Re: Calendar > Moon

[Bauke Jan Douma <bjdouma@xs4all.nl>]

B. T. Raven wrote on 19-05-07 14:26:
> 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?

i.  yes it could be explained by diff. in lat./long. I don't know
     which position either of them uses to calculate the times, nor
     the algorithms used.

ii. how is Dec. 26, 1287 as you say 1-2-1288 Gregorian?  If it's anything,
     it's 6 jan. 1288 'gregorian' (+11 days).

bjd