Because calendars are culturally constructed systems, there are several important differences between the modern calendar and the calendars used in biblical times. When dealing with ancient Jewish and early Christian sources, we can reconstruct complete calendar systems. However, the Bible itself, written over many centuries, employs several calendar systems and systems of dating. No single normative calendar system emerges from biblical materials. Nevertheless, many aspects of life in biblical Israel depended on the use of calendars, which regulated religious festivals, agricultural activity, various aspects of the legal system, and the recording of historical events.
Measurement of Time in Antiquity
There were several methods of reckoning time in antiquity. Some units of time corresponded to the observation of celestial phenomena (see Gen. 1:14), such as the rising and setting of the sun (defining the day), the waxing and waning of the moon (the lunar month), the ascension of the sun in the sky at noon (the solar year). Other measurements of time were defined by the agricultural cycle, including planting and the beginning and end of the harvest (see Exod. 23:16; Ruth 1:22). An agricultural scheme serves as the basis of the Gezer Calendar, an important archaeological object of the tenth century BC unearthed about thirty miles northwest of Jerusalem. The Gezer Calendar divides the year into eight periods of one or two months, each of which corresponds to the planting, tending, and harvest of various crops. Still other units of time, such as the seven-day week and the lunisolar year (see below), were derived by counting or calculation and did not correspond to any observable celestial or terrestrial phenomena.
The division of days into hours and minutes is possible in modern times because of mechanical and electronic timepieces. Without these devices, divisions of time shorter than the day would have been approximations at best. Biblical texts refer to dawn, morning, noon, evening, night, and midnight. In NT times, the twelve daylight hours were numbered (Matt. 27:45; John 11:9). There was also a system of dividing the night into “watches,” attested in both the NT and the OT.
The Month and the Year in the Bible
The Hebrew words for “month” are related to the words for “moon” and “new” (i.e., the “new moon”), which suggests that the ancient Israelite month was a lunar month corresponding to the waxing and waning of the moon over a period of twenty-nine or thirty days. The Bible refers to numbered days in each month, as high as the twenty-seventh day.
There are several systems of naming the months in the Bible. Four “Canaanite” month names appear in the OT: Aviv (the first month), Ziv (the second), Ethanim (the seventh), and Bul (the eighth). Because of the infrequent use of these names, some scholars have questioned whether this system was in widespread use in ancient Israel. The names probably are derived from agricultural terms.
In many cases the months are simply numbered. In this system, the first month began in the spring season. According to biblical narrative, this way of reckoning the beginning of the year was commanded to Moses at the time of the exodus (Exod. 12:1). However, the Bible applies this scheme to events much earlier, as in the story of the flood of Noah, which began in the second month (Gen. 7:11), and scholars have associated the numerical system of months with late biblical sources, around the time of the exile. The system may have come into use around that time and replaced an older system.
In some late biblical texts Babylonian month names are adopted, including Nisan (the first month), Sivan (the third), Elul (the sixth), Chislev (the ninth), Tebet (the tenth), Shebat (the eleventh), and Adar (the twelfth). Following biblical usage, the Babylonian month names were adopted in the ancient Jewish calendar, which is still in use today.
Based on references to the “twelfth month,” the Israelite year apparently consisted of twelve lunar months. Accordingly, the lunar year consisted of approximately 354 days, which means that it would not have corresponded to the solar year of approximately 365¼ days. The beginning of the year would have drifted between eleven and twelve days each year. Presumably, this would have been an unacceptable situation, given the fact that many of the biblical festivals were both assigned to lunar dates and were correlated to agricultural events. The problem probably was solved through the intercalation of “leap months,” as was the practice in maintaining the later Jewish calendar. The result is a lunisolar calendar, in which the year is composed of twelve lunar months and is corrected relative to the solar year by the periodic addition of a second Adar (Adar II) seven times in every nineteen-year period. The Bible does not mention this procedure or identify who was responsible for maintaining the calendar in ancient Israel.
Modern systems of absolute dating, in which all years are numbered relative to a single historical reference point—for example, the birth of Jesus (Anno Domini), the journey of Muhammad in AD 622 (Anno Hegira 1) from Mecca to Medina in Islamic culture, and the creation of the world (Anno Mundi) in Jewish tradition—were unparalleled in biblical times. Instead, events were usually dated relative to the reigns of kings, Israelite or otherwise. For example, the accession of Abijah is dated to the eighteenth year of Jeroboam’s reign (1 Kings 15:1), and the proclamation of Cyrus is dated to his first regnal year (Ezra 1:1). In other cases, events were dated relative to important historical events. The beginning of Amos’s career as prophet is dated to “two years before the earthquake” (Amos 1:1), and Exod. 12:41 dates the departure from Egypt to the 430th year of the captivity. In other instances, the fixed points on which relative dates are based cannot be determined. The beginning of Ezekiel’s career as a prophet is dated to the otherwise unspecified “thirtieth year” (Ezek. 1:1). The verse may simply refer to Ezekiel’s age.
The same practices of dating events are followed in the NT. The birth of John the Baptist is dated to “the time of Herod king of Judea” (Luke 1:5). The census of Caesar Augustus is identified as “the first census that took place while Quirinius was governor of Syria” (Luke 2:2). As in the OT, such formulas presuppose that the reader has a basic awareness of the succession and reigns of kings and emperors—an advantage lost to modern interpreters, who continue to debate the absolute dating of these events. Perhaps analogously to Ezek. 1:1, the beginning of Jesus’ ministry is dated to his thirtieth year of age (Luke 3:23). Other events and persons reported in the NT can be correlated to extrabiblical historical records to establish absolute dates for biblical events (e.g., the death of Herod Agrippa I in AD 44 [Acts 12:23]). These are distinct from instances in which biblical authors are making a conscious effort to provide dates intelligible to their readers. In contrast to OT historical narrative, for the most part, the NT shows little interest in dating events in its narrative, even according to ancient conventions of relative dating.