Calendar > Moon

["B. T. Raven" <nihil@nihilo.net>]

i)
It's obvious that sunrise-sunset times are dependent on the observer's 
longitude and (to a smaller degree) latitude but is the same true (to any 
degree)of the times of phases of the moon? There is a two minute discrepancy 
between the times reported by the Naval Observatory and by emacs 21.3
Can this be explained by lat. - long. differences among the observers? I 
understood that phases should be dependent only on the relative positions of 
the centers of the sun, earth, and moon. My settings are:

  (setq calendar-latitude 45)
  (setq calendar-longitude -93)

ii) Astronomy question

In the context of describing a storm and catastrophic flooding of the North 
Sea coast, an English medieval chronicler says that Dec. 26, 1287 (Julian, 
or 1-2-1288 Gregorian) is the ninth (day of the) (i.e. two days +/- after 
first quarter). Emacs says it's the 13th (almost full). I was under the 
impression that celestial positions could be extrapolated many millenia 
backwards with great accuracy. Without instruments it's hard to precisely 
determine new and full moon but easy to tell the difference between quarter 
and full. Does any of you have any ideas to explain this discrepancy?

Ed