37 Rosh Hashana 20a

But if you say that the Adar immediately preceding Nisan is always short, why should they desecrate Shabbat? The court can calculate the time of the New Moon without witnesses. The Gemara answers: Because it is a mitzva to sanctify the New Moon on the basis of the testimony of witnesses who actually saw the new moon and not rely on calculations or established practices. Some say that Rav Naḥman said: We, too, learn in a mishna: Witnesses who saw the new moon may desecrate Shabbat to establish the New Moon for two months, for the month of Nisan and for the month of Tishrei. Granted, if you say that the Adar immediately preceding Nisan is always short, due to that reason the witnesses may desecrate Shabbat, because it is a mitzva to sanctify the month on the basis of the testimony of witnesses who actually saw the new moon. But if you say that the Adar immediately preceding Nisan is sometimes full and sometimes short, and there is no regularity to it, why should the witnesses desecrate Shabbat? Have the court add an extra day to the month now, since it can decide whether the thirtieth day or the thirty-first day is the beginning of the new month, and let the members of the court sanctify the next day as the New Moon. The Gemara rejects this argument: If the thirtieth of Adar falls on Shabbat, this is indeed what is done. The witnesses are not permitted to desecrate Shabbat. Rather, the month is made full and the next day is sanctified as the New Moon. Here we are dealing with a case where the thirty-first of Adar falls on Shabbat, and so the sanctification of the New Moon cannot be pushed off to the next day, as a month cannot be longer than thirty days. In that case, the witnesses may desecrate Shabbat because it is a mitzva to sanctify the month based on testimony of witnesses who actually saw the new moon. Rav Kahana raised an objection from the continuation of the mishna, which teaches: When the Temple was standing, the witnesses would desecrate Shabbat for establishing the New Moon even for all the months, in order to rectify the offering of the New Moon, i.e., ensure that it is at the proper time. From the fact that the reason that the witnesses are permitted to desecrate Shabbat for all the other months is not because it is a mitzva to sanctify the month based on testimony of witnesses who saw the new moon, the implication is that with regard to Nisan and Tishrei as well, the witnesses are permitted to desecrate Shabbat for another reason and not because it is a mitzva to sanctify the month based on the testimony of witnesses who saw the new moon. Granted, if you say that Adar is sometimes full and sometimes short, due to that reason the witnesses may desecrate Shabbat. But if you say that Adar is always short, why should they desecrate Shabbat? The court knows in advance when will be the New Moon of Nisan. The Gemara concludes: This is indeed a conclusive refutation to the proof brought by Rav Naḥman. § It is related that when Ulla came from Eretz Yisrael to Babylonia, he said: This year they added an extra day to the month of Elul. Ulla continued and said: Do our Babylonian colleagues understand what benefit we did for them? We pushed off Rosh HaShana for a day, so that the Festival would not occur adjacent to Shabbat. The Gemara asks: What is the benefit in having a weekday between Shabbat and a Festival? Ulla said: Due to the vegetables that would not be picked for two days and those picked beforehand that would no longer be fresh. Rabbi Aḥa bar Ḥanina said: Due to the dead who would not be buried for two days and consequently would begin to decompose. The Gemara asks: What is the practical difference between these two concerns? The Gemara answers: The practical difference between them is in the case where Yom Kippur occurs directly after Shabbat. According to the one who said that the reason is due to the dead that would go unburied for two days, the court adds an extra day to Elul so that Yom Kippur will not occur on Sunday. But according to the one who said that the reason is due to the vegetables that would not be fresh, there is no need to add an extra day to Elul. When would he require the vegetables? Only in the evening following Yom Kippur; and if Yom Kippur falls on Sunday, he can go out in the evening after the fast and bring fresh vegetables. The Gemara asks: But according to the one who says that the reason is due to vegetables, the court should still make Elul full due to the dead, as this is also an important consideration. Rather, the practical difference between them is with regard to the case where the Festival of Rosh HaShana occurs adjacent to Shabbat, either before it or after it. According to the one who said that the reason is due to the vegetables that would wither, the court adds an extra day to Elul. But according to the one who said that the reason is due to the dead that would go unburied, there is no reason to make Elul full, because on a Festival it is possible to arrange that the dead be buried by gentiles. The