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The latest time for Kiddush Levanah is subject to four layers of debate.
Debate #1: Sanhedrin 41b-42a – Rav Yehuda vs. Naharda’i
The first discussion appears in Sanhedrin 41b-42a. The Gemara cites Rabi Yochanan, who says Kiddush Levanah may be recited only until the moon’s shortcoming is filled. Rashi explains that once the moon is full, it is no longer fitting to say Kiddush Levanah’s Chatimah (conclusion) Baruch Mechadeish Chodashim, Blessed is You Who renews the month.
Rav Yehuda understands Rabi Yochanan to mean until the moon has reached half of its size, which is on the seventh day since the Molad. Neharda’i, though, understands Rabi Yochanan to mean until the moon is full on the sixteenth day.
The Halachah follows the Naharda’i (Rambam Hilchot Brachot 10:17 and Shulchan Aruch Orach Chaim 426:3).
Debate #2: Until the Sixteenth – The Tur vs. the Yad Rama
Naharda’i permits Kiddush Levanah Ad (until) the sixteenth. The Gemara (e.g., Brachot 26b) often notes that the term Ad can mean Ad V’ad Bichlal (up to and including), but also Ad V’Lo Ad Bichlal (up to but not including). The Rishonim debate whether Neharda’i refers to the end of fifteen days from the Molad or to the end of sixteen days from the Molad.
The Tur (Orach Chaim 426) understands the Naharda’i intend Ad V’lo Ad Bichlal, meaning only until the end of fifteen days from the Molad, when the moon begins to wane. The Yad Rama (Sanhedrin 42a), though, understands Naharda’i to mean Ad V’Ad Bichlal and permits Kiddush Levanah until the completion of sixteen days from the Molad. He reasons that the moon’s waning is not apparent on the sixteenth day from the Molad.
The Shulchan Aruch follows the Tur, and the Rama and the Shulchan Aruch’s major commentaries to the Shulchan Aruch do not dissent. However, the Bi’ur Halachah (426:3 s.v. V’Lo Ad Bichlal) records that the Shiyurei Kenesset HaGedola cites Poskim who follow the Yad Rama. The Bi’ur Halachah concludes that several Acharonim rule that if one did not say Kiddush Levanah until the sixteenth day, he should say it without a Berachah. Rav Ovadia Yosef (Teshuvot Yabia Omer 6 Orach Chaim 38 and Yalkut Yosef Orach Chaim 426:37) agrees.
Debate #3: A Full Fifteen Days? Shulchan Aruch vs. The Rama
Although the Shulchan Aruch permits reciting Kiddush Levanah until the end of fifteen days from the Molad, the Rama permits saying Kiddush Levanah only until half of a lunar month has elapsed. According to the Rama, the time for Kiddush Levanah ends approximately five and a half hours earlier than the Shulchan Aruch.
The Halachah calculates a lunar month to be 29 days, 12 hours, and 793 Chalakim (there are 1080 Chalakim per hour). Half of a Halachic lunar month is fourteen days, eighteen hours, and twenty-two minutes after the Molad, which is when the moon begins to wane. Thus, the Rama permits saying Kiddush Levanah only until this time.
The Ashkenazic Resolution
The Bi’ur Halachah (426:3 s.v. V’Lo Ad Bichlal) cites Rav Yaakov Emden (in his Siddur) and the Maharatz Orenshtein (in a Teshuva printed at the end of Siman 426 in the Yeshu’ot Yaakov) who say that even Ashkenazim may follow the Shulchan Aruch. The Bi’ur Halachah concludes that “possibly” one may rely on these views, although in the Mishna Berurah (426:6), the Chafetz Chaim follows the Rama (at least Lechatchila).
The Aruch Hashulchan (Orach Chaim 426:11) rules that even the Rama only Lechatchila requires Kiddush Levanah before half of a lunar month elapses, since the moon’s shrinkage is not noticeable at all until at least fifteen complete days after the Molad has passed. The Chatam Sofer (Orach Chaim 102) agrees with the Aruch Hashulchan.
Rav Hershel Schachter and Rav Mordechai Willig follow the Rama’s stricter view, and Rav Willig does not even permit reciting Kiddush Levanah without a Berachah during the debated time interval. Rav Willig believes that either say Kiddush Levanah with a Berachah or not at all to avoid confusion. He similarly follows Rav Ovadia Yosef (Teshuvot Yabia Omer 8 Orach Chaim 42) and does not permit reciting Kiddush Levanah from the Gemara during questionable intervals. He also does not follow the Bi’ur Halachah’s (426:1 s.v. Asher) possibility that it B’dieved suffices to say Baruch Ata Mechadeish Chodashim without the rest of the Berachah.
