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On which night is Kiddush Levana to be said?
A. Motzei Shabbos:
One is to recite Kiddush Levana only on Motzei Shabbos [or Motzei Yom Tov]. [The above time is only with regards to Mitzvah Min Hamuvchar, however from the letter of the law it may be said on any night of the week. Certainly if one did not recite it on Motzei Shabbos, he must recite it during the week.]
If Motzei Shabbos falls past the 10th of the month: One is to only delay saying Kiddush Levana until Motzei Shabbos if Motzei Shabbos falls prior to the 11th of the month. If however Motzei Shabbos falls on the 11th of the month or onwards, then it should be said beforehand [by a weeknight before the 11th]. If it falls on the 10th of the month, one is to delay Kiddush Levana until Motzei Shabbos which is the 10th. However, in a case that the Molad fell out prior to the first day of Rosh Chodesh, in a way that the 10th of the month is the 4th night left to say Kiddush Levana [see previous Halacha for end time of Kiddush Levana], then one is not to delay saying Kiddush Levana until Motzei Shabbos if Motzei Shabbos is the 10th of the month.
If delaying saying Kiddush Levana until Motzei Shabbos will cause one to miss saying it with a Minyan should he say it with a Minyan during the week?
If one is unsure whether there will be a Minyan available for Kiddush Levana on the coming Motzei Shabbos then if he has an opportunity to say it during the week with a Minyan he should do so.
A good omen:
The angelic Maggid of the Beis Yosef stated that one who is able to recite Kiddush Levana on Motzei Shabbos is guaranteed success, while if he is unable to say it on Motzei Shabbos, such as due to clouds, that month will not be successful. [However, some write that these words of the Maggid were only intended to the Beis Yosef and not to the common folk.]
B. Saying Kiddush Levana on Friday night or the night of Yom Tov:
If the last opportunity to say Kiddush Levana is on the night of Shabbos or Yom Tov: If the last opportunity to recite Kiddush Levana falls on Friday night or the night of Yom Tov, it may be recited at that time. [This applies even if Yom Tov falls on Shabbos in which case one would be saying Kiddush Levana on a night which is both Shabbos and Yom Tov. In such a case, one is to say Kiddush Levana immediately at nightfall and only then Daven Maariv.]
If Friday night or the night of Yom Tov is the second to last night to recite Kiddush Levana may one recite it then if the opportunity arrives?
Some Poskim rule it may be recited on Friday night even if there is one more day left for it to be said, as perhaps the moon will not be seen the next night. Other Poskim however rule one is not to say Kiddush Levana on Friday night in such a case.
C. Reciting Kiddush Levana on Motzei Yom Kippur and Motzei Tishe Beav:
Eating and changing clothing before Kiddush Levana on Motzei Yom Kippur: When reciting Kiddush Levana on Motzei Yom Kippur one does not need to eat prior to saying it as one is already in a joyous mood. [However, one should wash his face and switch his shoes beforehand. One is to recite Havdala prior to Kiddush Levana. One recites Kiddush Levana while still wearing a Gartel.]
If eating [or switching shoes] on Motzei Tishe Beav prior to Kiddush Levana will cause one to miss saying it with a Minyan what is he to do?
He is to say Kiddush Levana with the Minyan rather than first eat, as doing so will cause him to miss saying it with the Minyan.
D. Saying Kiddush Levana on the night after a fast:
With exception to the above two mentioned fasts of Yom Kippur and Tishe Beav, one is not to recite Kiddush Levana on the night after a fast, [if the fast falls before the 10th of the month]. One is rather to delay saying Kiddush Levana until a later time. If however it falls on the 9th or 10th or onwards then one may say Kiddush Levana on the night after the fast. One may certainly recite Kiddush Levana on the night after Taanis Esther, as if he does not recite it then the opportunity may be missed.
When at night may Kiddush Levana be said?
 Michaber 426/2; Tur; Miseches Sofrim
Other Poskim: Some Poskim rule one is not to delay saying Kiddush Levana until Motzei Shabbos, as one is not to delay fulfilling a Mitzvah simply in order to fulfill it in a more enhanced way. [Bach; Chayeh Adam 118/14; Maaseh Rav of Gra, Brought in Kaf Hachaim 426/23 and Biur Halacha “Motzei Shabbos”; See M”B 426/20; See also Admur 25/4 that we do not delay a Mitzvah simply to do it in a greater fashion.]
