Calendars More Than Just Days and Months

Calendar image from CMI

Is there no certain rule by which calendars ought to be formulated?

by David Malcolm

The Chinese calendar and the Islamic calendar seem strange to those of us who have been brought up in the West.

There is something seemingly strange with New Year coming at the end of January (or a few days before, or a couple of weeks after); or the month of Ramadan falling earlier and earlier each year. One may ask: How are the Muslims supposed to know when to plant their crops? If some date on their calendar is chosen, before very many years it will be completely out of tune with the seasons. The unfamiliar features of the Islamic calendar can be accounted for on the basis that it is a lunar calendar which means a month is very accurately tied to the phases of the moon.

The moon proceeds through its phases in a cycle of about 29.5 days (called the ‘synodic’ month), so having months alternating between 29 and 30 days keeps closely in step with the moon.

A new moon signals a new month and a full moon the middle of the month. This idea is not foreign to our western culture. The Shorter Oxford dictionary notes that the word ‘month’ is derived from the word ‘moon’. The primary definition of month is given as “a measure of time corresponding to the period of revolution of the moon”. So the idea of a lunar month is logical. On the Islamic calendar a sequence of 12 of these lunar months make up a year.

The Chinese calendar is more complicated. It is often popularly referred to as a lunar calendar, but is actually a luni-solar calendar.

It has months which are tied in with the phases of the moon as does the Islamic calendar, but additionally it keeps the year in step with the seasons in the long term by having some years with 13 months. Again that seems strange to us. Surely there should be 12 months in a year?

Is there no certain rule by which calendars ought to be formulated? Some yardstick to provide the various ethnic groups with a basis for designing our calendar? Do we not have some absolute standard that will enable us to say that some calendar features are unacceptable?

In fact, we do have such a yardstick. The Bible sets out God’s provisions:

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, and let them be lights in the expanse of the heavens to give light upon the earth.” And it was so. And God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars. And God set them in the expanse of the heavens to give light on the earth, to rule over the day and over the night, and to separate the light from the darkness. And God saw that it was good. And there was evening and there was morning, the fourth day. (Genesis 1:14-19)


So God’s word tells us that He provided the astronomical cycles for us to determine time periods (seasons).

The day-night cycle, caused by the earth’s rotation defines the day for us; the phases of the moon give us the month; and the motion of the stars, moving full circle over about 365 days sets the year for us. And there is no requirement here for there to be 12 months in a year.

No calendar conforms with God’s provision, and it comes as a bit of a shock to realise that the Roman calendar likewise falls short.

That calendar we are all familiar with—that was adopted by the early church and has become the standard world-wide—is deficient. In fact, just as the Islamic calendar is defective because it has a year arbitrarily made up of 12 lunar months, so the Roman calendar is defective because it has a month which is just an arbitrary division of the year into 12.

The Hebrew calendar has been used by the Jewish people for many centuries, and is still in use today. Like the Chinese calendar, it has months alternating (generally) between 29 and 30 days, to keep in step with the lunar month, and also keeps in step with the solar year in the long term. It has a fixed cycle containing seven 13-month years in every 19 years.

The Week

We have seen that the day, the month and the year had their origins in astronomical periods, which God instituted for that purpose. But the week is different. It is not based on any observable astronomical period. The origin of the seven-day week is set out in Genesis when God completed His creation, setting a pattern for His creatures (Genesis 2:2-3 and Exodus 20:11)…

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image credit: Creation Ministries International 2019 Calendar