This study is based on a world-view that Yahweh created the heavens and the earth and everything therein (including you and me). If that isn't your world-view, you may benefit from that study first. Otherwise, what is your theory about WHY Yahweh arranged the sun and moon in such a way that the sun appears at the beginning of every day and disappears at the beginning of every night? And why does the moon change in size and shape repeatedly every month, waxing until full, then waning until dark? We don't have to guess.
And Elohim said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs [weeks], and for seasons [months], and for days, and years: And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so. And Elohim made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also. And Elohim set them in the firmament of the heaven to give light upon the earth, And to rule over the day and over the night, and to divide the light from the darkness: and Elohim saw that it was good. And the evening and the morning were the fourth day.
Yahweh is timeless and needs no time. Eventually, when everything is restored, time will be no more (Revelation 10:6, Revelation 21:25). Yahweh created time for us and placed the lights in the heavens for our time keeping - His great clock and calendar in the sky. You and I don't need a watch to tell if it's night or day. For centuries men knew that these lights also told them the day of the week, the day of the month, and the beginning of the year. Most of these ancient, simple technologies have been lost today.
Yahweh's time keepers are accurate, self-correcting and universal - easily seen by everyone. They served nearly the whole world for more than 4,000 years. It's time for us to get back to nature and closer to the Yahweh of nature.
"And Yahweh saw that it was good."