[Avodah] zman hadloko erev Shabbos and motzoei Shabbos

[Micha Berger]

On Wed, January 24, 2007 7:44 am, R Zev Sero wrote:
: 24.  The rotation is constant enough, but noon/midnight moves, so the
: length of the day (measured noon-to-noon, or midnight-to-midnight) is
: usually a bit shorter or longer than 24 hours.  And is the same all over
: the planet.

To elaborate....

Ever see on a globe, usually somewhere in the Atlantic, a figure 8 with dates
and numbers on it? That graph shows the shift of noon during the course of the
year. It's called the analemma.

I recommend checking out the web site http://www.analemma.com which explains
the equation of time and its causes quite well, with lots of graphics and
animations.

This effect is also why the earliest Shabbosos in Y-m this year in were Dec 1
and 8th, not the ones straddling the shortest day of the year, Dec 21st.
Because even though the later Fridays were shorter, the days as a whole were
later so that they ended later anyway.

In NYC, the shortest Shabbasos were the 8th and 15th in NYC. Even though the
shift of the whole day in Y-m and NY is the same, since the day shrinks at a
different rate, the crossover points were on different dates.

Tir'u baTov!
-mi

-- 
Micha Berger             Spirituality is like a bird: if you tighten
micha at aishdas.org        your grip on it, it chokes; slacken your grip,
http://www.aishdas.org   and it flies away.
Fax: (270) 514-1507                            - Rav Yisrael Salanter