By Fred Reiss, Ed.D.
WINCHESTER, California – Some begin to think about the Jewish calendar when the High Holidays approach: What at are the upcoming dates for Sukkot, Hanukkah, Passover, and even yahrzeits? But our present ability to easily find current and future Jewish dates did not always exist. At one time, knowledge of the rules structuring the Jewish calendar were a closely held secret, managed by a select group of rabbis of the Judean Sanhedrin known as the Calendar Council.
President of the Sanhedrin Hillel II, in the fourth century, owing to the murderous tactics of the Roman government, which threatened those who developed the calendar and the messengers who brought the news, disseminated the rules for the calculated Jewish calendar, thereby giving Diaspora Jewry the ability to create its own calendars independent of the Holy Land’s official pronouncements. Yet, for most people, even after sixteen centuries, the Jewish calendar remains like an ocean, hiding its riches far beneath the surface. Here are some of her pearls.
The Jewish calendar is a lunisolar calendar because the Torah requires Passover to fall in “Hodesh Ha-Aviv,” the month of spring. If the Jewish calendar were not linked to the seasons, ruled by the Sun, the Jewish calendar would retrogress about 11 days a year, or one season every eight years. The calendar achieves this balance by adding thirty-day month 7 times every 19 years, a scheme learned during the Babylonian captivity and taught by the Greeks. Rosh Hashanah falls early or late every year compared to the secular calendar because these “make-up days” are sometimes added two years and sometimes three years apart, rather than annually.
There really is such a thing as Jewish time, coming in two forms. Religious days begin at sunset, varying from place to place and month-to-month, while Jewish calendar days always begin at 6 PM. Civil time is based on 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute. Jewish time also has 24 hours per day and 60 minutes per hour, but divides each minute into 1,080 parts (chelakim) and each part into 76 moments (regaim). This division of time gives greater precision in calculating the starting day and time for each new month, known as rosh hodesh and the t’kufot, the beginning of the seasons.
Rosh hodesh is celebrated for one day following a twenty-nine-day month and for two days following a thirty-day month—on the thirtieth of the previous month and the first of the new month. The reason is the length of a lunar month is a little more than 29½ days. In twenty-nine-day months, the month is about ½ day too short and in thirty-day months it is larger by about ½ day, which the rabbis say, belongs to the new month. Accordingly, the entire thirtieth day is made part of rosh hodesh and its festivities.
Calendar makers need two facts to create our secular calendar, the day of the week on which New Year’s Day falls and whether the year is common or leap. Jewish calendar makers need three. For example, if Rosh Hashanah falls on Monday in a leap year, then how many days are in the year? It could have 383 or 385 days. So, in addition to New Year’s day-of-the-week and whether the year is common or leap, Jewish calendar makers need to know the character of the year: Is the leap year deficient (383), regular (384), or abundant (385)? The same is true for common years, is the year deficient (353), regular (354), or abundant (355)? The character of the year determines the number of days in the variable-length months of Heshvan and Kislev. Yet, regardless of a year’s character, there are always 177 days from 1 Nisan to 29 Elul, the last day of the year.
The calculated day and time for the New Moon is called, in Hebrew, the molad, from the word “to give birth,” as if the Moon were being born anew. The day of the week for the New Moon is celebrated every month exactly when it is supposed to happen, except for one, Tishri, the start of the Jewish New Year. For religious and year-length reasons, the rabbis can postpone the start of Rosh Hashanah for up to two days. When this happens, the calendar says it’s the first of Tishri, the Moon’s phase says otherwise.
The postponement rules do not allow Rosh Hashanah to fall on either a Sunday, Wednesday, or Friday. So where do the missing seventy-two hours go? The other four days of the week expand, contract, and subsume them. For purposes of constructing a Jewish calendar, 1 Tishri falling on Monday, for example, ranges from forty-five to forty-eight hours long, depending if the year is deficient, regular, or abundant. Under the same conditions, Tuesday ranges from fifteen to twenty-four hours. This is why Rosh Hoshanah is more likely to fall on Monday than Tuesday. The longer the day, the greater the probability of the Moon appearing in it.
Speaking of probability, postponements of Rosh Hashanah occur more than 70 percent of the time. This year’s molad of Tishri falls on a Monday and Rosh Hashanah is not postponed. Next year, however, the molad falls on Friday and Rosh Hashanah is postponed to Saturday.
The ninth-century rabbi and scholar Nachshon ben Zadok, a gaon of Sura, believed the Jewish calendar always repeats every 247 years, meaning the Jewish calendar has 13 unique cycles of 19 years (13 x 19 = 247). He was wrong.
A Jewish nineteen-year cycle is a distinct string of nineteen years. Two cycles are the same only if their string-of-years are the same and in the same order. The old Julian calendar operated with 5 unique cycles repeating every 28 years. The current Gregorian calendar operates with 8 unique cycles repeating every 400 years. (The Gregorian calendar’s second set of 400 years began in 1983). The Jewish calendar has 61 unique nineteen-year cycles repeating every 689,472 years. Only 29 of the 61 cycles have thus far made their first appearance. The last new cycle (number 29) appeared in 1940 (5701) and the next new cycle (number 30) will appear in 2168 (5929). The last, or sixty-first cycle will make its first appearance in 301726 CE.
Each nineteen-year cycle follows a complex pattern of repetitions. Once a cycle appears, it can repeat every 247 years, but not forever, and once that cycle disappears, it takes from 646 to 3,857 years for it to reappear. Since the human lifespan is far less than 247 years, once a nineteen-year cycle has run its course, it will never again be experienced by that person.
Three components define a molad, the day and time for the New Moon: days, hours, and parts. Since there are 7 days in a week, 24 hours in a day, and 1,080 parts per hour, there must be 181,440 different moladot (plural of molad), and since the Jewish calendar repeats every 689,472 years, each molad will repeat 3 or 4 times over the calendar’s recursive period. The earliest a molad can repeat is 117,357 years, so no one will live long enough to experience the same molad twice.
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Fred Reiss, Ed.D. is a retired public and Hebrew school teacher and administrator, and author of several books, including The Jewish Calendar: History and Inner Workings and The Comprehensive Jewish and Civil Calendars, 2001 to 2240. His newest book is 102 Jewish-Themed Word Searches. He may be contacted via fred.reiss@sdjewishworld.com and info@fredreissbooks.com.