There were once two great beings, twins, equals yet polar opposites. One was Arwid, a being of light, goddess of day; and the other Atlas, being of darkness and god of night. Being of such great contrast, neither could bear to be in the presence of the other, yet, as twins, they were both halves of a greater whole. They knew their divided power was great, but the constant shift between the two could destroy the world.
So, there was only one solution to be found. Each gouged out their own eyes and gave them to the other, Atlas seeing with the eyes of light, and Arwid with the eyes of darkness. Thusly they were united, and with each containing a bit of each other, both were able to be in the other’s presence. And as such, both their realms were affected, each with a part of their opposite. That is why today day still bears pieces of night in the form of shadows, and night pieces of day in the form of stars.