Gemara asks: But according to the one who said that the reason is due to the dead, the court should still add an extra day to Elul due to the vegetables. The Gemara answers: According to him this is not an important consideration, because it is possible to soak the withered vegetables in hot water and thereby restore their freshness. The Gemara asks: If so, what is different about those who live in Babylonia and those who live in Eretz Yisrael? Why did Ulla specifically say that adding an extra day to Elul was beneficial to us, in Babylonia; it was beneficial to them as well. The Gemara answers: For us in Babylonia the weather is very hot, and so vegetables wither and corpses decompose quickly. But for them in Eretz Yisrael, the weather is not as hot, and vegetables and corpses can be kept for two days. § It was taught above that for various reasons a month can have an extra day added, even if the new moon was seen on the night before the thirtieth. The Gemara challenges this assumption: Is that so? But didn’t Rabba bar Shmuel teach in a baraita: One might have thought that just as the court adds an extra month to a year for some pressing communal need, so too, the court adds an extra day to a month for some similar need. Therefore, the verse states: “This month shall be to you the beginning of months” (Exodus 12:2). This teaches that when there is a moon like this, see it and sanctify the month. When the new moon is seen, the month must be sanctified without delay. Rava said: This is not difficult: Here it is speaking of adding an extra day to the month, although the new moon was seen on the thirtieth, which is permitted; whereas there it is speaking of sanctifying the month on the thirtieth, although the new moon was not yet seen, which is prohibited. And this is what the baraita is saying: One might have thought that just as the court adds to a year or a month for some pressing communal need, so too, a month can be sanctified early on the thirtieth even without seeing the new moon. Therefore, the verse states: “This month shall be to you the beginning of months,” which teaches: Only when the moon appears like this, see it and sanctify the month, but not before. The Gemara comments that this is like that which Rabbi Yehoshua ben Levi said: The court may intimidate witnesses through rigorous and confusing examination, so that they will give inadmissible testimony about the new moon that was seen at its due time, the thirtieth of the month. This is so that the court can add an extra day to it, and the New Moon will be sanctified on the thirty-first day. But the court may not intimidate witnesses into giving testimony about the new moon that was not seen on its due time, in order to sanctify the New Moon early, on the thirtieth. The Gemara asks: Is that so? But didn’t Rabbi Yehuda Nesia, who was the Nasi of the Sanhedrin, send a message to Rabbi Ami: Be aware that all the days of Rabbi Yoḥanan he would teach us that witnesses may be intimidated into giving testimony about the new moon that was not seen in its due time. This was done in order that the new month may be sanctified early, already on the thirtieth. Although the witnesses did not see the moon, they may say: We saw it. Abaye said: This is not difficult: This ruling is referring to Nisan and Tishrei, which may be sanctified early in order to set the Festivals that occur in those months; that ruling is referring to the other months, which may not be sanctified early, even for some other pressing need. Rava said: That which Rabba bar Shmuel taught, that the court may not lengthen or shorten the months for reason of communal need, follows the opinion of Aḥerim, as it is taught in a baraita: Aḥerim say: The difference between the festival of Shavuot of one year and the festival of Shavuot of the following year, and similarly, between Rosh HaShana of one year and Rosh HaShana of the following year, is only four days of the week. There are 354 days in a lunar year, which are divided into twelve alternating months, six months that are thirty days long and six months that are twenty-nine days long. Therefore, every year is fifty weeks and four days long. And if it was a leap year, in which case the year is comprised of 383 days, or fifty-four weeks and five days, there is a difference of five days between them. Rav Dimi from Neharde’a taught the baraita in the opposite manner: The court may intimidate the witnesses into giving testimony about the new moon that was not seen in its due time in order that the new month may be sanctified early, already on the thirtieth. But the court may not intimidate witnesses so that they do not give acceptable testimony about the new moon that was seen in its due time, in order to add an extra day to the old month, so that the New Moon is sanctified on the thirty-first. The Gemara asks: What is the reason for Rav Dimi’s opinion? Intimidating witnesses into testifying about something that they did not see is worse than intimidating them to withhold testimony about something that they did see.