GNU bug report logs - #61460
30.0.50; Calendar shows eclipse for quarter moon

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From: Ulrich Mueller <ulm <at> gentoo.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Michael Heerdegen <michael_heerdegen <at> web.de>, 61460 <at> debbugs.gnu.org
Subject: bug#61460: 30.0.50; Calendar shows eclipse for quarter moon
Date: Mon, 13 Feb 2023 14:30:59 +0100

>> Thank you very much.  So "argument" is like the argument of a complex
>> number, and this one correlates with the latitude, or something like
>> that.

I wondered about the term too, but it appears to be very old. It can
be found with its modern definition already in "The Equatorie of the
Planetis" from 1393 [1]: "Þe argument of latitude is þe distaunce of
þe mone from þe hed of his dragoun þat is in þe ecliptik lyne."
(The "head of the dragon" is the ascending node.)

[1] https://www.google.de/books/edition/The_Authorship_of_the_Equatorie_of_the_P/eG3JBxlp0LEC?hl=de&gbpv=1&dq=%22argument%20of%20latitude%22&pg=PA235&printsec=frontcover

>> Hmm, I think adding some small comments to the code would not harm,
>> you seem to understand it.

> Yes, please add such comments there, and thanks.

This would require that I understand the code. :) I happen to have a
copy of Dershowitz & Reingold "Calendrical Calculations" (3rd ed.).
The calculations of the lunar orbit there (on pages 193-207) are well
commented, but seem to be very different from those in lunar.el
(for example, they contain corrections for the gravitational pull of
Venus and Jupiter).

So, I'll see what I can do, but please don't expect anything soon.

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