Sometimes, when you're deep in the countryside, you meet three girls, walking along the hill tracks in the dusk, spinning. They each have a spindle, and onto these they are spinning their wool, milk white, like the moonlight. In fact, it is the moonlight, the moon itself... All they have to do is to see that the world gets its hours of darkness, and they do this by spinning the moon down out of the sky. Night after night, you can see the moon getting less and less, the ball of light waning, while it grows on the spindles of the maidens. Then, at length, the moon is gone, and the world has darkness, and rest, and the creatures of the hillsides are safe from the hunter, and the tides are still.
Then, on the darkest night, the maidens take their spindles down to the sea, to wash their wool. And the wool slips from the spindles into the water, and unravels in long ripples of light from the shore to the horizon, and there is the moon again, rising above the sea, just a thin curved thread, reappearing in the sky. Only when all the wool is washed, and wound again into a white ball in the sky, can the moon-spinners start their work once more, to make the night safe for hunted things.
-- from "The Moon-Spinners," by Mary Stewart (c) 1962