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1 ;;; solar.el --- calendar functions for solar events.
2
3 ;; Copyright (C) 1992, 1993 Free Software Foundation, Inc.
4
5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
6 ;; Keywords: calendar
7 ;; Human-Keywords: sunrise, sunset, equinox, solstice, calendar, diary,
8 ;; holidays
9
10 ;; This file is part of XEmacs.
11
12 ;; XEmacs is free software; you can redistribute it and/or modify it
13 ;; under the terms of the GNU General Public License as published by
14 ;; the Free Software Foundation; either version 2, or (at your option)
15 ;; any later version.
16
17 ;; XEmacs is distributed in the hope that it will be useful, but
18 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20 ;; General Public License for more details.
21
22 ;; You should have received a copy of the GNU General Public License
23 ;; along with XEmacs; see the file COPYING. If not, write to the Free
24 ;; Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
25
26 ;;; Commentary:
27
28 ;; This collection of functions implements the features of calendar.el,
29 ;; diary.el, and holiday.el that deal with times of day, sunrise/sunset, and
30 ;; eqinoxes/solstices.
31
32 ;; Based on the ``Almanac for Computers 1984,'' prepared by the Nautical
33 ;; Almanac Office, United States Naval Observatory, Washington, 1984 and
34 ;; on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
35 ;; Willmann-Bell, Inc., 1985.
36 ;;
37 ;; WARNINGS:
38 ;; 1. SUNRISE/SUNSET calculations will be accurate only to +/- 2 minutes.
39 ;; Locations should be between +/- 65 degrees of latitude.
40 ;; Dates should be in the latter half of the 20th century.
41 ;;
42 ;; 2. Equinox/solstice times will be accurate only to +/- 15 minutes.
43
44 ;; The author would be delighted to have an astronomically more sophisticated
45 ;; person rewrite the code for the solar calculations in this file!
46
47 ;; Comments, corrections, and improvements should be sent to
48 ;; Edward M. Reingold Department of Computer Science
49 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
50 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
51 ;; Urbana, Illinois 61801
52
53 ;;; Code:
54
55 (if (fboundp 'atan)
56 (require 'lisp-float-type)
57 (error "Solar/lunar calculations impossible since floating point is unavailable."))
58
59 (require 'cal-dst)
60
61 ;;;###autoload
62 (defvar calendar-time-display-form
63 '(12-hours ":" minutes am-pm
64 (if time-zone " (") time-zone (if time-zone ")"))
65 "*The pseudo-pattern that governs the way a time of day is formatted.
66
67 A pseudo-pattern is a list of expressions that can involve the keywords
68 `12-hours', `24-hours', and `minutes', all numbers in string form,
69 and `am-pm' and `time-zone', both alphabetic strings.
70
71 For example, the form
72
73 '(24-hours \":\" minutes
74 (if time-zone \" (\") time-zone (if time-zone \")\"))
75
76 would give military-style times like `21:07 (UTC)'.")
77
78 ;;;###autoload
79 (defvar calendar-latitude nil
80 "*Latitude of `calendar-location-name' in degrees.
81
82 The value can be either a decimal fraction (one place of accuracy is
83 sufficient), + north, - south, such as 40.7 for New York City, or the value
84 can be a vector [degrees minutes north/south] such as [40 50 north] for New
85 York City.
86
87 This variable should be set in site-local.el.")
88
89 ;;;###autoload
90 (defvar calendar-longitude nil
91 "*Longitude of `calendar-location-name' in degrees.
92
93 The value can be either a decimal fraction (one place of accuracy is
94 sufficient), + east, - west, such as -73.9 for New York City, or the value
95 can be a vector [degrees minutes east/west] such as [73 55 west] for New
96 York City.
97
98 This variable should be set in site-local.el.")
99
100 (defsubst calendar-latitude ()
101 "Convert calendar-latitude to a signed decimal fraction, if needed."
102 (if (numberp calendar-latitude)
103 calendar-latitude
104 (let ((lat (+ (aref calendar-latitude 0)
105 (/ (aref calendar-latitude 1) 60.0))))
106 (if (equal (aref calendar-latitude 2) 'north)
107 lat
108 (- lat)))))
109
110 (defsubst calendar-longitude ()
111 "Convert calendar-longitude to a signed decimal fraction, if needed."
