Philo Judaeus De Opificio Mundi 55

But the Creator having a regard to that idea of light perceptible only by the intellect, which has been spoken of in the mention made of the incorporeal world, created those stars which are perceptible by the external senses, those divine and superlatively beautiful images, which on many accounts he placed in the purest temple of corporeal substance, namely in heaven. One of the reasons for his so doing was that they might give light; another was that they might be signs; another had reference to their dividing the times of the seasons of the year, and above all dividing days and nights, months and years, which are the measures of time; and which have given rise to the nature of number.