In Greek mythology, Theia /ˈθiːə/ (sometimes rendered Thea, Théa or Thia), also called Euryphaessa "wide-shining", is a Titaness. The name Theia alone means simply "goddess" or "divine"; Theia Euryphaessa (Θεία Εὐρυφάεσσα) brings overtones of extent (εὐρύς, eurys, "wide", root: εὐρυ-/εὐρε-) and brightness (φάος, phaos, "light", root: φαεσ-). Her brother/consort is Hyperion, a Titan and god of the sun, and together they are the parents of Helios (the Sun), Selene (the Moon), and Eos (the Dawn).
Hesiod's Theogony gives her an equally primal origin, a daughter of Gaia (Earth) and Uranus (Sky).Robert Graves also relates that later Theia is referred to as the cow-eyed Euryphaessa who gave birth to Helios in myths dating to Classical Antiquity.
Once paired in later myths with her Titan brother Hyperion as her husband, "mild-eyed Euryphaessa, the far-shining one" of the Homeric Hymn to Helios, was said to be the mother of Helios (the Sun), Selene (the Moon), and Eos (the Dawn).
Pindar praises Theia in his Fifth Isthmian ode:
Mother of the Sun, Theia of many names, for your sake men honor gold as more powerful than anything else; and through the value you bestow on them, o queen, ships contending on the sea and yoked teams of horses in swift-whirling contests become marvels.
She seems here a goddess of glittering in particular and of glory in general, but Pindar's allusion to her as "Theia of many names" is telling, since it suggests assimilation, referring not only to similar mother-of-the-sun goddesses such as Phoebe and Leto, but perhaps also to more universalizing mother-figures such as Rhea and Cybele.
Theia's mythological role as the mother of the Moon goddess Selene is alluded to in the application of the name to a hypothetical planet which, according to the giant impact hypothesis, collided with the Earth, resulting in the Moon's creation.
Theia's alternate name Euryphaessa has been adopted for a species of Australian leafhoppers Dayus euryphaessa (Kirkaldy, 1907).