112 (if (numberp calendar-longitude)
113 calendar-longitude
114 (let ((long (+ (aref calendar-longitude 0)
115 (/ (aref calendar-longitude 1) 60.0))))
116 (if (equal (aref calendar-longitude 2) 'east)
117 long
118 (- long)))))
119
120 ;;;###autoload
121 (defvar calendar-location-name
122 '(let ((float-output-format "%.1f"))
123 (format "%s%s, %s%s"
124 (if (numberp calendar-latitude)
125 (abs calendar-latitude)
126 (+ (aref calendar-latitude 0)
127 (/ (aref calendar-latitude 1) 60.0)))
128 (if (numberp calendar-latitude)
129 (if (> calendar-latitude 0) "N" "S")
130 (if (equal (aref calendar-latitude 2) 'north) "N" "S"))
131 (if (numberp calendar-longitude)
132 (abs calendar-longitude)
133 (+ (aref calendar-longitude 0)
134 (/ (aref calendar-longitude 1) 60.0)))
135 (if (numberp calendar-longitude)
136 (if (> calendar-longitude 0) "E" "W")
137 (if (equal (aref calendar-latitude 2) 'east) "E" "W"))))
138 "*Expression evaluating to name of `calendar-longitude', calendar-latitude'.
139 For example, \"New York City\". Default value is just the latitude, longitude
140 pair.
141
142 This variable should be set in site-local.el.")
143
144 (defvar solar-n-hemi-seasons
145 '("Vernal Equinox" "Summer Solstice" "Autumnal Equinox" "Winter Solstice")
146 "List of season changes for the northern hemisphere.")
147
148 (defvar solar-s-hemi-seasons
149 '("Autumnal Equinox" "Winter Solstice" "Vernal Equinox" "Summer Solstice")
150 "List of season changes for the southern hemisphere.")
151
152 (defun solar-setup ()
153 "Prompt user for latitude, longitude, and time zone."
154 (beep)
155 (if (not calendar-longitude)
156 (setq calendar-longitude
157 (solar-get-number
158 "Enter longitude (decimal fraction; + east, - west): ")))
159 (if (not calendar-latitude)
160 (setq calendar-latitude
161 (solar-get-number
162 "Enter latitude (decimal fraction; + north, - south): ")))
163 (if (not calendar-time-zone)
164 (setq calendar-time-zone
165 (solar-get-number
166 "Enter difference from Coordinated Universal Time (in minutes): "))))
167
168 (defun solar-get-number (prompt)
169 "Return a number from the minibuffer, prompting with PROMPT.
170 Returns nil if nothing was entered."
171 (let ((x (read-string prompt "")))
172 (if (not (string-equal x ""))
173 (string-to-int x))))
174
175 (defsubst solar-sin-degrees (x)
176 (sin (degrees-to-radians x)))
177
178 (defsubst solar-cosine-degrees (x)
179 (cos (degrees-to-radians x)))
180
181 (defun solar-tangent-degrees (x)
182 (tan (degrees-to-radians x)))
183
184 (defun solar-xy-to-quadrant (x y)
185 "Determines the quadrant of the point X, Y."
186 (if (> x 0)
187 (if (> y 0) 1 4)
188 (if (> y 0) 2 3)))
189
190 (defun solar-degrees-to-quadrant (angle)
191 "Determines the quadrant of ANGLE."
192 (1+ (floor (mod angle 360) 90)))
193
194 (defun solar-arctan (x quad)
195 "Arctangent of X in quadrant QUAD."
196 (let ((deg (radians-to-degrees (atan x))))
197 (cond ((equal quad 2) (+ deg 180))
198 ((equal quad 3) (+ deg 180))
199 ((equal quad 4) (+ deg 360))
200 (t deg))))
201
202 (defun solar-arccos (x)
203 (let ((y (sqrt (- 1 (* x x)))))
204 (solar-arctan (/ y x) (solar-xy-to-quadrant x y))))
205
206 (defun solar-arcsin (y)
207 (let ((x (sqrt (- 1 (* y y)))))
208 (solar-arctan (/ y x) (solar-xy-to-quadrant x y))))
209
210 (defconst solar-earth-inclination 23.441884
211 "Inclination of earth's equator to its solar orbit in degrees.")
212
213 (defconst solar-cos-inclination (solar-cosine-degrees solar-earth-inclination)
214 "Cosine of earth's inclination.")
