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CALENDAR SYSTEMS
Part 1 - Calendar Components and Types

In part 1 of this article, we examine the basic types of calendars and their common components.

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 Calendar Components


Due to the diverse types of calendars and dating systems in existence among the various territories in biblical times, a good working knowledge of various calendar systems is a pre-requisite for gaining a fuller understanding of Bible dating methods.  We’ll begin with a brief look at the various calendar components and types.

By “components”, we mean the ingredients or elements that are common to all calendars, yet also differentiate a particular calendar system (such as the Hebrew, Roman, Julian, Gregorian etc) from others.   The first of two major components is the calendar’s “type”.  This is defined by the purpose and basis of its annual cycle, and the quantity and makeup of its months and days.

The other chief factor is the calendar’s point or date of origin, such as the Creation, founding of a nation, reign of a famous leader, or any other event from which subsequent years are numbered.  In some calendar dating systems, years removed from this origin are typically assigned a descriptor such as BC, AD, BCE, CE, AUC etc; while in others the years are simply designated in the form of, for example “the 15th year of the reign of King Solomon”.  Most dating systems can be applied to the different calendar types.  We’ll address the dating element throughout the article, but we now further expound on the first component.

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 Types of Calendar Systems


Almost all calendars are based on astronomical cycles and can be grouped according to three basic types: “solar”, “lunar”, or “lunisolar”.  Lunar calendars are based upon the moon’s rotation about the earth from New Moon to New Moon (the Hebrew word for moon, chodesh is also translated as “new moon”).  During this one “lunation” or “synodic month”, the moon will completely circle the earth in about 29.5 days (lunar year = 354 days).  A solar calendar is based on the earth’s motion around the sun.  One complete average orbit takes a small fraction less than 365.25 days and is known as a “tropical year”.  This orbit is measured from two consecutive fixed points, usually the northern vernal equinox which denotes the beginning of spring in the northern hemisphere.

The primary benefit of the solar calendar is in its synchronization with the seasons.  This can be a critical advantage when we consider the many industries that are so closely tied to certain seasons occurring at certain times of the year.  The lunisolar calendar attempts to bridge the difference somewhat by following the lunar cycle, but adding additional days to certain months or by adding an additional month every few years.  These leap days or months are sometimes referred to as “Intercalate” Days or Months.

For example, the lunisolar Julian calendar (beginning under Roman Emperor Julius Caesar) has 12 months of 30 or 31 days with February at 28 days, or 29 days on leap years.  Even with these adjustments however, it would eventually be almost globally replaced by the more accurate solar based Gregorian calendar, as we will see in the “Modern Calendar” chapter in part 4.  We can also note that many of the solar calendars published today add the various lunar phases, thus further reducing the need for an exclusively lunar calendar.

In Part 2 - Calendars during Bible Times, we’ll explore the political and historical context of the major nations in which the various calendar systems developed during the biblical era and the early church period.

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