[Avodah] Molad Alert: Friday night

[Micha Berger]

On Fri, Mar 04, 2011 at 11:08:20AM -0500, Zev Sero wrote:
> On 4/03/2011 10:52 AM, Micha Berger wrote:
>> the month is getting shorter at a rate of something
>> like 3 sec each century.
>
> 3 seconds per century?!  That can't be right.  Right now the received
> value is only 1/3 of a second too long.  You can't tell me that 1500
> years ago the received value was 45 seconds too short, and nobody noticed!

You forget that it requires averaging over many months, as the range is
-12 hr to +16 hr. (Which means there is a skew, since the mean isn't in
the middle of the range.) So, while I was wrong, it's not for this reason.



I posted a formula that gives a 2nd order approximation for current
months:
>     S = 29.5305888531 + 0.00000021621 * T - 3.64E-10 * T^2
> where all time is given in days, and T is days since 1/1/2000. 

Another problem is defining the units of measure in the molad. Because
days are also changing in length, 2ms/century. And the molad requires
relative position of the sun. Not the moon returning to the same spot.
In the above, it's measuring orbits, not lunations. So, ignore it.


So, the phenomenon I'm talking about is real, but I have the numbers off.
Instead of trying to get it right, let me just point you to
http://daattorah.blogspot.com/2008/11/molad-moons-race-against-earth.html
by R Avraham Broide.

The current error is only 0.6 per month -- not 45 sec, but that
accumulated to 2 hrs so far.

:-)BBii!
-Micha

-- 
Micha Berger             Like a bird, man can reach undreamed-of
micha at aishdas.org        heights as long as he works his wings.
http://www.aishdas.org   But if he relaxes them for but one minute,
Fax: (270) 514-1507      he plummets downward.   - Rav Yisrael Salanter