Dan,
Using only your April data, and assuming:
1. day length is the difference of the sunset and sunrise (as opposed to
the daylength stated),
2. sunrise and sunset are when the center of the sun is on the horizon
3. my modern source of solar declination data is "good enough"
4. your table of values is for the Julian calendar, which for the year
in question is offset from the Gregorian calendar by 11 days,
then, by varying latitude to minimize the Sum of Squares of the
differences between true day lengths and the representative day length
stated .... I get a latitude of 44.413N, which would correspond to
Bucarest.
If I could use your table of data for the full year, the result would of
course be different - better, I would hope, but possibly not!
As yet, I have no idea why the stated day length is not the same as the
difference of the sunrise and sunset.
Steve
On 2019-08-09 1:06 a.m., Dan-George Uza wrote:
Hello all,
I have seen an old calendar from 1793 which lists for every month
sunrise and sunset times as well as day and night duration. For
example, taking the month of April: sunrise at 5 h 20 m, sunset at 7 h
14 m; day length 13 h 20 min, night length 10 h 40 m.
Somebody asked me if it would be possible to establish the approximate
geographical area for these predictions.
I'm pretty sure it's not possible. Back then they used true solar time
(or perhaps mean solar time?) so I guess these hours would have been
valid for a whole parallel of latitude, with variations once you go
north or south.
Nevertheless, I made a simulation and realized that I cannot get close
to these numbers. I don't know why. Perhaps because back then sunrise
and sunset was not counted by solar limb, but by geometric center of
the Sun? How did they do it?
Regards,
--
Dan-George Uza
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