[Avodah] Where is the Molad announced for?

[Micha Berger]

Branching new thread from: Vizhnitz Rebbe Asks Chasidim To Make Kiddush
This Shabbos

On Mon, Dec 21, 2020 at 10:01:15AM -0500, Prof. Levine wrote:
> BTW, in most shuls the Molad is announced using Jerusalem solar time,
> not local time where one is or even local Jerusalem time.

Because the practice is older than railroads and timezones.

Except it isn't solar time for Yerushalayim. If you figure out the mean
time of lunation, it's accurate for a meridian somewhere even further
East than the Jews in Bavel. Qandahar Afghanistan or so.

And if you add time after that, because there has to be some sliver
of the new moon for eidim to see, you get even further east.

However, the average time between new moons (lunation) is not a constant
down the centuries. It is getting longer; in other words, the moon is
slowing down. Energy is being spent pulling the tides around. And that
drag is making the moon's trip around the earth take longer.

(Also, the earth is spinning slower for the same reason. In other words,
our units of measure -- days, hours (day / 24) and chalaqim are longer
than Chazal's. But that's a smaller effect.)

So, nowadays the mean time between lunations (even when measured in days
and pieces of days) is just a shade longer than the molad. And this has
been adding up to the molad time every month for centuries so that we're
now talking the ballpark of a couple of hours.

I would therefore think that better than asking where the molad is most
accurate *now*, but for what meridian was the molad accurate for when
the din was established?

As I've posted in the past, we can equally ask: When the molad *interval*
was most accurate, on whose clock was the *time* the molad actually
happened similarly most accurate? Those are likely the same question
because the molad interval was most accurate in the mid-4th cent. Around
when our calendar was set up -- our most likely generation for enacting
the announcement of the molad time.

So, to ask the updated question: Where was the molad most accurate in the
last days of the amora'im? The answer still isn't Yerushalayim ih"q. But
someplace where the clock would read 23 min or so later. In today's
terms, it's somewhere around where Saudi Arabia, Iraq and Jordan meet.

Let's say this line of reasoning is correct. (I am pretty sure the
actual math is; Google showed me others who reached the same conclusion.)
Why would they have chosen the clock at that meridian?

One explanation I find plausible: It's somewhere around the middle of
the Yishuv in those days, around half-way between EY and Bavel. So,
if you announce the time for the middle of the region, you minimize how
far off it is in everyone's local time.

I like to call it "Ur Kasdim Time".

Tir'u baTov!
-Micha

-- 
Micha Berger                     Time flies...
http://www.aishdas.org/asp               ... but you're the pilot.
Author: Widen Your Tent                          - R' Zelig Pliskin
- https://amzn.to/2JRxnDF