God assigned purposes for the sun and moon. They were to:
- separate the day from the night. [Their orderly appearance day after day and night after night gave a sense of continuity and structure.]
- serve as signs to mark seasons and days and years. [not in the sense of astrology, but indicating upcoming changes of seasons, or other matters such as planting times, etc. I imagine that the appearance of certain astronomical events (constellations, etc.) would also indicate the passage of years, etc., to help people recall when significant events in history had taken place.]
- govern the day and the night
- give light to the earth
God also made the stars. At first this passage may seem to be saying -- "oh, yeah, God also made the stars." -- as though this was not really an important matter. However, Psalm 136:9 says that the stars help the moon to govern the night. Some stars are well-known indicators of direction, like the North Star. The appearance of certain constellations could indicate seasons.
Did you know that God even named each individual star? Isaiah 40:25-26 (NIV) says so: