The full moon occurs at the halfway point of the lunar cycle (which according to halacha is on average 29 days, 12 hours and 793 chalakim, see here). The Shulchan Aruch (OC 426:3) says one can say Kiddush Levana until but not including 16 days from the Molad (the new moon, the start of the lunar cycle). The Rema says it can be said until the halfway point of the lunar cycle mentioned above, since at that point the moon is full and begins to wane (on a side point the Aruch Hashulchan says the SA agrees he just didn't bother writing precisely). This Rema is based on Teshuvos Maharil # 19.

My question is as follows. The continuation of that teshuva mentions that if a Lunar Eclipse occurs before this cut off time, then one can no longer say Kiddush Levana. This is because a Lunar Eclipse only occurs when the moon is full. One therefore cannot say Kiddush Levana even if the halfway point of the above cycle hasn't occured. This can happen since it's only an average.

The Beis Yosef quotes this part of the teshuva, but he doesn't bring it down in the SA. The Rema doesn't mention it, nor the Mishnah Berurah or Aruch Hashulchan. Is there anyone who rules in accordance with this teshuva? It logically makes sense to me, and I find it curious none one (I know of) says it should be followed.

  • This is indeed the way we do it in our shul. I have heard it spoken of in a shiur and I believe other rabbanim in Baltimore follow this psak. I do not have external sources, so I am leaving it a comment. Outside sources that I have seen were not halachic authorities. – sabbahillel Nov 16 '17 at 5:20
  • I'm surprised it's relevant/frequent enough for your shul to have an official position on the matter – robev Nov 16 '17 at 13:25
  • It is not that it is an official position, but that since it is a situation that comes up, we learned about what to do. It may happen only once, but for those who are interested in learning the halachos of the chodesh, it is something to learn about even if it is only theoretical. – sabbahillel Nov 16 '17 at 16:14

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