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Re: Wrong times for sunrise/sunset?

From: Óscar Fuentes
Subject: Re: Wrong times for sunrise/sunset?
Date: Sun, 20 Jan 2019 16:00:32 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1.90 (gnu/linux)

Gmane ate my reply, so reposting by e-mail...

Marcin Borkowski <address@hidden> writes:

> C-u M-x sunrise-sunset (and today's date) says:
> Sat, Jan 19, 2019: Sunrise 7:54am (CET), sunset 4:13pm (CET) at Poznań,
> Poland (8:19 hrs daylight)
> Here are my settings:
> (setq calendar-latitude 52.4)
> (setq calendar-longitude 16.917)
> (setq calendar-location-name "Poznań, Poland")
> (BTW, if anyone is ever near here, please drop me a line - we might be
> able to meet in person;-)).
> And C-u M-: calendar-time-zone says (correctly) 60.
> However, (for today)
> says:
> Sunrise Today: 07:51↑ 124° Southeast
> Sunset Today: 16:14↑ 237° Southwest
> I also noticed that other online services give yet other results.
> Anybody knows why the difference(s)?

One possible reason is refraction. A cursory look at solar.el gives the
impression that refraction is not considered, but the astronomy website
you referenced does. This can cause a difference of several minutes.

Another possible reason is not using the same geographical point. 20
kilometers to the west or east can result in minutes of difference.

However, the difference you observe in sunrise (3 minutes) is quite
larger than the diference in sunset (1 minute). At this time of year,
this can mean that your position and the position used by the website
differ on the N/S axis.

Just guessing.

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