215
216 (defconst solar-sin-inclination (solar-sin-degrees solar-earth-inclination)
217 "Sine of earth's inclination.")
218
219 (defconst solar-earth-orbit-eccentricity 0.016718
220 "Eccentricity of orbit of the earth around the sun.")
221
222 (defsubst solar-degrees-to-hours (deg)
223 (/ deg 15.0))
224
225 (defsubst solar-hours-to-days (hour)
226 (/ hour 24.0))
227
228 (defun solar-longitude-of-sun (day)
229 "Longitude of the sun at DAY in the year."
230 (let ((mean-anomaly (- (* 0.9856 day) 3.289)))
231 (mod (+ mean-anomaly
232 (* 1.916 (solar-sin-degrees mean-anomaly))
233 (* 0.020 (solar-sin-degrees (* 2 mean-anomaly)))
234 282.634)
235 360)))
236
237 (defun solar-right-ascension (longitude)
238 "Right ascension of the sun, given its LONGITUDE."
239 (solar-degrees-to-hours
240 (solar-arctan
241 (* solar-cos-inclination (solar-tangent-degrees longitude))
242 (solar-degrees-to-quadrant longitude))))
243
244 (defun solar-declination (longitude)
245 "Declination of the sun, given its LONGITUDE."
246 (solar-arcsin
247 (* solar-sin-inclination
248 (solar-sin-degrees longitude))))
249
250 (defun solar-sunrise (date)
251 "Calculates the *standard* time of sunrise for Gregorian DATE.
252 Calculation is for location given by `calendar-latitude' and
253 `calendar-longitude'.
254
255 Returns a decimal fraction of hours. Returns nil if the sun does not rise at
256 that location on that day."
257 (let* ((day-of-year (calendar-day-number date))
258 (approx-sunrise
259 (+ day-of-year
260 (solar-hours-to-days
261 (- 6 (solar-degrees-to-hours (calendar-longitude))))))
262 (solar-longitude-of-sun-at-sunrise
263 (solar-longitude-of-sun approx-sunrise))
264 (solar-right-ascension-at-sunrise
265 (solar-right-ascension solar-longitude-of-sun-at-sunrise))
266 (solar-declination-at-sunrise
267 (solar-declination solar-longitude-of-sun-at-sunrise))
268 (cos-local-sunrise
269 (/ (- (solar-cosine-degrees (+ 90 (/ 50.0 60.0)))
270 (* (solar-sin-degrees solar-declination-at-sunrise)
271 (solar-sin-degrees (calendar-latitude))))
272 (* (solar-cosine-degrees solar-declination-at-sunrise)
273 (solar-cosine-degrees (calendar-latitude))))))
274 (if (<= (abs cos-local-sunrise) 1);; otherwise, no sunrise that day
275 (let* ((local-sunrise (solar-degrees-to-hours
276 (- 360 (solar-arccos cos-local-sunrise))))
277 (local-mean-sunrise
278 (mod (- (+ local-sunrise solar-right-ascension-at-sunrise)
279 (+ (* 0.065710 approx-sunrise)
280 6.622))
281 24)))
282 (+ (- local-mean-sunrise (solar-degrees-to-hours (calendar-longitude)))
283 (/ calendar-time-zone 60.0))))))
284
285 (defun solar-sunset (date)
286 "Calculates the *standard* time of sunset for Gregorian DATE.
287 Calculation is for location given by `calendar-latitude' and
288 `calendar-longitude'.
289
290 Returns a decimal fractions of hours. Returns nil if the sun does not set at
291 that location on that day."
292 (let* ((day-of-year (calendar-day-number date))
293 (approx-sunset
294 (+ day-of-year
295 (solar-hours-to-days
296 (- 18 (solar-degrees-to-hours (calendar-longitude))))))
297 (solar-longitude-of-sun-at-sunset
298 (solar-longitude-of-sun approx-sunset))
299 (solar-right-ascension-at-sunset
300 (solar-right-ascension solar-longitude-of-sun-at-sunset))
301 (solar-declination-at-sunset
302 (solar-declination solar-longitude-of-sun-at-sunset))
303 (cos-local-sunset
304 (/ (- (solar-cosine-degrees (+ 90 (/ 50.0 60.0)))
305 (* (solar-sin-degrees solar-declination-at-sunset)
306 (solar-sin-degrees (calendar-latitude))))
307 (* (solar-cosine-degrees solar-declination-at-sunset)
308 (solar-cosine-degrees (calendar-latitude))))))
309 (if (<= (abs cos-local-sunset) 1);; otherwise, no sunset that day
310 (let* ((local-sunset (solar-degrees-to-hours
311 (solar-arccos cos-local-sunset)))
312 (local-mean-sunset
313 (mod (- (+ local-sunset solar-right-ascension-at-sunset)
314 (+ (* 0.065710 approx-sunset) 6.622))
315 24)))
316 (+ (- local-mean-sunset (solar-degrees-to-hours (calendar-longitude)))
317 (/ calendar-time-zone 60.0))))))
318
319 (defun solar-adj-time-for-dst (date time &optional style)
320 "Adjust decimal fraction standard TIME on DATE to account for dst.
