Its all fun and games until someone loses their sanity.
He was conceived when Asteros seduced Epithymia. Their passion was such that two balls of fire were placed inside the womb of Epithymia and in one day, she birthed the sun (Ilios) and the moon (Nyktos).
The twins were taken from their mother and placed in the sky so that Asteros could share his domain with them. He split rulership of the sky between his sons giving Ilios control of the day and Nyktos control of the night. It is said the two brothers often embrace each other as they pass, thus giving the times when both the sun and the moon are visible to those who reside on earth.