 P”M 426 A”A 2; M”B 426/5 in name of Elya Raba; and so is implied from Teshuvos Harameh 78. [Kaf Hachaim 426/22]
 The reason: As at that time one appears elegant and is wearing nice clothing. [Michaber ibid] Alternatively, some say the reason for saying Kiddush Levana specifically on Motzei Shabbos is because on Motzei Shabbos the Beis Hamikdash was destroyed and the Shechina exiled. Therefore we say Kiddush Levana on Motzei Shabbos which proclaims the return of the Shechina. [Peri Eitz Chaim 19/3; Kaf Hachaim 426/21 in name of Rav Chaim Vital] Alternatively, the reason is because the moon was diminished on Motzei Shabbos. [Tzafnas Paneiach on Rambam Barchos 10]] Alternatively, the reason is because on Motzei Shabbos there are many people found in Shul.
 M”B 426/4; Thus, some Poskim even say that one should not wait until Motzei Shabbos to say it, but should rather say it as soon as he has a chance. [See M”B 426/20 and Poskim in previous footnotes]
 Rama 426/2; Mentioned by Rebbe in Sefer Hasichos Noach 1992 regarding being careful with the Zman of Kiddush Levana; However the Rebbe was seen on numerous occasions to bless the new moon on Motzei Shabbos after the 10th of the month [see Likkut Dinei Rosh Chodesh 12 footnote 32]
 The reason: As perhaps there will be cloudy skies on that Motzei Shabbos and a few days onwards, such as two, three or four cloudy nights [depending on when Motzei Shabbos falls, if on the 11th, 12th, or 13th]. Due to this the moon will not be visible and the time for saying Kiddush Levana will pass. [Rama ibid]
 M”A 426/3; Brought in M”B 426/6; Kaf Hachaim 426/23; Although the Rama writes “When Motzei Shabbos falls before the 10th of the month” nevertheless based on his reason of suspecting for up to four cloudy nights and not more, it is evident that he means to also include the 10th. [M”A ibid]
 This can occur if the Molad fell on the 29th or on the night of the 30th day, and Rosh Chodesh was on the 31st.
 M”A 426/3; As according to the Rama one may only say Kiddush Levana up until 14 days 18 hours and 396.5 chalakim past the Molad, hence one must calculate that Motzei Shabbos is not the 4th to last night to say Kiddush Levana, as in such a case we suspect for four cloudy nights.
 Shaar Hatziyon 426/20
 M”A 426/2 in name of Maggid Meisharim
 Nimukei Orach Chaim 426
 Rama 426/2; Maharil end of Hilchos Shavuos; Rameh Mepuno 78; M”A 426/7; M”B 426/12; Kitzur SH”A 97/12
Other Opinions: Some Poskim rule one may recite Kiddush Levana on Friday night. [Opinion of the Maharash brought in Maharil [the Maharash was the teacher of the Maharil]; Hagahos Maimanis, brought in M”A ibid; Conclusion of Taz 426/1 that so is the main opinion, and so rules Rashba 4/58]
Ruling of Taz: The Taz ibid rules that one may say Kiddush Levana on Friday night and Yom Tov. The Taz concludes his ruling with the following words: “And therefore the Rama did not record this ruling [of not saying Kiddush Levana on Motzei Shabbos which is Yom Tov]” Vetzaruch Iyun Gadol as in truth the Rama ibid explicitly recorded that it is not to be recited. The Chok Yaakov 494/2 asks this question on the Taz and concludes the Taz forgot this ruling of the Rama. However see Peri Megadim 426 M”Z 1 who reads the Taz as follows: “and so is the main ruling, so is the final quote from the Maharil, and the Rama did not bring the opinion of the Maharash which is lenient”. Hence the P”M learns that the Maharil says “and so is the main ruling” and not the Taz. This then leads him to explain that the meaning if the Taz in saying “the Rama did not bring it” is going on the lenient opinion. However Tzaruch Iyun on this explanation of the P”M as the Maharil [as verified after researching his wording in his Sefer] in truth never states “and so is the main opinion”, hence it must be the insertion of the Taz, and the question of the Chok Yaakov therefore remains. After writing the above I found the same claim against the P”M in Kaf Hachaim 426/20.