321 Returns a list (date adj-time zone) where `date' and `time' are the values
322 adjusted for `zone'; here `date' is a list (month day year), `time' is a
323 decimal fraction time, and `zone' is a string.
324
325 Optional parameter STYLE forces the result time to be standard time when its
326 value is 'standard and daylight savings time (if available) when its value is
327 'daylight.
328
329 Conversion to daylight savings time is done according to
330 `calendar-daylight-savings-starts', `calendar-daylight-savings-ends',
331 `calendar-daylight-savings-starts-time',
332 `calendar-daylight-savings-ends-time', and
333 `calendar-daylight-savings-offset'."
334
335 (let* ((year (extract-calendar-year date))
336 (rounded-abs-date (+ (calendar-absolute-from-gregorian date)
337 (/ (round (* 60 time)) 60.0 24.0)))
338 (dst-starts (and calendar-daylight-savings-starts
339 (+ (calendar-absolute-from-gregorian
340 (eval calendar-daylight-savings-starts))
341 (/ calendar-daylight-savings-starts-time
342 60.0 24.0))))
343 (dst-ends (and calendar-daylight-savings-ends
344 (+ (calendar-absolute-from-gregorian
345 (eval calendar-daylight-savings-ends))
346 (/ (- calendar-daylight-savings-ends-time
347 calendar-daylight-time-offset)
348 60.0 24.0))))
349 (dst (and (not (eq style 'standard))
350 (or (eq style 'daylight)
351 (and dst-starts dst-ends
352 (or (and (< dst-starts dst-ends);; northern hemi.
353 (<= dst-starts rounded-abs-date)
354 (< rounded-abs-date dst-ends))
355 (and (< dst-ends dst-starts);; southern hemi.
356 (or (< rounded-abs-date dst-ends)
357 (<= dst-starts rounded-abs-date)))))
358 (and dst-starts (not dst-ends)
359 (<= dst-starts rounded-abs-date))
360 (and dst-ends (not dst-starts)
361 (< rounded-abs-date dst-ends)))))
362 (time-zone (if dst
363 calendar-daylight-time-zone-name
364 calendar-standard-time-zone-name))
365 (time (+ rounded-abs-date
366 (if dst (/ calendar-daylight-time-offset 24.0 60.0) 0))))
367 (list (calendar-gregorian-from-absolute (truncate time))
368 (* 24.0 (- time (truncate time)))
369 time-zone)))
370
371 (defun solar-time-string (time time-zone)
372 "Printable form for decimal fraction TIME on DATE.
373 Format used is given by `calendar-time-display-form'."
374 (let* ((time (round (* 60 time)))
375 (24-hours (/ time 60))
376 (minutes (format "%02d" (% time 60)))
377 (12-hours (format "%d" (1+ (% (+ 24-hours 11) 12))))
378 (am-pm (if (>= 24-hours 12) "pm" "am"))
379 (24-hours (format "%02d" 24-hours)))
380 (mapconcat 'eval calendar-time-display-form "")))
381
382 (defun solar-sunrise-sunset (date)
383 "String giving local times of sunrise and sunset on Gregorian DATE."
384 (let* ((rise (solar-sunrise date))
385 (adj-rise (if rise (solar-adj-time-for-dst date rise)))
386 (set (solar-sunset date))
387 (adj-set (if set (solar-adj-time-for-dst date set))))
388 (format "%s, %s at %s"
389 (if (and rise (calendar-date-equal date (car adj-rise)))
390 (concat "Sunrise " (apply 'solar-time-string (cdr adj-rise)))
391 "No sunrise")
392 (if (and set (calendar-date-equal date (car adj-set)))
393 (concat "sunset " (apply 'solar-time-string (cdr adj-set)))
394 "no sunset")
395 (eval calendar-location-name))))
396
397 (defun solar-apparent-longitude-of-sun (date)
398 "Apparent longitude of the sun on Gregorian DATE."
