I'm intrigued about the fourth day of Creation where the heavenly lights were made "for signs and seasons". Astrology comes to my mind, but as far as I know the Bible condemns Astrology.
Genesis 1:14 ESV: And God said, “Let there be lights in the expanse of the heavens to separate the day from the night. And let them be for signs and for seasons, and for days and years.
The ESV footnote has "or appointed times".
Astrology as in the belief that the heavenly bodies control our fate is condemned in the Bible. But there's also astronomy, which is the science used to create calendars.
The Sun and the Moon are for times and seasons and a good calendar takes both into account. Months, even today, are based loosely on the lunar cycles. The lunar cycle takes about 29.5 days to complete, which is why months alternate between 30 and 31 days (i.e. due to the fractional .5). The reason we use 30/31 rather than 29/30 and have February as only 28 or 29 is to keep the year at the 365.24 days required for the solar year. The fractional part (which goes beyond .24) is why we need leap year. So the calendar is a balancing act between the Sun (which requires 365.24 days) and the moon (which requires months of 29.5 days).
Different solutions were used in ancient calendars (such as an extra 13th month in leap years, with leap years obviously being based on a different calculation), but the basic idea has always been the same since the beginning: to use astronomy to create a calender that balances the requirements created by the movements of the Sun and the Moon as they were understood at the time.
Knowing what month it was was very important in the Old Testament to keep the appointed feasts at the right time, like Passover, Tabernacles, etc.
The Hebrew calendar as it is used today, based on rabbinical calculations, has 12 months alternating between 29 and 30 days long, with an extra 13th month on leap years. A whole month is added on leap year because the year normally has only 354/355 days in it, which means there are more days to make up to get back on track with the Sun on a leap year (every 19 years), and the calculation doesn't truly accomplish this perfectly.
Also of interest may be the Babylonian calendar, Lunar phase, Tropical year.
My hermetic concept of astrology is that God controls our fate, as he controls the movement of the planets. We can observe the positions of the planets and use these to infer the state of certain "energies" at the present time. Furthermore, knowing how those energies change over time allows us to determine whether the universal forces present will be working for or against our plans, and helps us to decide when to take or withold action for the most positive outcome. It is not the case that the planets control our fate, but their positions do reflect the state of various mysterious energies and so function as useful indicators. Certainly this is what was meant in Genesis 1:14, when HE said "Let them be for signs (and seasons and days and years)" You will notice that the word 'signs' is not needed to explain the astronomical calculations which were separately used to mark time as described in the earlier answer.
