In the book of Genesis, it is written that God made two great lights, the greater light to rule the day and the lesser light to rule the night. This means that the two lights, the sun and the moon, have been created to rule over the day and the night respectively.
They also demarcate the difference between day and night and provide light to the world. The sun is responsible for giving light and heat during the day, while the moon reflects the sun's light to illuminate the night sky. This cycle of day and night, governed by the sun and the moon, has been a fundamental part of the natural world since the beginning of time.