1. The early societies used the full moon as a measure of time. Time from one sunrise to the next was one day and from one full moon to the next was a larger unit. This system came in before the units of 7 day week and 365 day year came into being.
2. Very early in prehistory sea voyage had started. When they were far from shore for days the only direction for them were the position of stars and constellations in the night sky.