Subject: bug#61460: 30.0.50; Calendar shows eclipse for quarter moon

From: Michael Heerdegen <[email-masked]>
Date: Mon, 13 Feb 2023 05:52:22 +0100

Michael Heerdegen <[email-masked]> writes:

> >           (phase-name (cond ((= phase 0) "Solar")
> >                             ((= phase 2) "Lunar")
> >                             (t ""))))
> > -    (cond ((< moon-lat 2.42600766e-1)
> > +    (cond ((string= phase-name "")
> > +	   "")
> > +	  ((< moon-lat 2.42600766e-1)
> >  	   (concat "** " phase-name " Eclipse **"))
> >  	  ((< moon-lat 0.37)
> >  	   (concat "** " phase-name " Eclipse possible **"))
>

> (1) AFAIU, the "phase name" is derived from one of four values of the
> moon "phase".  Is this really good enough to decide whether it is new
> moon or full moon?

I understand this now: That code is only ever called at the day of the
start of each (quarter) moon phase, so your patch should be correct, in
my opinion.

> (2) https://en.wikipedia.org/wiki/Lunar_node tells that the limit for
> the longitude of the moon is different for lunar vs. solar eclipses.
> The same will be the case when we test the latitude.  The test we
> currently use doesn't reflect that.  Should it?

I still have that question, though.  I only found values for the
longitude, we test the latitude (which is available in the surrounding
code, this should be no problem).  But it really looks to me like those
two values 0.24 and 0.37 should depend on the moon phase (or kind of
eclipse respectively) instead of testing both.

Michael.