Question: Why is there an extra month in the Jewish calendar every few years? And who decides whether a particular year should be a leap year or not?
Name Withheld
Toronto, Ontario
Answer: The Jewish calendar consists of 12 lunar months. A lunar month is the time it takes for the moon to go through a full cycle of its phases, which is approximately 29 and a half days; thus, a 12-month year has 354 days.
It takes the earth approximately 365 and one-quarter days to complete one revolution around the sun. Thus, there is a difference of about 11 days between the solar and lunar years, and if there were no leap years, the same Hebrew date would fall 11 days earlier every year until a date that was once in the summer would, after a number of years, be in the winter. The 15th of Nissan, for example – the first day of Pesach – would eventually wind up being in the winter, fall, or summer, even though the Torah specifically states that Pesach is supposed to be a spring festival. Leap years are therefore necessary.
In fact, the Torah (Deuteronomy 16:1) specifically commands us to regulate the calendar: “Shemor et chodesh ha’aviv – You shall observe the month of springtime.” The Talmud (Sanhedrin 13a) explains that this imperative requires us to ensure that Nissan always fall in the spring. That’s why we add extra days to the calendar every few years.
The Talmud discusses at length (ibid., 11a and ff.) when it’s appropriate to add these extra days and concludes that spring is the proper season due to the verse quoted above (Deuteronomy 16:1). Commenting on this verse, Rashi writes that we’re supposed to ensure that spring doesn’t start later than the time for offering the Omer, which is the 16th of Nissan. We accomplish this task by adding an extra month between Adar and Nissan if necessary.
The Talmud leaves open the question of whether we should add a few days each year or add one month every few years. The Rambam (Hilchot Kiddush HaChodesh 4:1) rules that we add an extra month. The Ra’avad, in his commentary on the Rambam’s Hilchot Kiddush HaChodesh, notes that the word “ibbur – intercalation” also means pregnancy since the year becomes “pregnant” with an extra month through intercalation.
Based on the Talmud’s discussion, the Rambam writes that we only add a month between Adar and Nissan so that the year has two Adars (Adar I and Adar II).
Tosafot (Sanhedrin 12a, sv “Ein me’averin ela Adar”) offers a scriptural reason for specifically adding an extra Adar: Megillat Esther (3:7) states, “Bachodesh harishon hu chodesh Nissan bishe’nat shteim esreh l’melech Achashveirosh hipil pur, hu hagoral lifnei Haman, miyom l’yom u’me’chodesh l’chodesh shneim asar hu chodesh Adar – In the first month, which is the month of Nissan, in the twelfth year of King Akhasuerus, they cast pur, that is the lot, before Haman from day to day, from month to month, to the twelfth month, which is the month of Adar.” If we added an extra month in the calendar anywhere other than after Adar, Adar would not be the twelfth month.
The Rambam writes that beit din decides whether or not to establish a leap year (see also the Tur, Orach Chayim 427-428).
(To be continued)