In theory, if one could pinpoint the day on which Zechariah and Elizabeth conceived John the Baptist, one could extrapolate an approximate date of Jesus’ birth. Elizabeth was “in her sixth month” of pregnancy when the angel Gabriel came to Mary. Therefore, approximately fifteen months after Elizabeth conceived, Jesus was born.
The Course of Abijah
The timing of John’s conception is tied to the annunciation to Zechariah while he was serving at the temple (Lk 1). Presumably, within a week or two of his return from Jerusalem, John was conceived. The key, therefore, is to narrow down the dates on which Zechariah would have been serving at the temple. This is a cottage industry among biblical chronologists, but unfortunately the results are more evocative than conclusive because the data are subject to varied interpretations.
What is known for sure is that the priests were divided into twenty-four courses, serving for one week at a time from Sabbath to Sabbath (2 Ch 23:8; 24:7-19; Josephus Ant. 7:14:7). In addition, there were three weeks of the year when all of the courses were on duty: Passover, Pentecost, and Tabernacles (Dt 16:16). Twenty-four divisions each serving two weeks per year, plus the three additional weeks, makes up the fifty-one weeks of a standard Jewish year. (About every third year, an intercalary month was added to the Jewish year to bring it back into alignment with the solar year.) The questions are myriad:
- Did the priests serve the same two weeks every year, perhaps counting from the start of the year? If so, did they calculate the beginning of the year from Nisan or from Tishrei?
- Did the priestly rotation proceed strictly in accordance with the numbering of weeks, without reference to the calendar dates?
- What happened in leap years? Did the priestly rotation simply continue apace, or was there some kind of special arrangement?
- Did the rotation schedule change at any point or was it consistent across the decades and centuries?
Keeping these questions in mind, what are some possibilities? We know from Josephus that the first division, the division of Jehoiarib, was on duty when Jerusalem was besieged during the first week of April, AD 70 (Nisan 1-8, AM 3830). When then would the division of Abijah (the eighth division) have been serving ca. 4 BC? If the courses served in the same weeks of every year, this would have the Abijah division coming on duty
- Passover week: beginning the second Sabbath in Nisan (March-April).
- Pentecost week: beginning the first Sabbath in Sivan (May-June).
- The tenth week of the year: beginning the second Sabbath in Sivan (May-June). (Abijah was the eighth course; the two pilgrimage festivals throws the rotation off by two weeks, resulting in the tenth week.)
- The thirty-fourth week of the year: beginning the second Sabbath in Tishrei (September-October). (Twenty-four weeks later) This places the course of Abijah on duty on the Day of Atonement, Tishrei 10.
- Tabernacles week: beginning the third Sabbath in Tishrei (September-October).
Assuming John was conceived within the week after Zechariah returned from his temple service, the May-June date would yield a date for the birth of Jesus in the fall; if the September-October date is preferred, the result is Jesus being born in winter. In other words, either of the prevailing theories can be supported by this method of calculation!
If, however, the divisions drifted through the year to keep strict time with the count of weeks—and if this week count was not interrupted by leap years—then we can calculate backward from Jehoiarib’s service the first week of April in AD 70.
If we bracket out for the moment the three weeks of the year when all twenty-four courses were on duty, we find by this approach that the course of Abijah would have come on duty during only one week that would yield a Christmas date within our established parameters. A week of service for the course of Abijah would have begun on June 23, 4 BC (Sivan 27, AM 3757).
Assuming John was conceived around July 1-7, this gives a date of the Annunciation around December 30-January 5, 3 BC and a date for the birth of Christ around September 22-28, 3 BC, during the feast of Tabernacles. It should also be noted that the date of the Annunciation by this reckoning falls very close to January 6, the feast of the Epiphany, which in ancient times may have marked the celebration not of the birth of Christ per se, but the fact of the incarnation.
The Day of Atonement?
Taking another approach, some early fathers such as John Chrysostom asserted that Zechariah heard the angelic annunciation on the Day of Atonement. This assertion is suspect from the outset because it seems to be based on an erroneous claim in Protevangelium of James that Zechariah was in fact the Jewish high priest! Even so, we have seen above that a date on or near the Day of Atonement is a possibility if the course rotation was tied to a fixed beginning point (i.e., the first of Nisan) every year. At any event, all the priestly courses would have been serving the following week during the feast of Tabernacles. With that in mind, let us proceed.
In 4 BC, the Day of Atonement (Tishrei 10) fell on Monday, October 1. The following week was Tabernacles, so Zechariah could not return home to Elizabeth for another two Sabbaths, leaving Jerusalem perhaps Sunday, October 14. This means that even if we cannot prove that Zechariah was serving during the first week of October of 4 BC, he definitely would have been serving—along with the other twenty-three courses—during the second week of October, and would not have gotten home until after that.
Let us assume that John was conceived within one week of Zechariah’s return. This would therefore have been October 14-20 (regardless of the precise date of the angelic visitation), with the Annunciation following some twenty-six weeks later around April 14-20, 3 BC. (The angel told Mary that Elizabeth was “in her sixth month.” There is therefore a couple week’s leeway to play with here.)
Finally, the birth of Jesus would come thirty-eight weeks after that or around January 5-11, 2 BC. (Normal human gestation period is considered to be 38 weeks from conception.) It should be noted that this is the only documentary evidence for the date of Zechariah’s service in the temple. All other possibilities are based purely on speculative back-counting. Chrysostom’s testimony, whatever its worth as factual history, conforms rather closely to early testimony for birth of Christ on January 6 (although Chrysostom himself argued for a December 25 nativity).
As tantalizing as this line of speculation is, without some firmer answers about how the courses were scheduled we are left with no strong conclusions. Some calculations favor a fall date for Jesus’ birth, others favor a winter date.
Next: Clement of Alexandria