When did Zacharias receive his angelic visitation in the temple? When did important events fall in the Savior's life? The Qumran calendar may open up a key to understanding more about the "when" of significant moments in our sacred history.

In this, the first of two parts, John C. Lefgren and John P. Pratt lay the foundation for comprehending how the Qumran calendar functioned and in the next article they will use their findings to shed light on important dates in the life of Christ.

The Dead Sea Scrolls have provided a wealth of information about religious practices during the first century or so B.C. in the community at Qumran near the Dead Sea. A surprisingly large portion of the scrolls deals with keeping time, which was essential for knowing exactly when the sacred feasts prescribed in the law of Moses should be celebrated.^[1] The scrolls make it clear that the group at Qumran felt that the other Jewish sects were mistaken in the calendar they were using, which was based on the phases of the moon. This was probably one of several reasons that caused them to withdraw from Jerusalem and to celebrate their own feasts at the times they felt were proper according to what has become known as the Qumran calendar.

Some of the scrolls provide long lists of dates and ample detail about the calendar, but apparently no one has correlated the Qumran calendar to our Gregorian calendar. That is, when the scrolls speak of a certain date on which a festival was held, just exactly what date did that correspond to on our calendar? The best correlation to our calendar so far is that the two principal calendar scrolls date to about 50-25 B.C., based on the style of handwriting.^[2] Fortunately, that is much more precise than the dates ascribed to the entire set of scrolls and the community in general, being from the late second century B.C. through the destruction of the temple in A.D. 70.

The purpose of this article is to attempt to correlate the beginning date on the two principal Qumran calendar scrolls to our calendar. Having done that, and found independent corroboration, we can then answer a long standing historical question about when each course of priests officiated in the temple at Jerusalem. Resolving that problem has implications for to all of Judaism, not just the sect at Qumran. Next month's article will focus on what it means to Christian chronology.

The Calendar of Qumran

While several documents discovered at Qumran give schedules of events according to their calendar, the best descriptions of the workings of the calendar itself are probably found in the Book of Jubilees and the Book of Enoch.^[3] Although those books are not included in our Bible today, both were held in high regard at Qumran, equal to others we now include in the Old Testament.

The calendar had 364 days each year, beginning on a Wednesday every spring. It had four quarters of exactly 13 weeks each, so that every quarter-year began on a Wednesday. Each quarter had three months, the first two having 30 days, and the third having 31 days. The months were numbered from 1 to 12, beginning in the spring. Thus, it had a feature desired by many modern businessmen: it was so tightly tied to the week that every day occurred on the same day of the week every year. In particular, their sacred feast days always occurred on the fixed days listed in Table 1.^[4]

Cave 4 is the nearest to Qumran.

Of course, having only 364 days, the calendar year was 1.24 days short of a true solar year of 365.24 days. They must have had some method for inserting an extra week often enough to keep this calendar aligned with the seasons, because some of the offerings, such as First Fruits, had to occur at certain seasons of the year, when the barley or wheat would be ripe. While scholars have acknowledged that an intercalation system was needed (meaning inserting extra days to align with the solar year), they have noted that no method is mentioned in the scrolls.^[5] In this article, we both attempt to precisely date one seven-year period, as well as propose a possible intercalation method.

The Priest Cycle

Before proceeding to date the Qumran Calendar, we need to understand what we shall call the Priest Cycle. Officiating duties at the Temple of Solomon were divided among 24 families who descended from Aaron, the brother of Moses (1 Chron. 24:1-18). These family divisions are usually translated "courses" in the Bible (1 Chron. 23:26, Luke 1:5). A priest from each family presided at the temple for one week, beginning about midday every Saturday.^[6] Their names and the order in which they presided are given in Table 2. Thus, it took 24 weeks to complete the entire cycle. If this calendrical cycle could be correlated to a known date, and if it were known to be continuous, then the cycle could potentially be used to establish other historical dates. For example, when the angel Gabriel appeared to the priest Zacharias in the temple, he was on duty representing the course of Abijah (Luke 1:5-20). That course only officiated every 24 weeks, so it would be a big clue to when that event occurred if it were known when that course officiated.

Qumran and Dead Sea as seen from a cave.

