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Why does the Jewish leap year always consist of two Adars? Why specifically Adar?

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Summary of our response up to this point: We cited several sources for the law that we only intercalate Adar – including Bavli (Rosh Hashanah 7a and Sanhedrin 12a), Yerushalmi (Sanhedrin 1:2), and Rambam (Hilchot Kiddush Hachodesh 4:1). However, your question is a good one: Why?

Tosafot (Sanhedrin 12a) offers a scriptural reason: to ensure that Adar will remain the twelfth month, as it is referred to in Megillat Esther (3:7).

We noted the reason for any intercalation – the 11-day discrepancy between the lunar and solar years. The lunar year is 354 days, which is the approximate time it takes for 12 new moons to occur. The solar year is 365 days, which is the approximate time it takes for the earth to complete one solar revolution. Thus every several years, an extra month is added to the Jewish lunar year, allowing the lunar and solar years to be in sync again and ensuring that the holidays are celebrated in their correct seasons.

The only logical month to intercalate is Adar. If Nissan or Iyar were intercalated, we would be presented with a problem when counting the omer. We count 49 days starting on the second day of Pesach, Nissan 16, until the omer’s conclusion at Shavuot, the 6th day of Sivan. If we would add a month anywhere between the two, Shavuot would no longer occur in Sivan. While Shavuot is not required to fall on a fixed day, Exodus 19:1 specifically states that the giving of the Torah took place in the third month. As such, Shavuot – when we celebrate being given the Torah – must fall in Sivan.

We examined scriptural mentions of specific dates for other holidays. Parshat Pinchas tells us that Rosh Hashanah is on the first day of the seventh month, Yom Kippur on the tenth day of the seventh month, and Sukkot on the fifteenth day of the seventh month. If we were to intercalate any of the months preceding these festivals, they would not occur in the seventh month as the Torah mandates.

The Gemara (Rosh Hashanah 7a) intimates that we only intercalate right before Nissan because the Torah (Deuteronomy 16:1) requires Passover to fall in the spring. The Rambam writes explicitly that we make two Adars to prevent Passover from sometimes falling in the winter. Pirush Rabbeinu Ovadia adds that in Adar, beit din examines the crops to see whether the wheat has already ripened, a sign that spring has arrived. If it has, there is no need to intercalate that year.

Clearly there are biblical sources to rely on. Why, then, does Tosafot cite a verse in Esther for intercalating Adar? Furthermore, it seems that the verse in Esther refers to a regular year, not a leap year. Otherwise, it would not have referred to Adar as the twelfth month.

I did not find any indication anywhere in Megillat Esther or in the Talmud that it was a leap year. The only source stating so is Rabbi Yosef Grossman in Otzar Erchei HaYahadut, who explains that we celebrate Purim in Adar Sheni because the events occurred during a leap year. However, I cannot find a source for Rabbi Grossman’s contention.

* * * * * Both Adar Rishon and Adar Sheni are properly Adar” in some sense – both in regards to Purim and in regards to the halachot of observing aveilut and yahrzeit.

First, let us discuss aveilut and yahrtzeit so that we can end this discussion on a happy note. If a parent dies in Adar, the yahrzeit the next year should be observed in Adar Rishon (if it’s a leap year). This can be explained based on the time the aveilut commences. A full mourning period is 12 months (even though kaddish is only recited for 11 months as we do not wish to imply that our parents are wicked – see Rema, Orach Chayim 376:4, who notes that judgment of the wicked lasts 12 months). If the yahrzeit was observed in Adar Sheni, the person would wind up mourning for 13 months.


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Rabbi Yaakov Klass, rav of Congregation K’hal Bnei Matisyahu in Flatbush, Brooklyn, is Torah Editor of The Jewish Press. He can be contacted at


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