The Luminarias
On the fourth day God created the great luminary, that is, the sun, to have rule and authority over the day: for it is by it that day is made: for it is day when the sun is above the earth, and the duration of a day is the course of the sun over the earth from its rising till its setting. He also created the lesser luminaries, that is, the moon and the stars, to have rule and authority over the night, and to give light by night. For it is night when the sun is under the earth, and the duration of night is the course of the sun under the earth from its rising till its setting. The moon, then, and the stars were set to lighten the night: not that they are in the daytime under the earth, for even by day stars are in the heaven over the earth but the sun conceals both the stars and the moon by the greater brilliance of its light and prevents them from being seen.