For New York, Rabbi Moshe Feinstein maintained that the time between שקיעה and צה"כ is 50 mins (corresponding to walking 4 mil), unlike in Europe where it is 72 mins (see here):

... the calculation of the 4 mil between sunset and tzeis. His essential thesis is based on personal empirical observation. Rav Moshe recalled that when he was in Europe, they waited 72 minutes in following the shita of the R”T. Rav Moshe then claims that when he observed the sky in New York, New Jersey, and pashtus, the Catskills, the night sky resembled the 72 minute European night sky after only 50 minutes. Rav Moshe then deduced that the 4 mil of the gm in pesachim are actually 50 minutes in duration.

I have a few questions on this:

1) how does Rav Moshe get to the 50 minutes between שקיעה and צה"כ, is it an average of all times across the year?

2) in reality, there will be occasions where stars come out early or later than 50 minutes. He obviously weighed up the problem of making a blanket 50 minute rule. What are the implications of this?

3) at what latitude can the fluctuation of שקיעה to צה"כ not be averaged in this way?

4) is this method of calculating used anywhere else in the world?

  • 1
    its generally understood that he thought 50 was the longest possible (though he may just not have understood how it fluctuates with the seasons, an issue shared by many even nowadays; the entire teshuva is astoundingly difficult to reconcile with reality or any classical sources, וצע"ג.)
    – Double AA
    May 30, 2019 at 11:48
  • 2
    It's Igrot Moshe 4:62 you can read for yourself hebrewbooks.org/pdfpager.aspx?req=920&st=&pgnum=97
    – Double AA
    May 30, 2019 at 12:02
  • @DoubleAA thanks for the source material. Yes, difficult to understand.
    – bondonk
    May 30, 2019 at 12:29
  • Are there any English summaries or translations of this teshuva?
    – user17319
    Dec 1, 2020 at 14:44
  • 1
    Is this more of a question on Reb Moshe than Rabeinu Tam? Or anyone else who gave a fixed time between sunset and full night?
    – user6591
    Aug 18, 2023 at 10:58

1 Answer 1


I believe that the first three of the questions are based upon an erroneous assumption. For this ruling, it does not seem like Rav Moshe was trying to be precise. He was trying to give a time that, to his satisfaction, is certainly after the stars come out in New York. However, based upon Tosafos in Shabbos 35a and Pesachim 2a, there is no known clear measure of when "the stars" have come out, because it is not know which stars are determinant of nightfall. So Rav Moshe had to make a subjective comparison to 72 minutes after sunset in Russia, and he considered 50 minutes in New York to be dark enough. But just like the 72 minutes is not a single level of darkness, so to 50. It does fluctuate with the time of year and needs to be adjusted for latitude, but that is not the point. The point it to give a convenient time to end Shabbos and make other halachic decisions.

This time is used by many others, according to MyZmanim. It is the 35 minute ending of Shabbos that is generally accepted in Eretz Yisroel.

  • What assumption was erroneous in the question?
    – Double AA
    Nov 30, 2020 at 23:48
  • It seems this answer is based on an erroneous assumption. Some rishonim indeed wrote that they didn't know exactly which three stars are the three medium stars that really define the end of day, but it's not correct that we can't end shabbat upon going outside and seeing three scattered small stars. Indeed that was what all Jews did for centuries till a few hundred years ago in the big cities when they got clocks. (I'm not saying this is what RMF did, since I don't understand him at all.) That's a time you can calculate.
    – Double AA
    Nov 30, 2020 at 23:53
  • The assumption is that Rav Moshe was trying to be precise, as we see from the OP asking about an average, seasonal change, and the latitude for which the ruling was given.
    – Mordechai
    Dec 2, 2020 at 21:23
  • ...and you're correction is that 50 minutes is lav davka? That doesn't seem to be an accurate read of R' Moshe. He really thought 50 minutes was the correct length of time to wait for the situation he was discussing (probably the summer solstice in NYC). He wouldn't have told people 47 minutes was good enough (in that situation, whatever that is)
    – Double AA
    Dec 2, 2020 at 21:24
  • I'm not saying that one can't end Shabbos when he goes out and sees three small stars close together (not scattered, O.C. 293:2). But that is not what Rav Moshe was talking about. He writes that the minhag is to wait 72 minutes, and is not so happy with waiting less than that, but says that at 50 minutes it is as dark as 72 in Russia, so we can't say that one has to wait longer than that. I don't see him saying that it would be impossible to calculate a time that is precise.
    – Mordechai
    Dec 2, 2020 at 21:31

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