Hi, In old calendars and almanacs sunrise and sunset times were always computed for the solar center and also neglected refraction corrections, so assume a zenith distance of exactly 90 degrees.
Is the sunset time you cited for April correct? I would actually expect it to be 6 h 40 m, the time which you cite is perhaps for the end of (astronomical) twilight. Rob van Gent From: sundial <[email protected]> On Behalf Of Dan-George Uza Sent: Fri 09 August 2019 10:07 To: Sundial List <[email protected]> Subject: Sunrise/sunset in old calendars/almanacs 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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