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Re: Wrong times for sunrise/sunset?


From: Marcin Borkowski
Subject: Re: Wrong times for sunrise/sunset?
Date: Sun, 20 Jan 2019 07:10:37 +0100
User-agent: mu4e 1.1.0; emacs 27.0.50

On 2019-01-20, at 06:52, ken <address@hidden> wrote:

> On 1/19/19 10:25 AM, Marcin Borkowski wrote:
>> Hello,
>>
>> C-u M-x sunrise-sunset (and today's date) says:
>>
>> --8<---------------cut here---------------start------------->8---
>> Sat, Jan 19, 2019: Sunrise 7:54am (CET), sunset 4:13pm (CET) at Poznań,
>> Poland (8:19 hrs daylight)
>> --8<---------------cut here---------------end--------------->8---
>>
>> Here are my settings:
>>
>> --8<---------------cut here---------------start------------->8---
>> (setq calendar-latitude 52.4)
>> (setq calendar-longitude 16.917)
>> (setq calendar-location-name "Poznań, Poland")
>> --8<---------------cut here---------------end--------------->8---
>>
>> (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, https://www.timeanddate.com/astronomy/poland/poznan (for today)
>> says:
>>
>> --8<---------------cut here---------------start------------->8---
>> Sunrise Today: 07:51↑ 124° Southeast
>> Sunset Today: 16:14↑ 237° Southwest
>> --8<---------------cut here---------------end--------------->8---
>>
>> I also noticed that other online services give yet other results.
>>
>> Anybody knows why the difference(s)?
>>
>> TIA,
>>
>> --
>> Marcin Borkowski
>> http://mbork.pl
>
> Reading on sunrise-sunset a long time ago, I was given to understand
> that, while the calculations are unambiguous, the perception of those
> times is open to interpretation. Especially when the sun (and other
> astronomical objects) is low to the horizon, the Earth's atmosphere acts
> as a lens, enabling us to see the sun (etc.) even before and after it is
> in our straight line-of-sight. That is, the atmosphere's lensing effect
> allows us to see a little bit over the horizon. The calculations
> performed by emacs do not compensate for the atmospheric magic. But
> other sources, rather than being accused of inaccuracy by the public who
> might look out the window, typically amend the purely physical reckoning
> to accommodate earthly perceptions.

Thanks, that would explain a lot.

Best,

-- 
Marcin Borkowski
http://mbork.pl



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