More Discussions for this daf
1. Molad and Rashi on daf 20b. 2. 24 Hours of Moon Non-visibility 3. Query on the Review Questions
4. Chatzos?? 5. Magid ha'Raki'a 6. Elul
7. Rosh Hashanah on Sunday 8. 18 hours before the molad in jerusalem 9. witnesses
10. Yarkaya 11. About Kidush Hachodesh 12. How Could Ula Testify?
DAF DISCUSSIONS - ROSH HASHANAH 20

Tzvi Goldman asks:

Hello,

I saw the following explanation of this sugya cited from the Daf Yomi Advancement Forum:

If the molad is at around noon in EY, the new moon will be visible at sunset (6 hours later) for those in EY, but the old moon was visible for those in EY only 18 hours earlier, at the previous sunset. In Bavel, the new moon will be visible only 18 hours later, at the next sunrise, but the old moon was visible 6 hours earlier, at sunrise.

My question is as follows: I was under the impression that one would not be able to see the new moon at sunrise, since the sun rises before the new moon. Similarly, one would not be able to see the old moon at sunset, since the moon sets before the sun. Thus, the old moon should have been visible in EY only 30 hours after the molad (at sunrise of the previous day), and the new moon should be visible in Bavel only 30 hours after the molad (at sunset of the next day).

Any "enlightenment", be it large or small (pun intended), would be greatly appreciated.

I am fine with a response in Hebrew, if that is easier.

Tzvi Goldman, Ramat Beit Shemesh

The Kollel replies:

(a) Let me first point out that I am not sure where you found the quote from our site that was cited. (We have 16 different types of study material on each Daf, and I am not sure that your citation appears in any of the recent versions of our study material.)

In any case, let us correct the quote to read, "If the molad is a bit before noon in EY," (instead of "around noon"), to be more accurate.

(b) As for your question - I believe that you have things right. Before the Molad (i.e. the "old" moon), the moon is to the west of the sun and therefore rises and sets before the sun. (All celestial bodies travel from east to west, and if the moon is further west it will rise and set first). After the Molad (i.e. the "new" moon), the moon has "caught up" with the sun and is now east of the sun, so that it rises and sets after the sun.

This seems to conform well to we you quoted: The "new" moon will be visible at sunset (i.e. until shortly after sunset) for those in EY. In Bavel, the old moon was visible 6 hours earlier, at sunrise (i.e. it rose slightly before the sun, and was visible before the rising of the sun).

Please clarify what was unclear to you about what the Kollel wrote.

I am including below a quote from our Insights to the Daf on this Daf which is pertinent to what you wrote.

Best regards,

Mordecai Kornfeld

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From Insights to the Daf, Rosh Hashanah 20 3:(a):3

Since in Bavel the Molad is half an hour after Chatzos, the moon will not be visible that evening (6 hours will not have passed from the Molad before moonset, which is approximately 6:12 that evening, about twelve minutes after sunset). However, the Molad did occur more than 6 hours from sunrise that morning. Therefore, that morning the old moon was visible in the east, right before sunrise (i.e., to the immediate east of the sun) when the moon was three degrees away from the sun.

The first time the people in Bavel will be able to see the new moon after the Molad is approximately 18 hours after the Molad -- that is, when it rises again the morning after the Molad. This is what the Gemara means when it says that "for us [in Bavel], the old moon is covered for 6 hours and the new moon is covered for 18 hours."

In contrast, in Eretz Yisrael -- since the Molad occurred immediately before noon -- the new moon will be visible just before sunset, 6 hours later (and it will remain visible until it sets a few minutes after the sun sets).

However, the old moon was not visible in the morning, since it was within 6 hours of (before) the Molad. The old moon will be visible only before sunset the evening before the Molad, when it is approximately 18 hours (9 degrees) away from the Molad. (The old moon will set before the sun, approximately 36 minutes before the sun sets.) This is what the Gemara means when it says that "for them [in Eretz Yisrael], the old moon is covered for 18 hours and the new moon is covered for 6 hours."

Tzvi Goldman asks further:

Thank you - your explanation was very clear. I am asking about the underlying astronomy - is it really possible to see (a) a waxing crescent moon, only 18 hours after the molad, shortly after sunrise, or (b) a waning crescent moon, only 18 hours before the molad, shortly before sunset?

The Kollel replies:

I suppose you mean to ask the same about the other statements of Rashi - is it really possible to see a waning crescent moon, only 6 hours before the molad, shortly before sunrise, or (b) a waxing crescent moon, only 6 hours after the molad, shortly after sunset?

Truth to be told, the Rambam did not accept this as fact. He writes (in Hilchos Kidush ha'Chodesh 1:3) that the new or old moons cannot be viewed less than approximately 24 hours from the time of the Molad. In Perek 17:3 he writes that less than 18 hours (9 degrees) away from the sun, it is physically impossible for witnesses to see the new moon and those who claim to have seen the moon in such a manner may safely be declared false witnesses.

Dr. Nissim Vidal (formerly of the Royal Observatory at Greenwich) discusses this point at length in his "Kuntrus 24 Sha'ot". He cites the Maharal (Be'er ha'Golah ch. 6) who discusses this point in detail and concludes that Moshe received a prophetic vision that the physical limit for sighting the moon under any condition is 6 hours away from the sun.

Dr. Vidal points out that the current world record (~2007) was 14 hours by the unaided eye and 12 hours with a telescope - but it is constantly changing. We cannot put a physical lower limit on the sighting, only an upper limit. In order to disqualify witnesses, we need a physical lower limit - and for that we must rely on the prophetic limit that we received from Moshe mi'Sinai.

Interestingly, Dr. Vidal brings citations (found in Emunas Chachamim, by Rav Avi'ad Sar Shalom Bazilia) from Johannes Kepler and the Roman astronomer Pliny to the effect that the old moon and the new moon can indeed be sighted on the same day - morning and evening (i.e. less that 7-8 hours from the Molad on either side)! Emunas Chachamim adds that he advised with two of the greatest astronomers of his generation, in Bologna, Italy, as to whether this phenomemon was true of the latitude of Jerusalem as well, and they agreed that it was.

May Hash-m return to us the Beis ha'Mikdash and Sanhedrin, that we may be Mekadesh the moon through sighting once again!

Best regards,

Mordecai Kornfeld

Kollel Iyun Hadaf