The Julian calendar, proposed by Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on 1 January 45 BC, by edict. It was designed with the aid of Greek mathematicians and Greek astronomers such as Sosigenes of Alexandria.
The Jewish calendar predates the Julian calendar and is based on the lunar month, which is a bit longer than 29 ½ days. Because of this, the months in the Jewish calendar are 29 or 30 days long. Twelve lunar months usually amounts to 354 days, 11 days short of a solar year. In order for the festivals to stay in the correct season in relation to the solar year, an extra month is added every few years.
The Jewish calendar is dated from what is supposed to have been the Creation of the earth: 3,760 years and three months before the Christian era. So, to find the current year in the Jewish calendar, one must add 3,759 to the date in the Gregorian calendar. An example, the year 2015 is, in the Jewish calendar, the year 5775. This system, however, will not work to the exact month, since the Jewish year (running on the civil calendar) begins in autumn rather than in midwinter. A Hebrew month begins in the middle of a month on our calendar today. Crops were planted in what we would call November and December and harvested in March and April.
The Jewish Calendar
1 Nisan (Abib) 2 lyyar (Ziv) 3 Sivan 4 Tammuz 5 Av 6 Elul 7 Tishri (Ethanim) 8 Marcheshvan (Bui) 9 Kislev 10 Tebeth 11 Shebat 12 Adar
March-April April-May May-June June-July July-August August-September September-October October-November November-December December-January January-February February-March
Exodus 13:4 1 Kings 6:1, 37 Esther 8:9
Nehemiah 6:15 1 Kings 8:2 1 Kings 6:38 Nehemiah 1:1 Esther 2:16 Zechariah 1:7 Esther 2:7
The Jewish calendar, being lunar-based, invariably began with the new moon. To make up for the shorter year (compared to solar-based calendars), an extra month was periodically inserted between the months Adar and Nisan. That month, sometimes called Veader (“second Adar”), was added seven times within a 19-year cycle (at which time the month Adar received an extra half day).
The names of the months in the Jewish calendar originated in the period following the return from Babylonia to Israel. Before the Babylonian exile, for at least four months had other names: Abib (Exodus 13:4), Ziv (1 Kings 6:1, 37), Ethanim ( 1 Kings 8:2), and Bul (1 Kings 6:38). After the Captivity, these months were renamed Nisan, lyyar, Tishri, and Heshvan (originally Marcheshvan), respectively. The pre-exilic names carried agricultural connotations. For example, Abib (“ear of grain”) signified the month in which grain became ripe; Ziv (“radiance”) was the month for desert flowers to bloom. An agricultural orientation is apparent in what is evidently the oldest Hebrew calendar, found at Gezer (southeast of Tel Aviv) in 1908 and dating from the 10th century BC. The calendar divides the year according to agricultural activities such as sowing, reaping, pruning, and storage.
Primarily, however, the months of the Jewish calendar had religious significance for the Jews and enabled them to commemorate the important events of their history. Each month’s beginning was considered holy (set apart). To ancient Israel, the moon became a symbol of the nation itself; the sun eventually became symbolic of the Messiah (Malachi 4:2). Since the moon produces no light of its own, the symbolism is especially appropriate: Israel was supposed to reflect the Messiah’s light to the world.
The Jewish calendar remained unchanged during the period between the Old Testament and New Testaments (approximately 400 years), despite an attempt by Hellenistic rulers to introduce a modified lunar-month system, presumably of Macedonian origin. According to that calendar, five days were added to the final month of the year, with each of the 12 months containing 30 days. Even then, it only approximated the solar year.
Usually, the ancient Hebrews did not record dates by citing the month and day of an event. Rather, dates were computed by reference to some significant event such as the accession year of the reigning king (2 Kings 15:17) or a patriarch’s birth (Genesis 7:11). In New Testament times, the Jews continued the Old Testament method of dating events by synchronizing them with events either in their religious calendar or within the secular sphere of the Roman world. Writers of the New Testament followed the same practice (Luke 1:5; John 12:1; Acts 18:12). It was only as the calendar reforms of Julius Caesar became embedded in the culture that people changed from that long-standing method to a more standardized system.