Hemera

"Then Nyx, somehow all by herself, had a daughter named Hemera, who was Day. Those two never got along because they were as different as . . . well, you know."

- Percy Jackson

Hemera is the Protogenos of the Day, daughter of Erebos and Nyx. She is the female counterpart of her brother and consort, Aether (Light), with whom she had one child: Thalassa, a Protogenos of the Sea. Her Roman aspect is Dies.

Percy Jackson's Greek Gods
In the evening Hemera's mother Nyx drew a veil of darkness between the shining atmosphere of Aether and the lower air of earth (Chaos) bringing night to man. With each morn Hemera dispersed night's mists, bathing the earth again in the shining light of heaven (Aether). In the ancient cosmogonies night and day were substances distinct and quite independent from the sun.

Hemera was closely identified with Hera, the Queen of Olympus, and Eos, goddess of the dawn. Hesiod appears to regard her as more of a divine substance rather than anthropomorphic goddess. She was largely irrelevant in mythology, with her role being wholly subsumed by the goddess Eos.

Pausanias seems to confuse her with Eos when saying that she carried Cephalus away. Pausanias makes this identification with Eos upon looking at the tiling of the royal portico in Athens, where the myth of Eos and Kephalos is illustrated. He makes this identification again at Amyklai and at Olympia, upon looking at statues and illustrations where Eos (Hemera) is present.

The House of Hades
When confronting Nyx, Percy Jackson and Annabeth Chase pretended to be tourists, unimpressed by the Primordial of Night. But they added that Hemera might be more interesting. Offended, Nyx snapped that Hemera (Day) was her daughter, and that Night was much more impressive than Day.

Appearance
In Percy Jackson's Greek Heroes, Hemera is described as a beautiful woman in shimmering blue-and-gold robes.

Abilities
She presumably has a goddess' powers, but is extremely powerful, as she is one of the Protogenoi.
 * Photokinesis: As the Primordial of Day she has absolute control over light.
 * Create illusions/hallucinations.
 * Create light shields/force fields.
 * Project healing energies (different from Vitakinesis).
 * Blast of light to impale or blind enemies for some time or maybe forever.
 * Create a ball or shape of light to blast.

Trivia

 * Hemera's Roman aspect, Dies, spells out the English word dies.
 * In different myths, Hemera is a daughter of Nyx and Chronos (Time), and the mother of Ouranos and Gaea.