Nyx in Hesiod
In Hesiod's Theogony, Night is born of Chaos; her offspring are many, and telling. With her brother Erebus, Night gives birth to Aether ("atmosphere") and Hemera ("day"). Later, on her own, Night gives birth to Momus "blame", Ponos "toil", Moros "fate", Thanatos "death", Hypnos "sleep", "the tribe of dreams", the Hesperides, the Keres and Fates, Nemesis, Apate "deception", Philotes "friendship", Geras "age", and Eris "strife",
In his description of Tartarus, Hesiod says further that Hemera "day", who is now Night's sister rather than daughter, left Tartarus just as Nyx entered it; when Hemera returned, Nyx left. This mirrors the portrayal of Ratri "night" in the Rig-Veda, where she works in close cooperation but also tension with her sister Ushas "dawn".
Nyx (or also possible Clotho) from the Pergamon Zeus Altar
Nyx in Orphic Poetry
Night took on an even more important role in several fragmentary poems attributed to Orpheus. In them, Night, rather than Chaos, is the first principle. Night occupies a cave or adyton, in which she gives oracles. Kronos - who is chained within, asleep and drunk on honey - dreams and prophesies. Outside the cave, Adrastea clashes cymbals and beats upon her tympanon, moving the entire universe in an ecstatic dance to the rhythm of Nyx's chanting.
Other Greek texts
Night is also the first principle in the opening chorus of Aristophanes's Birds, which may be Orphic in inspiration. Here she is also the mother of Eros. In other texts she may be the mother of Charon (with Erebus), and Phthonus "envy" (with Dionysus?).
The theme of Night's cave or house, 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 Night; this hypothesis, however, must remain tentative.
Cults of Night
In Greece, Night is only rarely the recipient of cult. According to Pausanias, she had an oracle on the acropolis at Megara (Paus. 1.40.1).
More often, Nyx lurks in the background of other cults. Thus there was a statue called Night in the temple of Artemis at Ephesus. The Spartans had a cult of Sleep and Death, conceived of as twins (Paus. 3.18.1) - no doubt with Night as their mother. Cult titles composed of compounds of nyx- are attested for several gods, most notably Dionysus Nyktelios "nocturnal" (Paus. 1.40.6) and Aphrodite Philopannyx "who loves the whole night" (Orphic Hymn 55).
Nyx outside of Greece
In Roman texts that takes up this Greek theme, Nyx is translated as Nox. (Virgil V, 721)