Nyx is the Greek goddess of the night. A shadowy figure, Nyx stood at or near the beginning of creation, and mothered other personified deities such as Hypnos (Sleep) and Thanatos (Death), with Erebus. Her appearances are sparse in surviving mythology, but reveal her as a figure of such exceptional power and beauty, that she is feared by Zeus himself. She is found in the shadows of the world and only ever seen in glimpses.
In Hesiod's Theogony, Nyx is born of Chaos. With Erebus (Darkness), Nyx gives birth to Aether (Brightness) and Hemera (Day). Later, on her own, Nyx gives birth to Moros (Doom, Destiny), Ker (Fate, Destruction, Death), Thanatos (Death), Hypnos (Sleep), the Oneiroi (Dreams), Momus (Blame), Oizys (Woe, Pain, Distress), the Hesperides (Evening, Sunset), the Moirai (Fates), the Keres, Nemesis (Indignation, Retribution, heavenly punishment for excessive hybris), Apate (Deceit), Philotes (Friendship, Love), Geras (Old Age), and Eris (Strife).
In his description of Tartarus, Hesiod locates there the home of Nyx, and the homes of her children Hypnos and Thanatos. Hemera (Day), who is Nyx's daughter, left Tartarus just as Nyx entered it; continuing cyclicly, when Hemera returned, Nyx left. This mirrors the portrayal of Ratri (night) in the Rigveda, where she works in close cooperation but also tension with her sister Ushas (dawn).
At Iliad 14.249–61, Hypnos, the minor deity of sleep, reminds Hera of an old favor after she asks him to put Zeus to sleep. He had once before put Zeus to sleep at the bidding of Hera, allowing her to cause Heracles (who was returning by sea from Laomedon's Troy) great misfortune. Zeus was furious and would have smitten Hypnos into the sea if he had not fled to Nyx, his mother, in fear. Homer goes on to say that Zeus, fearing to anger Nyx, held his fury at bay and in this way Hypnos escaped the wrath of Zeus by appealing to his powerful mother. He disturbed Zeus only a few times after that always fearing Zeus and running back to his mother, Nyx, who would have confronted Zeus with a maternal fury.
Nyx took on an even more important role in several fragmentary poems attributed to Orpheus. In them, Nyx, rather than Chaos, is the first principle from which all creation emerges. Nyx occupies a cave or adyton, in which she gives oracles. Cronus – who is chained within, asleep and drunk on honey – dreams and prophesies. Outside the cave, Adrasteia clashes cymbals and beats upon her tympanon, moving the entire universe in an ecstatic dance to the rhythm of Nyx's chanting. Phanes – the strange, monstrous, hermaphrodite Orphic demiurge – was the child or father of Nyx. Nyx is also the first principle in the opening chorus of Aristophanes' The Birds, which may be Orphic in inspiration. Here she is also the mother of Eros.
The theme of Nyx's cave or mansion, beyond the ocean (as in Hesiod) or somewhere at the edge of the cosmos (as in later Orphism) may be echoed in the philosophical poem of Parmenides. The classical scholar Walter Burkert has speculated that the house of the goddess to which the philosopher is transported is the palace of Nyx; this hypothesis, however, must remain tentative.
In 1997, the International Astronomical Union approved the name Nyx for a mons (mountain/peak) feature on the planet Venus. Nyx Mons is located at latitude 30° North and longitude 48.5° East on the Venusian surface. Its diameter is 875 km.
On June 21, 2006, the International Astronomical Union renamed one of Pluto's recently discovered moons (S/2005 P 2) to Nix, in honor of Nyx. The name was spelled with an "i" instead of a "y", to avoid conflict with the asteroid 3908 Nyx