Q&A from the Bais HaVaad Halacha Hotline

Light Duty

September 12, 2024

Q What is the deadline for Kiddush Levanah?

A Kiddush Levanah is a bracha on the renewal of the moon, as it concludes, “Baruch…mechadeish chadashim.” As long as the moon is waxing, it is considered new (O.C. 426:3 and Mishnah Brurah). When it begins to wane after the full moon, it is no longer new, so the bracha cannot be recited.

The lunar month (or lunar cycle) represents a complete orbit of the moon around Earth. It takes 29 days, 12 hours, and 793 chalakim (one cheilek= 3⅓ seconds). The moon waxes until the midpoint of the cycle—14 days, 18 hours, and 396.5 chalakim from the molad (“birth” of the new moon)—so that is the deadline (Rama ibid.).

The Shulchan Aruch appears to extend the deadline until 15 full days from the molad. Later Acharonim debate this interpretation, but the Biur Halacha (ibid.) accepts it.

Some poskim (see sources in Piskei Teshuvos ibid. note 213) allow the bracha even beyond 15 days from the molad, provided it is still the 15^th day of the month. (This is possible because Rosh Chodesh must be a full day, so it can begin many hours after the molad.) Consult a rav in such circumstances.

There is a yet more lenient view (cited by Biur Halacha ibid.) that allows Kiddush Levanah on the 16^th, because the waning is not noticeable until 18 hours after the full moon (Shu”t Chasam Sofer O.C. 102). This view is not accepted as halacha, but some suggest that one who has delayed until the 16^th should say the bracha without Hashem’s name (Biur Halacha ibid.). The Chasam Sofer ruled that this opinion may be relied upon bish’as hadchak (if the delay was unavoidable).