calender/solar.el wrong sunset/sunrise report for polar regions

[Lee Sau Dan]

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Please write in English, because the Emacs maintainers do not have
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In GNU Emacs 20.7.1 (i386-redhat-linux-gnu, X toolkit)
 of Fri Mar 16 2001 on porky.devel.redhat.com
configured using `configure  --mandir=/usr/share/man --infodir=/usr/share/info 
--prefix=/usr --libexecdir=/usr/lib --sharedstatedir=/var --with-gcc --with-pop 
--with-x-toolkit i386-redhat-linux-gnu'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

In calendar-mode,  key "S" triggers  function calendar-sunrise-sunset,
which reports the sunrise/sunset times according to the longtitude and
latitude settings  in some ELisp variables.   When I set  these to the
north-polar region, such as 10E, 80N, it say:

Nov 5, 2001: No sunrise, no sunset at 80N, 10E (24:00 hours daylight)

But this  is wrong.   November is winter  in the  northern hemisphere.
The parts of  the Artic region should have  00:00 hours daylight, i.e.
24:00 night.  A  corresponding error is observed when  the latitude is
set to the Antarctic region, such as 80S.

Sep 23, 2001: No sunrise, no sunset at 90S, 10W (0:00 hours daylight)

The longtitude setting seems to have no effects on this bug.


The following patch to the .el file would correct the problem.  I know
nothing in caldenars and astrology.   Could the author or someone else
verify it?


--- /usr/share/emacs/20.7/lisp/calendar/solar.el        Tue Dec 16 20:12:36 1997
+++ ./solar.el  Mon Nov  5 13:00:39 2001
@@ -316,8 +316,8 @@
     (if (not (and rise-time set-time))
         (if (or (and (> latitude 0) solar-spring-or-summer-season)
                 (and (< latitude 0) (not solar-spring-or-summer-season)))
-          (setq day-length 24)
-          (setq day-length 0))
+          (setq day-length 0)
+          (setq day-length 24))
         (setq day-length (- set-time rise-time)))
     (list (if rise-time (+ rise-time (/ calendar-time-zone 60.0)) nil)
           (if set-time (+ set-time (/ calendar-time-zone 60.0)) nil)



This bug is also observed with Emacs 2.1:

In GNU Emacs 21.1.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2001-10-23 on camaro
configured using `configure  --prefix=/tmp/e21'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Since the source file  solar.el remains basically unchanged from Emacs
20.7 to Emacs 21.1, the above patch is also applicable to the solar.el
code in Emacs 21.1.



Lee Sau Dan
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| e-mail: danlee@informatik.uni-freiburg.de    http://www.csis.hku.hk/~sdlee |
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