I would appreciate someone directing me to a source that states/indicates/suggests whether the visibility of the new moon outside the Land of Israel may be used to begin the Jewish month in that region. Basically, if the Calendar had not been pre-calculated, what would keep an observant Jew living in Egypt or Spain or Cleveland from using the local new moon to determine when the new month begins? (Another way of stating this question is this: Is there anything in the Tanakh or any Rabbinic text that says the new moon that starts our Jewish months must be the new moon observed in Israel?)

  • 1
    If I'm not mistaken, the rule was that it needed to be declared by the Sanhedrin (ie., not a Beith Din of three).
    – Seth J
    Commented Jan 31, 2013 at 20:23
  • @SethJ I suppose that's logically a true statement, but not a very useful one: he.wikisource.org/wiki/…
    – Double AA
    Commented Jan 31, 2013 at 20:24
  • @doubleaa,, I wasn't attempting to answer the question.
    – Seth J
    Commented Feb 1, 2013 at 0:17
  • @SethJ Did you read my link? 3 is good enough for Kiddush haChodesh and bedieved even for 'Ibur Shanah.
    – Double AA
    Commented Feb 1, 2013 at 3:22
  • @doubleaa,, I saw. I was obviously mistaken. But I'm still pretty sure it was done only centrally, not by each locality.
    – Seth J
    Commented Feb 1, 2013 at 4:32

1 Answer 1


The Mishna in Rosh haShana (3:1) states that even if all the Jews and the Beit Din saw the new moon, but didn't manage to declare the new month before the end of the day, then the (previous) month is 'full' (ie has 30 days and the new month would begin the next day).

In other words, Rosh Chodesh is set by declaration of the people via Beit Din, not by when the new moon was seen. So even if you saw the new moon in Cleveland, you wouldn't know if anyone had testified to Beit Din and that they declared the new moon.

A few other points: the Talmud relates (Rosh haShana 25a) that the power is entirely in the hands of the Beit Din to the extent that even if Beit Din declares Rosh Chodesh on the wrong day on purpose, the declaration is valid and the new month takes effect.

The Talmud in Brachot (63a) relates that certain Rabbis declared the new moon while not in Israel; however they only did so because there were no other Rabbis in Israel as qualified as they were to make the declaration. The Rambam writes in his Sefer haMitzvot (Aseh 153) that the current calendar only works because there exist currently Jews that live in Israel. Were to be (chas veshalom) that no Beit Din was left in Israel, nor any Beit Din that received Semicha in Israel but has since moved to the Diaspora, then the current calendar would somehow stop. The Ramban there argues on this, but all agree that while the formal declaration of a new month could happen in theory outside of Israel, it rarely did. Israel is clearly the focal point of the whole operation.

  • Is the following statement intended to suggest that if all those other conditions were met, in theory the new moon could be declared from the sighting of the new moon in Spain? ("The Ramban there argues on this, but all agree that while the formal declaration of a new month could happen in theory outside of Israel, it rarely did. Israel is clearly the focal point of the whole operation.") Commented Jan 31, 2013 at 20:52
  • @ABlueThread The Ramban there argues with the Rambam who said the months are currently being sanctified each month by the 'community in Israel'. The Ramban holds that when the fixed calendar was established by Hillel II, he already declared them all sanctified. So no need for any current situation in Israel to maintain it. I would have to do more research regarding the Ramban's general position on Diaspora-based declarations of the new moon.
    – Double AA
    Commented Jan 31, 2013 at 21:16
  • Thank you. I recently learned (much to my surprise) that some Karaite religious leaders in Israel (apparently) hold the view that nothing in the Peshat mandates that the new moon be the new moon sighted in Israel. According to this view, one could declare the new month based on the sighting in Egypt. (But I haven't spoken to them directly to test the limits of this view.) On one hand, we in the diaspora observe our Sabbath based on the local sunset. On the other hand, even Karaites in the Diaspora recognize that the Abib/Aviv must be found in the Land of Israel in order to begin the new year. Commented Jan 31, 2013 at 21:29
  • Ramban disputes this opinion of the Rambam.
    – b a
    Commented Jan 31, 2013 at 22:14
  • @ba Didn't I mention that? Or are you referring to something else?
    – Double AA
    Commented Jan 31, 2013 at 22:19

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .