Then God said, “Let lights appear in the sky to separate the day from the night. Let them be signs to mark the seasons, days, and years. Let these lights in the sky shine down on the earth.” And that is what happened. God made two great lights—the larger one to govern the day, and the smaller one to govern the night. Genesis 1:14-16
On Day 4 of the Creation Week, the celestial bodies are made by God and in the scripture text we are told of their primary purposes.
To separate day from night;
To mark the seasons, days, and years; and
To shine down on earth.
What is interesting is the order in which these purposes are presented. Normally, in providing a list of significance or rationale, the most important factor is listed first with other factors listed next in an order of decreasing significance. Notice that in the Day 4 list, providing light to the earth is tertiary in significance. This may be because light was already present since the first day of the Creation Week with the Creator Himself as the source. (Refer to my earlier blog: The Day Light Arrived.) If we combine the first two purposes, God made the sun, moon, and stars to mark time ... day and night, months, seasons, and years.
You [God] made the moon to mark the seasons, and the sun knows when to set. Psalm 104:19
In His infinite wisdom, God saw it important to mark time and changes in time with celestial bodies. You might say that on Day 4 of the Creation Week, God established the calendar. He did so by positioning and putting into motion the earth, moon, and sun in such a way that there would be a reliable cycle of repetitiveness - a regular reoccurrence of celestial driven events to make life on earth not only function but constantly changing.
In creating the sun and moon, God brought definition to day and night. Because this occurred on Day 4, and because the text has already stated three times "and evening passed and morning came, marking the ___ day", I believe the earth was already rotating and God, being the initial light source, was providing the light to distinguish day and night. But, now on Day 4, God provides another light source, the sun, to rule the day, and the lesser light, the moon, to govern the night. How long does it take for the earth to make a complete rotation? Well anyone with a clock knows - 24 hours. Right? Well, perhaps. It depends upon your perspective. The earth rotates once in about 24 hours with respect to the sun. Meaning, that 24 hours from now, the sun will be in nearly the same position; which is known as a solar day. But, in respect to the stars, it rotates once every 23 hours, 56 minutes and 4 seconds, which is known as a sidereal day. This is why stars appear to rise four minutes earlier every night. (In actuality, it is not their movement you are observing, it is the earth that is moving.) The sidereal day is the reason why different constellations are only visible at specific times of the year. Constellations, however, are in the same location at the same time of the year every year. They mark the seasons.
Month and moon come from the same word, mōna. It is an Old English word that shares its origins with the Latin words metri, which means to measure, and mensis, which means month. So, the moon is called the moon because it is used to measure the months.
The moon takes approximately one month to orbit around the earth (27.3 days to complete a revolution, but 29.5 days to completely go through all of its phases such as full moon to full moon). As the moon completes the 27.3-day orbit around earth, both the earth and the moon have traveled some distance around the sun. Therefore, it takes another 2.2 days for the sunlight reflecting off the moon to match exactly to what it was at the beginning of the lunar cycle. The moon's regularity and the pattern of reflected sunlight on the moon helps to mark time. It provides 12 segments of time in a solar year, and it also helps to mark time during the night. Before clocks and iPhones existed, the moon was used to help identify the passage of days during the month and the passage of hours during the night.
Seasons and Years
We saw earlier that the earth's rotation measure days and nights. But, God added a significant and vital enhancement to His creative work. He made the earth's rotational axis to be tilted by 23.5 degrees. This combined with the rotation around the sun in 365 days gives us seasons. The earth revolves around the sun in 365 days, 6 hours, 9 minutes with reference to the stars. (The 6 hours, 9 minutes adds up to about an extra day every four years. This is why we have a leap year on February 29 every four years to accommodate for the extra day.) So when the axis is tilted towards the sun that portion of the hemisphere has longer days and experiences summer and when the axis is angled away from the sun the days are shorter and it is winter for that portion of the earth.
It is apparent from the Genesis creation account that seasons and marking of time was an important and intentional part of God's creative work. It is also apparent that these measurements of time and seasons were not a human invention. God established them with celestial bodies that only the Creator could have placed in the heavens. So it should not be a surprise that much in scripture is dependent upon and references seasons. This includes the Jewish holidays and festivals. Not only did the actual annual feasts followed the seasons, but also their prophetic fulfillments are linked to the seasons. It is as if God wanted us to track time and mark seasons.
For everything there is a season, a time for every activity under heaven. Ecclesiastes 3:1
On Day 4, God created and placed the sun, moon, and stars to mark time for days, months, seasons, and years. But there is one very common measurement of time that we have yet to discuss - weeks. All other measurements of time are based on celestial movements, but what about the 7-day week? True, it is about one fourth of a lunar cycle and could be linked to it. It also has pagan roots in the Babylonian and Roman empires. The names for the days of the week actually originate from the names of the planets which were named after the Grecian deities. But, civilizations and cultures throughout history have never deviated far from the seven-day week. Why is that? I believe it is because of the Creation Week. All other time periods were established by created celestial bodies, and it makes sense that we do not change these periods of time because it would be like changing the course of the earth or moon. But, why has not any culture successfully changed the length of a week, since there is nothing that is really holding us to it. I believe that God placed that time period in our very souls as part of the seven literal days of creation. How else can you explain why atheistic cultures have not strayed from it? To me it shows that there is a greater "gravitational pull" than exerted by the sun, earth, or moon, and that is the pull of the human race to its Creator.
He has made everything beautiful in its time. Also He has put eternity in their hearts, except that no one can find out the work that God does from beginning to end. Ecclesiastes 3:11