We made the night and the day two outward and visible signs of an inward and spiritual grace. We effaced the light from the entity of the night and put it out in obscure darkness to hide things from view. We made the day a visible entity for objects to be perceptible by the sense of sight in order to betake yourselves to Providence, for His bounty, and in order to know the number of the years. Also to reckon the time occupied by the sun in its apparent passage through the signs of the Zodiac and the period of the earth's revolution round the sun forming a natural unit of time and you be able to compute time and determine it by calculation. And everything did We expound and make plain and abounding in detail.