Talk:Molad

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Various problems

My comments in red:

The molad emtzai (average molad, used for the traditional Hebrew calendar) is based on a constant interval cycle that is widely but incorrectly regarded as an approximation of the time in Jerusalem of the mean lunar conjunction.—This has two problems. One is that the mean lunar conjunction (as opposed to the time between specific conjunctions) does not depend on a position on earth but is the same for all positions. (The main thing that differs between locations is the time of day when the conjunction occurs. Two locations do observe the conjunction at slightly different moments, but on average that difference is a constant so it cancels out when subtracting conjunctions.) Another problem is that it really was intended to be an accurate long-term average as in fact it was and is.— Each molad moment occurs exactly 29 days 12 hours 44 minutes and 3+1/3 seconds after the previous molad moment. This interval is numerically exactly the same as the length of the mean synodic month that was published by Ptolemy in the Almagest, who cited Hipparchus as its source.—Yes, and known even earlier in Babylonia.— Although in the era of Hipparchus (2nd century BC) this interval was equal —This statement is more or less correct, but its significance is unclear as nobody in those days could measure to the precision required to notice the difference.— to the average time between lunar conjunctions, mean lunation intervals get progressively shorter due to tidal transfer of angular momentum from Earth to Moon —The linked-to page does not seem to mention angular momentum at all and anyway we should try to be accessible to a general audience. A more understandable description is that the revolution of the moon around the earth is slowing down but the rotation of the earth is slowing down even more, so the length of the month is getting shorter when measured in days—, so that in the present era the molad interval is about 3/5 of a second too long.

Historically, the original molad reference meridian of longitude—I wonder if a solid reference can be given that there was such a thing as an original "reference meridian". I didn't see any mention of such a concept in the books and articles I have read about the origin of the calendar. I think this is just a modern calculation of the meridian where the calculated and actual molads best coincided, but there is no evidence that this was understood at the time.— was halfway between the Nile river and the end of the Euphrates river, but the excess length of the molad interval causes it to drift progressively eastward at an accelerating rate — in the present era it is at a meridian that passes near Qandahar, Afghanistan!—I propose deleting this paragraph, no reader will make any sense of it.

McKay (talk) 06:27, 5 September 2011 (UTC)[reply]

Molad Reference Meridian

As mentioned above, this whole section is unsourced and appears to be based on original research. I support the proposal to delete this section unless a reliable verifiable source can be found. AstroLynx (talk) 15:28, 2 September 2019 (UTC)[reply]

As one who has actually calculated many Jewish dates, no reference meridian is needed, and it does not appear in any calculation. You can assume any meridian you want, and all Jewish dates are still correct. — Joe Kress (talk) 15:55, 2 September 2019 (UTC)[reply]

Agreed, so what is your suggestion for the whole final paragraph "Although it is widely assumed ... provided that the start of each date is taken as local mean sunset."? Delete or keep?

In the same section I would also suggest to remove every mention of a Reference Meridian and substitute "Adam, the first man," and "God" for "Adam haRishon" and "haShem". AstroLynx (talk) 16:22, 2 September 2019 (UTC)[reply]

I agree. Remove all mention of a reference meridian. Change those Hebrew words to English because this is an English language article. — Joe Kress (talk) 00:31, 4 September 2019 (UTC)[reply]

Joe Kress, The source for a specific meridian is here. yoisef yitzchok-talk, 10 Elul 5779. 19:07, 9 September 2019 (UTC)[reply]

It would be much more useful if you could refer to a translation (preferably in English) of this text. Now we have to take your word that the text actually says what you claim it says. AstroLynx (talk) 07:47, 10 September 2019 (UTC)[reply]

It's 'Sefer ha-'ibbur' of Abraham ibn ezra. I don't know where there is a translation of this book. yoisef yitzchok-talk, 10 Elul 5779. 09:14, 10 September 2019 (UTC)[reply]

A commentary that a specific meridian is important for the calendar, contrary to the great majority of descriptions, is no more than an obscure commentary unless it can be shown that this view is widespread. McKay (talk) 07:20, 13 September 2019 (UTC)[reply]

I added a source. It seems reliable to me, however there may be some misunderstandings in this paragraph as it seems that the conclusion in the article is that the original meridian was not exactly in between Jerusalem an Babylonia. This may need further editing.185.182.71.11 (talk) 12:02, 31 January 2022 (UTC)[reply]