Lunar and Solar Calendar
“And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years” (Genesis 1:14).
As is well known, 12 lunar months aggregate to somewhat shy of a solar year, 354 days as compared to 365 days. How did the Jews adjust the lunar and solar calendar?
CALENDAR RECKONING
In Biblical times it was the responsibility of the Sanhedrin in Jerusalem to determine matters connected with the calendar, and in practice this was done by a council of three men. The month began when the moon was first seen in the evening. The determination that the new moon had actually appeared and the declaration that the new month had thereby begun had to be made by the council just referred to. The testimony of at least two witnesses was required to establish that the new moon had been seen.
In the event that weather obscured the moon the months were alternated at 29 days (“deficient”) and 30 days (“embolismic,” or full). It was also agreed that the year should not have less than five nor more than seven “embolismic” months. The science by which these determinations were made was known as the “fixing of the month” or as the “sanctification of the new moon.”
It was also necessary for the same council of the Sanhedrin to determine when an intercalary month should be added to the year. The rabbis taught that “a year may be intercalated on three grounds: on account of the premature state of the corn crops; or that of the fruit trees; or on account of the lateness of the Tequfah (season). Any two of these reasons can justify intercalation, but not one alone.” Only an Adar could be intercalated. The length of the month (29 or 30 days) was left to the judgment of the council. One chief of the Sanhedrin (Rabbi Simeon ben Gamaliel) wrote, “We beg to inform you that the doves are still tender and the lambs still young, and the grain has not yet ripened. I have considered the matter and thought it advisable to add thirty days to the year.”1 Finegan cites other vivid examples of calendar determination too.2
In the current Jewish calendar the months are tied in closely, but not precisely, with the new moons. Calculation is used, rather than observation. The calendar may be shifted by a day so that certain days will not conflict with sabbaths. The Jewish months and their lengths are given above.
Tishri 1 is the new years day, Rosh Hashanah. The standard year of 354 days is called a “normal ordinary year,” and of 384 days is called a “normal leap year.” Years of only 353 and 383 days are called “deficient years.” Years of 355 and 385 days are called “embolismic years,” or “full years.” (E.g., 385 days constitutes an embolismic leap year.) Calendar information is available several years ahead in common almanacs.
The current Jewish calendar was published by Rabbi Hillel II ca. 359 AD. His calendar could be calculated centuries in advance, which provided a uniform calendar for all Israel in Diaspora (dispersion). In the 4th century Nisan 1 was very nearly the day of the new moon nearest the spring equinox. In the 20th century the calendar has crept so that Nisan 1 is essentially the new moon nearest the 6th day after the spring equinox.3 Calculation of the Jewish calendar is detailed by Zinberg,4 and tables are given for the Gregorian years 1700- 2200 AD (18th to 22nd centuries). [The Gregorian year plus 3761 equals the Jewish year, except for Tishri, Heshvan, Kislev, and sometimes Tebet, which occur on the preceding Gregorian year.]
The Jewish calendar is arranged so that Yom Kippur (Day of Atonement, Tishri 10, itself a sabbath) will not fall on the day preceding or following a sabbath (Saturday), and so that the physical ritual of Hoshana Rabba (Tishri 21) will not fall on the sabbath. Thus Tishri 1 does not fall on Friday, Sunday, or Wednesday. So also, the First Day of Passover (the feast, Nisan 15), occurring 23 weeks and 2 days previously, never falls on Wednesday, Friday, or Monday. Similarly, Nisan 13 (and the sunset beginning of Nisan 14), never falls on Monday, Wednesday, or Saturday, etc.5
ADDENDUM
The American Ephemeris6 summarizes the Jewish calendar in the following manner:
“The ancient Jewish calendar year contained twelve months, each beginning with the first visibility of the crescent Moon as determined by actual observation, and an intercalary month inserted at irregular intervals by repeating the twelfth month. The intercalations were determined by the public authorities, and in the early centuries of the Christian era by the Sanhedrin. The year began with either the spring month Nisan or the autumn month Tishri, according to the country.
“This ancient empirical calendar was replaced, probably during the fourth century of the Christian era, by the fixed calendar which is still used. Dates in the Jewish calendar during the period before it had become a fixed calendar cannot be converted with certainty to dates in the Julian calendar unless contemporary historical records are extant that contain the appropriate information.” 6a
Contrariwise is this single statement on another page: “The Passover was observed on 14 Nisan, and in the ancient Jewish calendar the beginning of this month was determined by observation of the lunar crescent nearest the vernal equinox.”6b
New moon conjunctions have recently been published to high accuracy,7 which makes possible good estimations of the ancient Jewish months (prior to AD 359), but one day or one month errors are possible, except where contemporary calendar information is available. However, none of this influences the present Jewish calendar.
– James Parkinson
- The criteria were practical matters. The lambs needed to be old enough for sacrifice (Exodus 12:5-8), and the firstfruit crops needed to be ripe enough to offer on the first Sunday of the Feast of Weeks (Leviticus 23:10-11).
- Finegan, Jack, Handbook of Biblical Chronology, Princeton University Press, 1964, pages 41-44.
- Thus in the 20th century, about 8 times in 10 Nisan 1 is the new moon nearest the spring equinox, and 7 times in 10 it is the new moon next after the spring equinox. Nisan 1 occurs no earlier than March 12 and no later than April 11, while the spring equinox is within a day of March 21. Note also that calculations of the new moon for America will differ slightly from those for Jerusalem. Jerusalem local time is about 7 hours 20 minutes faster than Eastern Standard Time (e.g., New York).
- Zinberg, George, Jewish Calendar Mystery Dispelled, New York: Vantage Press, 1963. A lucid textbook for the Jewish calendar.
- Note that if the conjunction of the new moon were to determine Nisan 1, the full moon (occurring a mean 14.765 days later) would occur on Nisan 15 or 16. The full moon can occur on Nisan 14 only because Nisan 1 is reckoned according to first visibility, so that the calendar Nisan 1 is displaced a day later.
- Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac, 1961. (a) page 432. (b) page 412.
- Goldstine, Herman H.,”New and Full Moons,” 1001 BC to AD 1651; Philadelphia: American Philosophical Society, 1973. In conjunction with Bryant Tuckerman, “Planetary, Lunar, and Solar Positions,” 601 BC to AD 1, and AD 2 to AD 1649; American Philosophical Society, 1962 and 1964; lunar and solar eclipses may also be determined.