399 (let* ((time (/ (- (calendar-absolute-from-gregorian date)
400 (calendar-absolute-from-gregorian '(1 0.5 1900)))
401 36525))
402 (l (+ 279.69668
403 (* 36000.76892 time)
404 (* 0.0003025 time time)))
405 (m (+ 358.47583
406 (* 35999.04975 time)
407 (* -0.000150 time time)
408 (* -0.0000033 time time time)))
409 (c (+ (* (+ 1.919460
410 (* -0.004789 time)
411 (* -0.000014 time time))
412 (solar-sin-degrees m))
413 (* (+ 0.020094
414 (* -0.000100 time))
415 (solar-sin-degrees (* 2 m)))
416 (* 0.000293
417 (solar-sin-degrees (* 3 m)))))
418 (L (+ l c))
419 (omega (+ 259.18
420 (* -1934.142 time)))
421 (app (+ L
422 -0.00569
423 (* -0.00479
424 (solar-sin-degrees omega)))))
425 app))
426
427 (defun solar-ephemeris-correction (year)
428 "Difference in minutes between Ephemeris time and UTC in YEAR.
429 Value is only an approximation."
430 (let ((T (/ (- year 1900) 100.0)))
431 (+ 0.41 (* 1.2053 T) (* 0.4992 T T))))
432
433 (defun solar-equinoxes/solstices (k year)
434 "Date of equinox/solstice K for YEAR. K=0, spring equinox; K=1, summer
435 solstice; K=2, fall equinox; K=3, winter solstice. Accurate to within
436 several minutes."
437 (let ((date (list (+ 3 (* k 3)) 21 year))
438 app
439 (correction 1000))
440 (while (> correction 0.00001)
441 (setq app (mod (solar-apparent-longitude-of-sun date) 360))
442 (setq correction (* 58 (solar-sin-degrees (- (* k 90) app))))
443 (setq date (list (extract-calendar-month date)
444 (+ (extract-calendar-day date) correction)
445 year)))
446 (list (extract-calendar-month date)
447 (+ (extract-calendar-day date) (/ calendar-time-zone 60.0 24.0)
448 (- (/ (solar-ephemeris-correction year) 60.0 24.0)))
449 year)))
450
451 ;;;###autoload
452 (defun sunrise-sunset (&optional arg)
453 "Local time of sunrise and sunset for today. Accurate to +/- 2 minutes.
454 If called with an optional prefix argument, prompt for date.
455
456 If called with an optional double prefix argument, prompt for longitude,
457 latitude, time zone, and date, and always use standard time.
458
459 This function is suitable for execution in a .emacs file."
460 (interactive "p")
461 (or arg (setq arg 1))
462 (if (and (< arg 16)
463 (not (and calendar-latitude calendar-longitude calendar-time-zone)))
464 (solar-setup))
465 (let* ((calendar-longitude
466 (if (< arg 16) calendar-longitude
467 (solar-get-number
468 "Enter longitude (decimal fraction; + east, - west): ")))
469 (calendar-latitude
470 (if (< arg 16) calendar-latitude
471 (solar-get-number
472 "Enter latitude (decimal fraction; + north, - south): ")))
473 (calendar-time-zone
474 (if (< arg 16) calendar-time-zone
475 (solar-get-number
476 "Enter difference from Coordinated Universal Time (in minutes): ")))
477 (calendar-location-name
478 (if (< arg 16) calendar-location-name
479 (let ((float-output-format "%.1f"))
480 (format "%s%s, %s%s"
481 (if (numberp calendar-latitude)
482 (abs calendar-latitude)
483 (+ (aref calendar-latitude 0)
484 (/ (aref calendar-latitude 1) 60.0)))
485 (if (numberp calendar-latitude)
486 (if (> calendar-latitude 0) "N" "S")
487 (if (equal (aref calendar-latitude 2) 'north) "N" "S"))
488 (if (numberp calendar-longitude)
489 (abs calendar-longitude)
490 (+ (aref calendar-longitude 0)
491 (/ (aref calendar-longitude 1) 60.0)))
492 (if (numberp calendar-longitude)
493 (if (> calendar-longitude 0) "E" "W")
494 (if (equal (aref calendar-latitude 2) 'east)
495 "E" "W"))))))
496 (calendar-standard-time-zone-name
497 (if (< arg 16) calendar-standard-time-zone-name