 M”A 426/7
The reasons behind the prohibition:
- There are many reasons based on Kabala for why one should not recite Kiddush Levana on Friday night or the night of Yom Tov. [M”A 426/7; See Teshuvos Rameh 78; Ridbaz 4/133]
- Some write the reason is because there are Techumin above and one is not to greet the Shechina on Shabbos or Yom Tov outside of the Techum. [Maharil end of Hilchos Shavuos brought in Taz 426/1; Beir Heiytiv 426/5]
- Kiddush Levana is considered a supplication to Hashem, and one is not to pray supplications, such as Tachanun, on Shabbos and Yom Tov. [Maharil end of Hilchos Shavuos; See Shoel Umeishiv Kama 3/51]
- The honor of the Shabbos queen and the holiness of Yom Tov is greater than even greeting the Shechina and hence we do not mix one joy of a Mitzvah with another joy. [Rameh brought in Chok Yaakov ibid; Levush 426; Radbaz 4/1203; See Shoel Umeishiv Kama 3/51]
- Through Kiddush Levana one elevates the level of Malchus, and on Shabbos and Yom Tov Malchus regardless has an elevation. [Magid Meisharim Shir Hashirim, brought in Kaf Hachaim 426/31]
- A simple reason for not doing it then is because the Mitzvah is done with joy and it is thus common to dance, and dancing is forbidden on Shabbos. [See Admur 339/2] Now, although dancing out of joy of a Mitzvah is permitted to be done on Shabbos, as we see is the custom on Simchas Torah, nevertheless that is because one cannot push off the dancing of Simchas Torah to a different date, as opposed to Kiddush Levana which may be delayed to another date. [Shaar Hatziyon 426/12]
- One may come to carry the Siddur into a Reshus Harabim. This is similar to why we don’t say Tashlich on Shabbos. [Sdei Chemed Mareches Rosh Hashanah 2/2; See Minchas Yitzchak 2/20-2]
- One may come to tilt the candles in order to see the words of the Siddur. [Margoliyos Hayam Sanhedrin 42a]
- One does not need the moon light on Shabbos and Yom Tov as one is required to light Shabbos and Yom Tov candles that give light. [Tzafnas Paneiach on Rambam Brachos]
 M”A 426/7 based on Bach who once recited Kiddush Levana on a Friday night that was the last date for it to be recited; So rules also Taz 426/1; Kitzur SH”A 97/12; M”B 426/12
Chabad Custom: In Shemuos Vesippurim [Vol. 1 p. 182] it is recorded from Rav Yaakov Landau OBM, the previous Chief Rabbi of Bnei Braq and the official Rav of the Rebbe Rashab’s courtyard, that he once asked the Rebbe Rashab on Friday night of the 17th of Shevat if he and other members of Anash may still recite Kiddush Levana. The moon had not been seen previously and now it was visible. The Rebbe Rashab replied that he has never seen anyone say it on Friday night and since it is anyways past the date of Kiddush Levana it is to be said the next day.
 P”M 426 A”A 7; See however P”M 426 M”Z 1 who leaves it as a Tzaruch Iyun if one may also say Kiddush Levana on Friday night.
 Kaf Hachaim 426/33 in name of Poskim
 Shaareiy Teshuvah 426/5
 Reb David Openhaimer brought in Shvus Yaakov 3/31
 Shvus Yaakov ibid
 Rama 426/2 [regarding both Yom Kippur and Tishe Beav]; 551/8 [regarding Tishe Beav]; 602/1 [regarding Yom Kippur]
 Rama 426/2; 602/1; Seder Hayom; Levush 602/2 that so is the custom; M”E 602/46; Mishmeres Shalom 41/1; Sefer Haminhagim p. 126 [English]; See Otzer Minhagei Chabad p. 249; omitted from Admur 602 Vetzaruch Iyun!
The reason: It is not to be said before Yom Kippur because one is in a state of pain due to it being a time of forgiveness of sin. [M”A 426/5] Others write as follows: It is not to be said as one is in a state of seriousness due to the days of Judgment and he is thus not in a state of joy which is required for the recital of Kiddush Levana. [M”B 426/9]
Other Opinions: Some Poskim rule that one is specifically to say Kiddush Levana prior to Yom Kippur, as perhaps this merit of saying Kiddush Levana will turn the judgment to the side of good. [Gadol brought in Levush 602/2; Elya Raba 602/7; Beis Meir 426; Biur HaGr”a 602; Chida in Moreh Baetzba 9/283 and other Poskim brought in Kaf Hachaim 426/27; 602/19; M”B 602/10; Biur Halacha 426 “Velo Kodem Yom Hakippurim”; Makor Chaim 602; Nemukei Orach Chaim 602; Alef Lamateh 602/25; See Otzer ibid]
 Rama 426/2; 551/8
The reason: As one is in a state of mourning. [M”A 426/4; M”B 426/8]
 The reason: As on Motzei Yom Kippur one is in a state of joy. [Rama ibid; See 623/14; 624/9 that Motzei Yom Kippur is a Yom Tov.]
