Which day did God create the sun and moon?

Since the sun and moon are included in "the heavens" mentioned in Genesis 1:1, they were created long before Day Four. On the fourth day God proceeded to "make" these celestial bodies occupy a new relationship toward earth's surface and the expanse above it. When it is said, "God put them in the expanse of the heavens to shine upon the earth," this would indicate that they now became discernible from the surface of the earth, as though they were in the expanse