[Avodah] zman hadloko erev Shabbos and motzoei Shabbos

[David E Cohen]

R' Zev Sero wrote:
> The fluctuation of noon/midnight (AKA the Equation of Time) does not
> depend on the season but on the position of the earth in its elliptical
> orbit, and is therefore the same everywhere.  

I believe that it's actually both.  The "Equation of Time" is really the sum
of two separate factors (though RZS is correct in saying that it is the same
everywhere).

One, as RZS mentioned, is the position of the Earth in its elliptical orbit,
which results in different speeds of rotation around the sun.  When the
Earth is closer to the sun, and thus moving faster in its orbit, the sun has
"more catching up to do" each day.

The other factor is, in fact, the tilt of the Earth, which results in all of
the sun's motion being along the "east-west axis" (the "celestial equator")
at the equinoxes, but less of it being along that axis at other times.
Thus, it takes longer at the solstices than at the equinoxes for the sun to
"catch up" with the change in the Earth's position in its orbit that
happened over the past day.

I second R' Micha's recommendation of http://www.analemma.com, which
explains this much better than I can.

To bring this back to Avodah territory, in Iggeros Moshe OC 24, where R'
Moshe Feinstein is explaining how he made the luach of his yeshiva, he
writes that there are times of year when the morning is longer, and there
are times of year when the afternoon is longer.  I have seen this explained
(in R' Blumenkrantz's Pesach book, IIRC) as meaning that R' Moshe held that
the mean solar noon should be considered chatzos all year round, and all
morning zemanim should be calculated using the time from sunrise until then,
and all afternoon zemanim should be calculated using the time from then
until sunset, even though there are times when the "morning" could be 20
minutes longer than the "afternoon," and vice versa.

I have a difficult time understanding this.  First of all, R' Moshe writes
that chatzos is "ke-she-ba hashemesh be-emtza` ha-darom shaveh la-`olam."
The time when the sun is directly to the south (here in the Northern
Temperate Zone) is the actual solar noon, not the mean solar noon.
Furthermore, I believe that the everyday use of the mean solar noon is a
relatively recent phenomenon (a few hundred years old).  It predates the
adoption of standard time zones, of course, but it postdates the adoption of
the clock that has 24 equal hours.  For a time, people were using these
clocks, but resetting them to 12:00 every day at the actual solar noon.
Zeminim be-Halakhah, by R' Chaim Benish, has some pictures of charts from
early-20th-century Jerusalem that list zemanim in 3 forms (besides the
"sha`on Eretz Yisra'el," which was reset every day at sunset, a different
matter altogether): actual solar time, mean solar time, and standard time).

My point is that mean solar noon seems simple to us, since it's at the same
time on our clocks every day.  We are more in touch with our clocks than
with the sun, so we pull out our calculators and computer programs to plug
in the Equation of Time and figure out when the actual solar noon is.  But
when the noon on people's clocks (and before that, sundials) was actual
solar noon, they would have had to know the Equation of Time in order to
calculate mean solar noon.  I find it difficult to believe that this is what
Chazal had in mind.

If I were reading R' Moshe's words on my own, I would think that he was
simply referring to the fact that chatzos will not be exactly halfway
between sunrise and sunset, since the sun's declination and the Equation of
Time do change slightly within the course of a day.  On the other hand,
though, the total effect of this would probably not be more than one or two
minutes, which is not nearly as substantial as what R' Blumenkrantz is
describing.

Can somebody who has an MTJ luach report as to which explanation of R'
Moshe's shitah is correct?  If R' Blumenkrantz's understanding is correct,
what was R' Moshe's sevara?

--D.C.