So what has this priest cycle got to do with the Dead Sea Scrolls? It turns out that the scrolls may be the key to understanding the Priest Cycle because all of the calendrical tables of events include not only the day of the month and week, but also the name of the course officiating during that week. That does not mean that the society at Qumran was in charge of making the roster for temple priesthood service. Rather, it was simply the accepted convention to name every week. It was an excellent way to have a double check on exactly what date is meant, and provides a way to detect copyist errors. For example, today we often include the week day along with the date on invitations, such as to wedding receptions. That serves as a reminder as to exactly what date is intended. The method used at Qumran to refer to a Wednesday was, for example, to call it 4 Gamul. The means the fourth day (Wednesday) of the week called Gamul (which was when that priestly course served in the temple). Days of the week at that time were simply numbered from Sunday, being the first day of the week. Saturday was simply referred to as the sabbath, usually meaning the day the new priests began duty, rather than the last day of their duty. It is really fortunate that this method of giving both a day and month as well as week day and week were used to record events in the scrolls because errors in the scrolls can be immediately detected. And a compliment is due for the scribe because there are only a handful of mistakes in hundreds of dates listed.

Seven Year Cycle

The scrolls also give us one big clue about how the Qumran calendar might have been intercalated. The two most famous and detailed calendar scrolls are called 4Q Calendar Document A and B (also called 4Q320 and 4Q321) because they were found in the 4th cave discovered at Qumran. The latter ("Scroll B") is a continuous 7-year listing of events: one year of dates of lunar observations followed by a 6-year list the dates of both lunar events and also the feast days and how the beginnings of each month aligned with the week and priest cycle. It is clear that every year in that period had exactly 364 days. This table also establishes that the Priest Cycle was understood to be a continuously repeating cycle, which is confirmed by other Hebrew writings.^[7].

Entrance to Cave 4, where Calendar scrolls were found.

The fact that it is a 7-year listing with the last 6 years treated as a separate entity is an important clue. It means they had almost certainly noticed that six years completes a cycle where the same priest would again be officiating on New Year's Day. That is, 6 years of 52 weeks each exactly equals 13 Priest Cycles of 24 weeks (6 x 52 = 13 x 24 = 312 weeks), so the two cycles would begin to repeat.

Sun Rises in East

This method for beginning the year is very different from the method used in Jerusalem at the time. On the Judean calendar, the spring New Year's Day occurs at a new moon, chosen such that the next full moon occurred on or after the spring equinox.^[10] Because the equinox occurs on March 20/21 on our calendar, that means that the Judean calendar could begin as early as March 7 (because the new moon is two weeks before the full moon), whereas the Qumran calendar year would have begun on a Wednesday about March 21.

Astronomers at Qumran would have been aware that the way their calendar worked is that every year the true equinox would come earlier by about 1 1/4 days. That means that when they inserted an extra week, they would pick the first Wednesday after the true equinox, rather than before. To see this, let us remember that the way our Gregorian calendar works is to insert a leap day on February 29th nearly every 4 years to keep the spring equinox on March 20/21. The Qumran calendar apparently has an uninterrupted span of 7 years, each of 364 days, so that after seven years, it loses 7 x 1.24 days = 8.68 days from the true year. So, ideally, the 7 years should begin about 4 days after the equinox (March 25th), so that each year thereafter would begin about 1.24 days earlier. That way, after three or four years, the year would begin very near the true equinox and still be on a Wednesday. After seven years, the beginning would be on March 16-17th, and it would be time to insert an entire extra week so that the cycle could begin again about March 23 24th. But that extra week would not quite make up the deficit of 8.68 days. Adding 7 days every 7 years makes the average year become 365 days rather than 364. If one more week were added every 28 years then the average year length would be 365.25 days, which is an excellent value.

The main point here is that the ideal time for the Qumran calendar to begin a seven year cycle is the first Wednesday after the spring equinox. The sun rises at different places along the eastern horizon every day, and makes an annual circuit from the southeast through northeast and back during the seasons. The time when the place of sunrise on the horizon changes the most is at the spring and autumn equinoxes, the two days of the year when the sun rises most nearly due east. At that time the shift in the position of the sun as it rises on the horizon is more than two solar diameters every day, so it is easy to determine the precise day when the sun rises most nearly due east.

Qumran Sundial

Qumran Sundial could determine the equinox.

If our understanding of how the calendar was intercalated is correct, then those at Qumran would need a way to determine the day on which the sun rose due east. Many ancient cultures did that by erecting a pillar or marker to align with a mountain peak or other horizon feature. Stonehenge in England is a classic example, but it aligned with the summer solstice rather than the spring equinox. Is there any physical evidence at Qumran that they were interested in determining the day of the vernal equinox?

Here the answer is a resounding "Yes." A limestone sundial has been discovered at Qumran. It was designed to measure the sun during the year rather than during the day. After studying it, two researchers concluded:

Thus, there is strong supporting evidence that the Qumran calendar was indeed intercalated with a method involving actually measuring when the sun arose in the east, as directed by the Book of Enoch.

