Which month is a leap month? T Rosh Hashana 7

Everybody knows the old joke that either the High Holidays are early or late, but never on time because they can either begin as early as the very end of August or at the very end of September/beginning of October. This is based on the fact that the secular calendar is a solar calendar and the Hebrew aka Jewish calendar is a lunar calendar. The solar calendar is 365 days long and the loaner calendar is only 354 days long. Every four years in a leap year February has 29 days instead of the usual 28. The Jewish calendar also has leap years; however, we add a whole extra month seven times in a 19 year cycle, the years 3, 6, 8, 11, 14, 17, and 19 are the leap years (13-months) to make sure that Passover, the holiday of springtime actually falls in the spring. If we did not make these adjustments, we would sometimes celebrate Passover in the dead of winter! By the way, the Muslims do not inter-calculate their lunar calendar; consequently, the dates of Ramadan moves throughout the solar calendar.

You may know that a Jewish leap year has two Adars. TB Rosh Hashana 7 explains why the first Adar is the extra month added!

“It was taught in the baraita: And on the first of Nisan is the New Year for leap years. The Gemara asks: Do we really count leap years from Nisan? But isn’t it taught in a baraita: The court may not declare a leap year before Rosh HaShana, and if they did declare a leap year before Rosh HaShana, the declaration is not valid and it is not considered a leap year. But due to pressing circumstances, e.g., religious persecution, it may be declared immediately after Rosh HaShana. At that time, the Sages may declare that the coming year will be a leap year in accordance with their calculations. Even so, the additional month added to the leap year can be only a second Adar. In what sense, then, is Nisan the New Year for leap years?

“Naḥman bar Yitzḥak said: What is meant here by leap years? It means the end of the leap year. Once the month of Nisan has arrived, the previous year can no longer be declared a leap year, as we learned in a mishna: They, Rabbi Yehoshua and Rabbi Papeyyas, testified that the court may declare a leap year all through the month of Adar, as there were Sages who said: A year may be declared a leap year only until Purim, and if the decision to declare a leap year was not made before Purim, the year can no longer be declared a leap year.

“The Gemara explains the dispute: What is the rationale of the one who said that a leap year can be declared only until Purim? It is since the Master said: One asks about the halakhot of Passover thirty days before Passover. Immediately following Purim, on the fifteenth of Adar, people already began to immerse themselves in the halakhot of Passover, which occurs on the fifteenth of Nisan. Were the court to declare a leap year after Purim, the festival of Passover would then be delayed for another month. In that case, there is concern that people will come to demean the prohibition against leavened bread and not observe Passover on its new date in the proper manner.

“And the other Sages, Rabbi Yehoshua and Rabbi Papeyyas, who are not concerned about this, what do they say? They say that people know that a leap year is dependent on the calculation, and they will assume that the Sages did not complete the calculation until now, after Purim. Since this is a matter of common knowledge, there is no concern that declaring a leap year at that late time will lead to a disregard of the halakhot of Passover.” (Sefaria.org translation)

“How does a leap year effect the observance of a yahrzeit?” is a common question I’m asked. If a person dies in Adar I, the yahrzeit is observed in Adar I in a leap year. Although some will observed the date in both Adar I and in Adar II. If the year is a regular year, the date of the yahrzeit is observed in Adar. If a person dies in Adar II in a leap year, the yahrzeit is observed in Adar II. Although some will observed the date in both Adar I and in Adar II. If the year is a regular year, the yahrzeit is observed in Adar.