sunrise and sunset times

[Conor Matthew]

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

and http://www.risacher.org/sunwait/
sunwait list angle 0 0N 0W
gives
sunrise 0706
sunset 1906

for today 29th.

Does http://aa.usno.navy.mil/data/docs/RS_OneYear.php give the correct
answer?

Best wishes,

Conor

[Michael Heerdegen]

Conor Matthew <conorm...@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.

[Pierpaolo Bernardi]

On Fri, Jul 29, 2016 at 4:34 PM, Conor Matthew
<conorm...@openmailbox.org> wrote:
> https://www.gnu.org/software/emacs/manual/html_node/emacs/Sunrise_002fSunset.html
>
> For 0N 0W

The apparent position of the sun depends in addition to the actual
position, also on some atmospheric parameters (air temperature and
pression) which usually are only guessed.

So, small differences due to slightly different guesses for these
parameters are to be expected.