"First Year"

Note also that in the above quotation from the scrolls that the beginning day of the six-year period is called the first day of "the first year." First year of what? To answer this, we must remember that the Lord instructed Moses to count years by sevens (Lev. 25:4). Most likely, it the "first year" meant the first year of a 7-year cycle, and that the year listed before it was the last (sabbatical) year of the previous cycle. This suggests that the intercalation of an extra week of days which would be needed to keep synchronized with the seasons probably came at the end of the sixth year of the 7-year cycle. That is consistent with the fact that the Judean lunisolar calendar was also often intercalated in the 6th year to minimize the length of the year when crops were not available.^[12]

Thus, the current state of understanding is that the Qumran calendar has a year of 364 days comprising 12 months of 30 or 31 days each and has holy days occurring every year on known fixed days. Moreover, the Priest Cycle was uninterrupted for at least one 7-year period. What has not been known is just when that 7-year period occurred, except that it is estimated to have begun about 50-25 B.C. Let us now attempt to discover the precise date of that 7-year listing.

The Correlation

If all the information that the scrolls contained were a list of the dates of the beginnings of the months, the feast days, and the courses of the priests, then the scrolls might have begun on any Wednesday at all in the historically plausible time period. That is because we have not known exactly when the priests served, or even if they served as one continuous cycle. Thus, if one starts on any Wednesday near the spring equinox, which is assumed to be the week of Gamul, then all of the first days of the months and the feasts will fall in exactly the priestly weeks listed (except for scribal errors). It would tell us that indeed we have the dates of the feasts correct, and that they occurred on the same days of the Qumran year annually, but that is all. It would be of no use whatever to indicate the starting year.

Lunar Phases

Fortunately, the same two calendrical scrolls mentioned above provide another set of clues. They give many dates of the last day of the lunar month and also of the full moon. We are not aware of anyone who has attempted to correlate this listing of the moon's phases to the known lunar phases during the possible time period, so we will now describe out approach to do that.

Scroll A includes a listing of the last day of every lunar month. Even though the words "last day of lunar month" are not found there, the meaning is clear because there are alternate listings as the "29th" and "30th" every month, correlated to the date and week day. The true lunar month contains 29.53 days (the period between new moons), and so an excellent approximation is simply to alternate months of 29 and 30 days, for an average value of 29.5 days. Scholars apparently agree that the last days of the lunar month are indicated. In all cases known in the ancient world, the lunar month begins at the new moon, and that is our hypothesis.^[13]

Fragment of Calendar Document B (4Q321).

Perhaps one reason that the scrolls have not been precisely dated in the fifty years since their discovery is that there is uncertainty as to what is meant by the last day of the lunar month. There is a one to two day period when the moon is invisible during every cycle of phases. The last day of the lunar month might refer to the last day the thin crescent is visible before dawn, or it could be day of the new moon, or even the day after when the new crescent may still not be visible after sunset. This latter was the interpretation of those in Jerusalem at that time. Thus, there is a three day uncertainty which makes it hard to know just what phase is implied, and hence difficult to pinpoint any date.

We propose that the key to solve the problem is to focus on the full moons, which are also listed. Observing the full moon is a better reference point because it is independent of the details about how the month begins. In other word, while "new moon" is of uncertain meaning, "full moon" has always meant "when the moon is fully illuminated." Fortunately, scroll B lists dates for the full moon for the same three-year period, along with also repeating the listing of dates of the end of the lunar month for those years. It then continues through the six-year period with the dates of the holy days and first days of each month. Because the lunar cycle lasts 29.53 days, and begins at the new moon, we need only correlate the full moon days listed with the phase of 14.76 days because the full moon occurs halfway through the cycle, on the average.

Focusing on the full moons immediately makes it clear how the end of the lunar month was defined. The last days of the month are nearly always listed as occurring 13 days after the full moon, whether or not the month has 29 or 30 days. That means the last day is on day 27.76 on the average (14.76 + 13 = 27.76). That is nearly two full days before the new moon (on 29.53), so it indicates that the last day of their month was the last day that the old crescent was visible before dawn. That is very different from how things were done in Jerusalem where new crescent was observed, but is consistent with one proposed method for how a Galilean calendar might have been regulated.^[14] Thus, at Qumran, the first day of the month was apparently the first day that the moon was not visible.

