The Greek Titaness who was the mother of the sun, moon, and dawn was Theia. In the traditional genealogy, Theia was a daughter of Gaia, the Earth, and Uranus, the sky. She became the sister-wife of Hyperion, and their children were Helios, the Sun; Selene, the Moon; and Eos, the Dawn.
Theia’s own name is linked with divinity, while her alternative name Euryphaessa means “wide-shining” or “far-brightening.” These names reflect her association with sight, brilliance, and the radiance of the heavens. Unlike many better-known Greek deities, Theia has relatively few independent myths and is chiefly remembered through her powerful family connections.
Theia can be confused with other maternal goddesses, especially Rhea, who was the mother of major Olympians such as Zeus, Hera, Poseidon, and Demeter. Phoebe was also a Titaness, but she was associated with prophecy and was the grandmother of Apollo and Artemis, not the mother of the three celestial figures named in the question.