Hemera, in Greek mythology, is the personification of day and one of the Greek primordial deities. She is the daughter of Erebus (personification of darkness) and Nyx (personification of the night). Hemera is known to have a brother named Aether, who is the personification of the upper air or light.

In the ancient cosmogonies, Night and Day are considered as independent entities where Night and Darkness (Erebus) are in one region (considered the underworld or Tartarus), while Day and Light (Hemera and Aether) are in the other region, considered as the upper world or the sky. They intermingle when Hemera exits Tartarus and travels to the upper world, signifying day, and she then goes back to Tartarus, signifying night.

Despite this role in the ancient cosmogonies, Hemera is not a widely characterized figure in Greek mythology. Her function and attributes are often assimilated with other deities, like Eos, the goddess of dawn. Hemera’s main mythological role is as the embodiment of day, signifying the cycle of day and night.