From Table 3, we see that the most likely date for the beginning of the first year of the Qumran sabbatical cycle is either Wed 25 Mar 42 B.C. or Wed 21 Mar 39 B.C. They both occur during the period when the scroll was written and each has an error of only 0.3 days from the recorded lunar phase. One thing that favors the first date is the symmetry between the two dates. With both of them having the same discrepancy from the true full moon, we would expect that if the first date were the correct starting date, then the second date would be listed in the 6-year listing has having exactly the same lunar phase. Checking the listing we find that is true: the first day of the fourth year is also the last day of the lunar month, just as was the first day of the first year:

No too much weight should be given to this coincidence because it would only be off by one day at most in any case. Nevertheless, it does favor the earlier date because the synchronism is perfect.

Sabbath Year Cycle

Another point in favor of the 42 B.C. choice is that it agrees with one of the proposed years for the 7-year sabbatical cycle of the other Jewish sects of the time. While those at Qumran differed with others about the kind of year to use, they might well have agreed with them about the 7-year count. We do not wish to make too much of this coincidence because the sabbatical cycle has been a subject of debate,^[18] and even if it were known, it might not have agreed with the Qumran group. It does appear to be, however, supporting evidence that the counts may have agreed.

Now let us consider a second witness that the date Wed 25 Mar 42 B.C. is indeed the correct choice to be the first day of the first month of the first year of the Qumran tables.

Corroboration

Fortunately, there exists strong supporting evidence, totally independent from the Dead Sea Scrolls, that we have indeed found the correct date. In A.D. 70, Titus led the Roman Army against Jerusalem, and the temple was burned. The Jewish historian Josephus gives a detailed eye-witness account. He gives the date of the burning of the temple as 10 Ab. This date was significant to him because it was a date stated in the Bible that the temple was burned by Nebuchadnezzar over six centuries before (Jer. 52:12-13). Josephus stated, "it was the tenth day of the month Lous [Ab], upon which it was formerly burnt by the king of Babylon."^[19]

Other Jewish sources provide more chronological details. Finegan summarizes

Here we get several more clues. The day after the Sabbath would be Sunday and A.D. 70 matches a post-Sabbatical year according to the traditional understanding of the cycle. But for us, the important part is that it occurred in the week of Jehoiarib. Finegan's date of Sun 5 Aug A.D. 70 is on the Julian calendar used by historians, and is the same as the day Sun 3 Aug A.D. 70 on our modern Gregorian calendar, which is used throughout this article.

So now the question is, if we use the correlation we have proposed that Wed 25 Mar 42 B.C. was in the course of Gamul, does that sync up with Sun 3 Aug A.D. 70 being in the course of Jehoiarib?

The answer is in the affirmative, so here we find a second witness of the correctness of our anchor date being Wed 25 Mar 42 B.C. In fact, not one of the other possible starting dates listed in Table 3 would cause Sun 3 Aug A.D. 70 to fall in the course of Jehoiarib. That has at least two implications. First, it strongly implies that we have found the correct date. Secondly, it is consistent with the traditional understanding that the temple priest cycle was unbroken from at least 41 B.C. through A.D. 70.

Conclusion

The conclusions of this article are first, that all of the usually understood features of the Qumran calendar are correct in that it had a 364-day year beginning on a Wednesday, with holy days occurring on fixed days every year. We propose that the calendar was intercalated to keep the feasts at the proper season by inserting an entire extra week after the sixth year of each 7-year count. Moreover, we propose that another entire extra week must have been added about once every 28 years, such that the year would begin on the Wednesday on or after the spring equinox. The Qumran sundial was most likely used for the purpose of knowing when to insert this extra week. By correlating the tables of the full moon in the historically probable period from 50-25 B.C., we deduce that the first day of the first year mentioned in both Calendrical Documents A and B most likely refers to Wed, 25 Mar 42 B.C. Of all plausible dates after 150 B.C. that is the only choice for which the Priest Cycle coincides with that mentioned by Josephus on the date given for the destruction of the temple in A.D. 70.

Notes

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Dr. John C. Lefgren lives in New Jersey and owns his own business. He has a Ph.D. in economics, served as a Foreign Service Officer with the U.S. department of State and was an officer with a major bank in New York. In 1980 his book April Sixth was published and he has maintained an active interest in Church History. He has developed a property in Vermont near the Joseph Smith birthplace Memorial, and a business producing maple syrup.He has five wonderful children and eight lovely grandchildren.

John P. Pratt writes a monthly column for Meridian Magazine giving one L.D.S. perspective on current science.  He has a Ph.D. in astronomy and specializes in religious chronology and ancient calendars. He has authored several articles in the Ensign and professional journals, on his website at www.johnpratt.com, or in a bound volume which is now available. His lovely wife Ruth has written books on family history. They are the parents of five wonderful children.