Why is there a custom to say "Kiddush Levana" (Moon Blessing) on Motsaei Tisha Be'av?

Question

Why do some have the custom to say Kiddush (Birkat) Levana on Motsaei Tisha Ba'Av and not on the Shabbat after it (or before it)? After all, it is customary to say Kiddush Levana on Motsaei Shabbat is said out of joy and in nice clothes. And we don't wear nice clothes on Tisha Be'Av? And if the temple is not built, then there is no joy either? And besides, the people are hungry after the fast. If so, why did they use to say precisely on Motsaei Tisha Be'Av?

Answer 1

Why not say kiddush levanah on the motzaei shabbat before tish'ah be-av?

Rema Orach Chaim 426:2 (quoting Maharil) writes that one does not recite kiddush levanah before tishah be-av. Mishnah Berurah 8 explains that this is because before tish'ah be-av one is in the midst of mourning.

(However, it is worth noting the custom recorded in Aruch HaShulchan 551:22 to ignore this Maharil and rather to recite kiddush levanah before tish'ah be-av -- as we don't want to delay a mitzvah, and out of concern for subsequent cloudy nights. That was also the practice of the Vilna Gaon (Maaseh Rav 159).)

OK. So why not say it on the motzaei shabbat after tish'ah be-av?

Kiddush levanah can only be said until the moon becomes full (approximately on the fifteenth of the month; see Shulchan Aruch Orach Chaim 426:3.) Thus when the ninth of Av falls on shabbat or Sunday, one cannot wait until the following motzaei shabbat (the night of 16th or 17th of Av) as it is very likely to be too late.

Even when tish'ah be'av falls on Tuesday, one would not want to wait until motzaei shabbat (the night of the 14th of Av) in case there are a few cloudy nights and he ends up missing the opportunity. (See Rema Orach Chaim 426:2, quoting the Terumat HaDeshen, that in any month one does not wait to say kiddush levanah on motzaei shabbat past the tenth of the month.)

When tish'ah be-av falls on Thursday, Rema in Darchei Moshe (quoted in Mishnah Berurah 10) indeed rules that one waits to say kiddush levanah on the following motzaei shabbat (the night of the twelfth of Av), notwithstanding the general rule of not waiting past the tenth quoted in the previous paragraph.

So kiddush levanah in Av is generally not going to be done on motzaei shabbat. But why do it on motzaei tish'ah be-av?

This is a great question. Rema Orach Chaim 426:2 specifically says not to recite kiddush levanah on motzaei tish'ah be'av, and instead do it on a subsequent night, although not (in general) waiting for motzaei shabbat. Levush ibid. :4 writes such as well. Mishnah Berurah 10 explains (as you note in your question) that motzaei tish'ah be'av is not a time of joy. (Presumably, Rema would also instruct you to put on nice clothes when you recite kiddush levanah on a weeknight following motzaei tish'ah be-av, as he rules in general regarding reciting kiddush levanah on a weeknight (462:2).)

However, as you observe, many people do not follow this ruling of Rema, and do recite kiddush levanah on motzaei tish'ah be'av.

Mishnah Berurah 11 quotes "the acharonim" as permitting this practice, but notes the incongruity of reciting kiddush levanah while still fasting and not wearing shoes. He therefore writes that one should eat something and put on one's shoes before reciting kiddush levanah on motzaei tish'ah be'av. (In Sha'ar HaTziyun 9, he points out that if waiting to eat will cause one to miss reciting kiddush levanah with the community, it is better to recite it with them before eating, due to the principle of berov am hadrat melech.)

If we rule against the Rema, then kiddush levanah in Av can be done on motzaei tish'ah be-av. Is there a specific reason to do so, rather than waiting until a later night?

Baer Heitev to Orach Chaim 551:8 notes the Arizal's directive to specifically recite kiddush levanah on motzaei tisha'ah be-av, as it is the time of Mashiach's birth, which ties in thematically with the rebirth of the moon.

On a more practical level, we pointed out that one is not supposed to wait past the tenth of the month to recite kiddush levanah, out of concern for cloudy nights. That being the case, once we rule that it is permitted to recite kiddush levanah on motzaei tisha'ah be-av (the tenth of Av), my assumption is that one should specifically do so, to minimize the chances of missing it (as well as the general principle of doing mitzvot as speedily as possible). See Kenesset HaGedolah, Orach Chaim 426 who invokes the worry about cloudy nights as a reason to not push off reciting kiddush levanah from motzaei tish'ah be-av.

Further, in many communities, I imagine that arvit on motzaei tish'ah be-av attracts larger crowds than a regular weeknight arvit. Therefore, it makes sense to me for those communities to specifically recite kiddush levanah then, to increase the chances of more members of the community reciting it that month.