The Sephardic Resolution
Rav Ovadia Yosef (Teshuvot Yabia Omer 8 Orach Chaim 42) follows the Shulchan Aruch, despite the Ben Ish Chai (Teshuvot Rav Po’alim 2:38) and the Kaf HaChaim (426:57) following the Rama.
Why do eminent Sephardic Poskim such as the Ben Ish Chai and Kaf HaChaim follow the Rama over the Shulchan Aruch, the Halachic authority of Sephardic Jewry? The answer is that Sephardic Poskim are very concerned for the Rambam’s view (Teshuvot Pe’er HaDor 105) that uttering an unnecessary Berachah is a Torah-level prohibition. Therefore, they typically follow the Chida, who writes (Teshuvot Chayim Sha’al, 2:15) that Sephardic Jews should not follow the Shulchan Aruch when a question of a possible Berachah L’Vatala is at stake.
Sephardic Poskim often say SaBaL (SB”L), an acronym for Safek Brachot L’Hakeil, omit a Berachah when in doubt. Sephardic Poskim even say SB”L to satisfy views that disagree with Maran (Rav Yosef Karo, the Shuchan Aruch’s author).
Rav Ovadia Yosef, who often invokes the SB”L principle even against Maran, sets forth three reasons why this principle does not apply to the end time for Kiddush Levanah. First, the Rama arguably might intend his opinion to be only Lechatchila. Second, some Sephardic Poskim disagree with the Chida and follow Maran even in the case of SB”L. Even the Chida writes that one should not protest a Sephardic Jew following Maran in case of SB”L. Third, Rav Chaim Pelaggi (Teshuvot Chikekei Lev Orach Chaim 4) limits the Chida’s rule to a Mitzvah whose Berachah is in question. However, when reciting the Berachah is the Mitzvah, such as in our Kiddush Levanah case, we do not say SB”L against Maran. One should not miss an opportunity to fulfill a Mitzvah when SB”L runs counter to Maran.
Therefore, Rav Ovadia concludes that one may say Kiddush Levanah until fifteen full days from the Molad elapse.
Debate #4: Yerushalayim or Local Time?
The Molad is determined by its time in Yerushalayim. Consequently, there is considerable debate whether Kiddush Levanah’s beginning time begins 72 hours from the Molad by Jerusalem time (Rav Yosef Eliyahu Henkin, Yagel Ya’akov, letters from Gedolei Yisrael, p. 140, Rav Chaim Kanievsky, ibid., and Rav Hershel Schachter) or the local time (Rav Yonah Merzbach, Alei Yonah, p. 31, noting that this is how the Gedolim, leading Halachic authorities, in pre-war Europe calculated Kiddush Levanah times).
Rav Henkin argues that the time for Kiddush Levanah should be uniform worldwide. However, this reasoning seems questionable, as Tefillah and all other Halachic times are not uniform worldwide. Moreover, the end of Kiddush Levanah time is, as Sanhedrin 41b records, when the moon’s defect has been filled, which varies from locality to locality.
The same question applies to Kiddush Levanah’s end time. For those residing in the United States’ Eastern Time Zone, there is (most of the year) a 7-hour difference between these two views. Rav Mordechai Willig says that one may use local time to mark the end time for Kiddush Levanah, provided that 15 full days from the Molad have not passed according to Jerusalem time. He combines the opinion to follow local time with the Shulchan Aruch’s view to recite Kiddush Levanah until fifteen full days from the Molad.
Rav Meir Gavriel Elbaz, a leading Sephardic authority, says that Sepharadim may recite until fifteen full days from the Molad following the local time. Another leading Sephardic authority, Rav Shmuel Khoshermann, believes that since the matter is subject to dispute, we say SB”L, and recite Kiddush Levanah only at times that satisfy both local (for the start time) and Jerusalem time (for the end). Chabad follows Jerusalem time.
Conclusion – Seize the Earliest Opportunity for Kiddush Levanah
The above discussion should be relevant only in exceptional circumstances. One should habituate oneself to seize the earliest opportunity to fulfill the precious Mitzvah of Kiddush Levanah. As the Mishna Berurah (426:20) writes, “HaZariz Lekadesh Harei Zeh Meshubach, a Zariz (one who acts responsibly and quickly) for Kiddush Levanah is praised.”