Re: sunrise and sunset times

[Michael Heerdegen <michael_heerdegen@web.de>]

Conor Matthew <conormatthew@openmailbox.org> writes:

> https://www.gnu.org/software/emacs/manual/html_node/emacs/Sunrise_002fSunset.html
>
> For 0N 0W
>
> Emacs gives
> sunrise 0704
> sunset 1909
>
> http://aa.usno.navy.mil/cgi-bin/aa_rstablew.pl?ID=AA&year=2016&task=0&place=&lon_sign=-1&lon_deg=&lon_min=&lat_sign=1&lat_deg=&lat_min=&tz=1&tz_sign=1
> gives
> sunrise 0703
> sunset 1910

I had a quick look at the Emacs code.  A difference of one minute isn't
surprising: AFAIK the Emacs calculation is exact - it respects all
astronomical effects I know of.  But it doesn't try hard to round to
whole minutes correctly, so the result may differ from the actual event
by an epsilon, where epsilon < 1 min I think.  Maybe epsilon < 30 sec
for aa.usno.navy.mil if they round "correctly", dunno, I don't know that
site.


Michael.