb where they returned to be born again, just like the Sun, who set in Nut’s mouth every evening and emerged every morning through her birth canal.
The goddess of the night sky does resemble a lot the dea abscondita of the alchemists, or her Christianised version, the Black Madonna. All give form to the light that exists within the darkness. To consciousness, which emerges and returns to the unconscious following a certain rhythm or cycles.
According to The Oxford Encyclopedia of Ancient Egypt, it was around 4500 B.C. that the Ancient Egyptians defined the year as consisting of 365 days. That includes the twelve times thirty days of each month and five extra days at the end of the year. In the coffin texts, Nut is described as the mother of those five additional (epagomenal) days. According to Plutarch, she was cursed by the Sun god not to be able to have children any time during the year, but Thoth (Mercurius) won a game and demanded five extra days to the calendar as his victory. This was the timespan when Nut could conceive and give birth. 
In that era, exactly at the time of the winter solstice, the Sun was observed to descend in the constellation of Gemini, the mouth of Nut (ruled by Mercury according to astrological symbolism). Six thousand years later, in sixteenth-century alchemical texts, the philosophers’ stone was still created in the vessel of Mercurius/Hermes, also called a “virginal womb” or “Mary’s womb”.
“So below, so above” says the Tabula Smaragdina of Hermes Trismegistus. Or, as Schopenhauer puts it: “Thus everyone in this twofold regard is the whole world itself, the microcosm; he finds its two sides whole and complete within himself. And what he thus recognizes as his own inner being also exhausts the inner being of the whole world, of the macrocosm”.
For the ancient Egyptians, the cycle of light and darkness was not a mechanism, it was a dynamics. The former is the endless repetition of the same. The latter is an ever-changing system that goes through certain predictable phases or cycles. It is the journey of the Sun god, Ra, through the body of Nut. The Sun rises. The Sun sets. Is it the same day that starts all over again, every morning? Yes and no. Are we the same person as we were twenty years ago? Yes and no.
What is it that stays itself no matter how much it changes? What is it that is never exactly the same no matter how identical it seems? Whatever it is, it belongs in the body of Nut, in the womb of the Virgin. After it enters the darkness and before it emerges into the light, it is embraced and nurtured by the goddess. And it will always be itself and it will never be the same, just like She, Herself.
 Geraldine Pinch, Egyptian Myth: A Very Short Introduction (Oxford: Oxford University Press, 2004), 174.
 Ian Shaw & Paul T. Shaw, The British Museum Dictionary of Ancient Egypt (Cairo: The American University in Cairo Press, 1997), 207.
 George Hart, The Routledge Dictionary of Egyptian Gods and Goddesses (London: Routledge, 2005), 110.
 Geraldine Pinch, Handbook of Egyptian Mythology (Santa Barbara: ABC-CLIO, 2002), 174.
 Ian Shaw & Paul T. Shaw, The British Museum Dictionary of Ancient Egypt (Cairo: The American University in Cairo Press, 1997), 42.
 Donald B. Redford, The Oxford Encyclopedia of Ancient Egypt, Vol 2 (Oxford: Oxford University Press, 2001) 145-6.
 Geraldine Pinch, Handbook of Egyptian Mythology (Santa Barbara: ABC-CLIO, 2002),174.
 Donald B. Redford, The Oxford Encyclopedia of Ancient Egypt, Vol 2 (Oxford: Oxford University Press, 2001), 146.
 Joseph Campbell, The Masks of God Vol. 4. (New York: Penguin Books, 1991), 272-3.
 Arthur Schopenhauer, The World as Will and Representation, Vol 1 (New York: Dover Publications, 1969), §29.