Hemera

In Greek mythology, Hemera (Greek: Ἡμερα, "day"), also spelled as Amera (Greek: Αμερα) or Amara (Greek: Αμαρα), was the personified goddess of the day. Hesiod states her to be the daughter of Erebus and Nyx. However, Bacchylides states Hemera is the daughter of Chronos and Nyx but Hyginus states that she is the daughter of Chaos and sister of Nyx.

As the goddess of the day, Hemera is the female counterpart of her brother and husband, Aether. Hyginus writes that their children are Uranus, Gaea, and Thalassa. However, Hesiod lists Thalassa as their only child.

In Roman mythology, Hemera was closely identified with Dies.

Day and Night
In Hesiod's Theogony:

Nyx and Hemera draw near and greet one another as they pass the great threshold of bronze: and while the one is about to go down into the house, the other comes out at the door.

Hemera and her mother are the reasons for the continuous cycle of day and night. Together, they lived in Tartarus and as one entered their home, the other left to bring about their abode upon the earth: Nyx the night and Hemera the day.