[Avodah] zman hadloko erev Shabbos and motzoei Shabbos

[Zev Sero]

Marty Bluke wrote:
> R' Zev Sero wrote:
> <They might have thought that perhaps all of those stars were "kochavim 
> gedolim", and not the three "kochavim beinunim" that are required.
> 
> That is hard to imagine. For example, 50 minutes after shkia it is pitch 
> black outside and you can see countless stars.

Nevertheless, they are bigger than the stars that only become visible
at RT's time, and those are bigger than the ones that aren't visible
even then.  Therefore, the fact that there are so many of them doesn't
absolutely *prove* RT's shita wrong.


> <The truth is that something approximating "Laila DeRT" does match a 
> real phenomenon -- when the sun is 18 degrees below the horizon none of 
> its light is still in the sky, and it's as dark as it's going to get. 
> This is what the charts call "astronomical twilight".
> 
> However, this does not correspond to 72 minutes.

It does, at the equator.  And I doubt that 18 degrees is an exact
shiur, derived from painstaking experimentation that determined that
18 is darker than 17.5, but 18.5 is no darker than 18.  The fact
that 18 is a nice multiple of 6, and that 6 and 12 degrees are also
used as meaningful stages in the fall of night, is unlikely to be a
coincidence.  In other words, 18 is an approximation: at 6 degrees
it's dark enough for ordinary people to call it "night" (which nicely
shtims with shitas hageonim), at 12 degrees it's dark enough to see
the stars generally used for navigation, and at 18 it's about as dark
as it's going to get, and it's time to break out the telescopes and
do some serious stargazing.  Which means that there's no reason
Chazal's shiur has to come to exactly 18 degrees, any more than the
shiur 3/4 mill must be exactly 6 degrees (though in fact it comes
very close).

 
> In NY it varies from approximately 90 - 120 minutes

Chazal didn't give the shiur in NY

> In Yerushalayim it varies from approximately 80 -100 minutes.

See above, but perhaps this shows that, at least according to those
who gave this shiur, a mill is a bit longer than 18 minutes.


> In cities such as Vilna, Moscow, Kovna, etc. in the summer there is no 
> astronomical twilight.

Indeed.  Uvechein?  In those places there is lechol hadeos no alos
hashar in the summer, and therefore the latest time for sefiras haomer
is midnight.  And there are places in the world where even the 3/4 mill
shiur of tzeis hakochavim doesn't exist in the summer -- indeed there
are places where even shkias hachama doesn't happen.  This doesn't
invalidate those shiurim.  So the existence of places and dates where
RT's shiur is never reached doesn't disprove it.  In those places,
midnight will be considered a virtual tzeis hakochavim.


> In any case what we see from here is to say that R"T is a fixed 72 
> minutes is very very difficult.

Oh, that's not difficult, it's impossible.

-- 
Zev Sero               Something has gone seriously awry with this Court's
zev at sero.name          interpretation of the Constitution.
                       	                          - Clarence Thomas