498 (cond ((= calendar-time-zone 0) "UTC")
499 ((< calendar-time-zone 0)
500 (format "UTC%dmin" calendar-time-zone))
501 (t (format "UTC+%dmin" calendar-time-zone)))))
502 (calendar-daylight-savings-starts
503 (if (< arg 16) calendar-daylight-savings-starts))
504 (calendar-daylight-savings-ends
505 (if (< arg 16) calendar-daylight-savings-ends))
506 (date (if (< arg 4) (calendar-current-date) (calendar-read-date)))
507 (date-string (calendar-date-string date t))
508 (time-string (solar-sunrise-sunset date))
509 (msg (format "%s: %s" date-string time-string))
510 (one-window (one-window-p t)))
511 (if (<= (length msg) (frame-width))
512 (message msg)
513 (with-output-to-temp-buffer "*temp*"
514 (princ (concat date-string "\n" time-string)))
515 (message (substitute-command-keys
516 (if one-window
517 (if pop-up-windows
518 "Type \\[delete-other-windows] to remove temp window."
519 "Type \\[switch-to-buffer] RET to remove temp window.")
520 "Type \\[switch-to-buffer-other-window] RET to restore old contents of temp window."))))))
521
522 (defun calendar-sunrise-sunset ()
523 "Local time of sunrise and sunset for date under cursor.
524 Accurate to +/- 2 minutes."
525 (interactive)
526 (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
527 (solar-setup))
528 (let ((date (calendar-cursor-to-date t)))
529 (message "%s: %s"
530 (calendar-date-string date t t)
531 (solar-sunrise-sunset date))))
532
533 (defun diary-sunrise-sunset ()
534 "Local time of sunrise and sunset as a diary entry.
535 Accurate to +/- 2 minutes."
536 (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
537 (solar-setup))
538 (solar-sunrise-sunset date))
539
540 (defun diary-sabbath-candles ()
541 "Local time of candle lighting diary entry--applies if date is a Friday.
542 No diary entry if there is no sunset on that date."
543 (if (not (and calendar-latitude calendar-longitude calendar-time-zone))
544 (solar-setup))
545 (if (= (% (calendar-absolute-from-gregorian date) 7) 5);; Friday
546 (let* ((sunset (solar-sunset date))
547 (light (if sunset
548 (solar-adj-time-for-dst
549 date
550 (- sunset (/ 18.0 60.0))))))
551 (if (and light (calendar-date-equal date (car light)))
552 (format "%s Sabbath candle lighting"
553 (apply 'solar-time-string (cdr light)))))))
554
555 ;;;###autoload
556 (defun solar-equinoxes-solstices ()
557 "Date and time of equinoxes and solstices, if visible in the calendar window.
558 Requires floating point."
559 (let ((m displayed-month)
560 (y displayed-year))
561 (increment-calendar-month m y (cond ((= 1 (% m 3)) -1)
562 ((= 2 (% m 3)) 1)
563 (t 0)))
564 (let* ((calendar-standard-time-zone-name
565 (if calendar-time-zone calendar-standard-time-zone-name "UTC"))
566 (calendar-daylight-savings-starts
567 (if calendar-time-zone calendar-daylight-savings-starts))
568 (calendar-daylight-savings-ends
569 (if calendar-time-zone calendar-daylight-savings-ends))
570 (calendar-time-zone (if calendar-time-zone calendar-time-zone 0))
571 (k (1- (/ m 3)))
572 (date (solar-equinoxes/solstices k y))
573 (s-hemi (and calendar-latitude (< (calendar-latitude) 0)))
574 (day (extract-calendar-day date))
575 (adj (solar-adj-time-for-dst
576 (list (extract-calendar-month date)
577 (truncate day)
578 (extract-calendar-year date))
579 (* 24 (- day (truncate day))))))
580 (list (list (car adj)
581 (format "%s %s"
582 (nth k (if s-hemi solar-s-hemi-seasons
583 solar-n-hemi-seasons))
584 (apply 'solar-time-string (cdr adj))))))))
585
586 (provide 'solar)
587
588 ;;; solar.el ends here