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Question: Why does the Jewish leap year always consist of two Adars? And why specifically Adar?

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Answer: Both the Babylonian Talmud (in two places: Rosh Hashana 7a and Sanhedrin 12a) and the Jerusalem Talmud (Sanhedrin 1:2) state that we do not intercalate to create a shenat iybur, a leap year, during any month, save for Adar. The Rambam (Hilchot Kiddush HaChodesh 4:1) codifies this as the halacha. Seemingly, everyone, even the youngest child, is aware of this fact. Nevertheless, your question is a good one: Why?

The Baraita (Sanhedrin ibid., which is the source for our halacha) states: “We do not intercalate the year before Rosh Hashana [in Elul], and if they did intercalate, it is not intercalated; however, in time of duress they may intercalate immediately after Rosh Hashana. Even so, the intercalation is done for the month of Adar.”

Further, not only is the intercalation restricted specifically to the month of Adar but the beit din [in earlier times, when such was the case] may only meet in Adar to decide the intercalation. The Gemara (Sanhedrin ibid.) makes note of this and the unusual exception that was made when Rabbi Akiba was in prison, when the Sages joined him in a session in the prison and proclaimed not one but three [successive] intercalations [i.e. for three different years]. The Gemara explains that even though they sat with him, they met and sat again as a beit din before each of those intercalations [in Adar].

Rashi (ad loc svein ma’avirin”) explains: “Beit din does not sit before Rosh Hashana to delve into the matter and proclaim that this [specific] year be intercalated with two Adars, because there will be forgetfulness of the matter, due to the [long] lapse of time, with the result that they [the people] will come to be careless with chametz [on Passover].”

Tosafot (Sanhedrin 12a, svEin me’averin ela Adar”) offers a scriptural reason for intercalating Adar specifically: “We do not intercalate all [any of] the other months [save for Adar] because of the following verse (Esther 3:7) [In the first month, which is the month of Nissan, in the twelfth year of King Ahasuerus, 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.’ Now, if we are to intercalate one of the other months, then Adar will not be the twelfth month.”

We must note the reason for any intercalation, and that is the discrepancy of the lunar year in contrast to the solar year. Simply put, the lunar year is basically 354 days, which is the approximate time it takes for 12 new moons to occur. On the other hand, the solar year is basically 365 days, which is the approximate time it takes for the earth to complete one solar revolution. There remains an approximate discrepancy of 11 days between the two. Thus, every several years, the cumulative missing days are combined to form an additional month of Adar, delaying the next lunar year from starting again and allowing the lunar and solar years to be in sync again.

It is interesting to note that many other peoples follow a lunar year. The most prominent examples are the Chinese and Muslim calendars. Since Muslims do not have a leap year, their calendar proves to be quite interesting in that their principal month-long fast and feast, Ramadan, occurs throughout the various months of the solar year, depending upon the particular year. Not so the Jewish year, where the lunar year is adjusted with extra months to ensure that the holidays are celebrated in their correct seasons.

(To be continued)


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Rabbi Yaakov Klass is Rav of K’hal Bnei Matisyahu in Flatbush; Torah Editor of The Jewish Press; and Presidium Chairman, Rabbinical Alliance of America/Igud HaRabbonim.