 Custom of Arizal brought in Beir Heiytiv 426/4 and 551/25; Arizal in Peri Eitz Chaim 23/1; Kneses Hagedola [brought in M”A 426/6]; Peri Chadash 426/2; Shvus Yaakov 2/11; Elya Raba 551/46; Chida in Moreh Baetzba 8/239; Levushei Serud 551; Ben Ish Chaiy Dvarim 28; Kitzur Shulchan Aruch 124/19; Aruch Hashulchan 551/22; Achronim brought in M”B 426/11; and so is the Chabad custom, and so is the custom of world Jewry. [Kaf Hachaim 551/117; Levushei Serud ibid]
The reason: The reason for saying Kiddush Levana specifically on Motzei Tishe Beav is because that is the time Moshiach was born and the renewal of the moon represents that the Jewish people will return to a renewed state. [Kaf Hachaim 426/29 in name of Rav Chaim Vital]
Other Opinions-Ruling of Rama: The Rama [426/2] rules one is not to recite Kiddush Levana on Motzei Tishe Beav, or the Motzei of any fast. The reason for this is because one is not in a state of joy after a fast. [M”B 426/10] In 551/8 the Rama writes one is to say Kiddush Levana after Tishe Beav. The Taz [551/8] explains that the Rama does not mean to say one is to say it immediately after Tishe Beav, as this would be contradictory to his earlier ruling in 426/2. Rather he means that one is to say it the next day. The Kaf Hachaim [551/117] gives an alternative explanation of the Rama that here the Rama is stating the custom, that the custom is to recite Kiddush Levana on Motzei Tishe Beav while earlier in 426/2 the Rama was ruled based on the letter of the law. Aruch Hashulchan 551/22 rules unlike Rama for the reason that one may not receive another opportunity to say Kiddush Levana if he were to delay it pass Tishe Beav, as well as that one may not delay fulfilling a Mitzvah that he was given the opportunity to fulfill.
 M”B 426/11
 Chayeh Adam 118/15; M”B ibid
 Peri Chadash 426/2; P”M 554 A”A 1; M”B ibid
 M”B 426/11
 Chayeh Adam 118/15; M”B ibid
Other opinions: Some Poskim rule one is to eat beforehand. [Mateh Efraim 624/4]
 Luach Kolel Chabad
 Luach Kolel Chabad; Piskeiy Teshuvos 624/1; The Rebbe switched his shoes beforehand. [Reply of Rabbi Groner in correspondence]
Other customs: Many are accustomed to recite it immediately after Davening, even prior to changing shoes. [Nitei Gavriel Yom Kippur 66/15 footnote 23]
 Sefer Haminhagim p. 126 [English]; Likkut Dinei Rosh Chodesh 12/13
The reason: Perhaps this is because Havdala is more Tadir. [see Poskim in 681 regarding Chanukah]
 Sefer Haminhagim p. 126
 Shaar Hatziyon 426/9 based on Elya Raba; Mateh Efraim 624/4
 Rama 426/2
Other Opinions: Some Poskim rule that the custom is to allow saying Kiddush Levana on the night after a fast. [Opinion brought in M”A 426/6 and Achronim brought in M”B 426/11 that one may say Kiddush Levana on the night after a fast.]
 Shaar Hatziyon 426/8; Meaning if the night after the fast is the 10th of the month then one should not push it off. Vetzaruch Iyun
 And hence the eve after the fast is the 10th of the month or onwards.
 Shaar Hatziyon 426/8 writes “the 9th or the 10th” Vetzaruch Iyun as if he will not delay if it falls on the 9th why does he mention the 10th. Perhaps then the explanation is that it depends on how cloudy one’s area is. This perhaps would explain why the M”A 426/6 did not mention any specific date and simply stated if the time will pass one is not to delay.
 M”A 426/6 as explained in Shaar Hatziyon 426/8; The M”A 426/6 rules that if the time is passing one is not to delay it. He however does not mention how many days must be left. In the Shaar Hatziyon the M”B concludes that if the fast is past the 9th of the month then one should not delay it.
 Taz 426/2
 M”A 426/6
 The reason: As Berov Am Hadras Melech. [M”A ibid]
 Shaar Hatziyon ibid
 Ben Ish Chaiy Vayikra 23; Kaf Hachaim 426/15; See Igros Kodesh of Rebbe Rashab 2/543 that he said Kiddush Levana after midnight
 M”B 426/2