Who was the primordial goddess of the day in Greek myth?

The primordial goddess of the day in Greek myth was Hemera. She personified daylight itself, standing as the cosmic counterpart to Nyx, the personification of night.

According to Hesiod’s Theogony, Hemera was born from Erebus, or Darkness, and Nyx, or Night. Her brother was Aether, the bright upper air. This genealogy belongs to the earliest generation of cosmic powers, before the Titans and Olympians dominate Greek myth.

Hemera was not exactly the same figure as Eos, the goddess of dawn. Eos represents the arrival of morning, while Hemera embodies day as a whole. Ancient and later writers sometimes identified or blended the two, which can make simplified family trees appear inconsistent.

Other traditions give Hemera a different parentage, including an account linking her to Chronus and Nyx. Those variations reflect the diversity of Greek myth, but Hemera remains the standard answer for the primordial personification of day.