Ushas (Marici for Buddhists) is the goddess of the dawn. What are the passages in the vedas where she is mentioned exactly?
Like many epithets ( Indra, Vishnu, etc) referring to various aspects of the Almighty God, Ushas (Dawn) is an epithet used in Rig Veda to indicate emerging of REALISATION/WISDOM.
Many hymns were dedicated to Ushas in Rig Veda. Forty of its hymns are dedicated to her, while her name appears in other additional hymns.
and so on.