code.delx.au - gnu-emacs/blob - lisp/calendar/lunar.el

   1 ;;; lunar.el --- calendar functions for phases of the moon.
   2
   3 ;; Copyright (C) 1992 Free Software Foundation, Inc.
   4
   5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
   6 ;; Keywords: calendar
   7 ;; Human-Keywords: moon, lunar phases, calendar, diary
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is distributed in the hope that it will be useful,
  12 ;; but WITHOUT ANY WARRANTY.  No author or distributor
  13 ;; accepts responsibility to anyone for the consequences of using it
  14 ;; or for whether it serves any particular purpose or works at all,
  15 ;; unless he says so in writing.  Refer to the GNU Emacs General Public
  16 ;; License for full details.
  17
  18 ;; Everyone is granted permission to copy, modify and redistribute
  19 ;; GNU Emacs, but only under the conditions described in the
  20 ;; GNU Emacs General Public License.   A copy of this license is
  21 ;; supposed to have been given to you along with GNU Emacs so you
  22 ;; can know your rights and responsibilities.  It should be in a
  23 ;; file named COPYING.  Among other things, the copyright notice
  24 ;; and this notice must be preserved on all copies.
  25
  26 ;;; Commentary:
  27
  28 ;; This collection of functions implements lunar phases for calendar.el and
  29 ;; diary.el.
  30
  31 ;; Based on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
  32 ;; Willmann-Bell, Inc., 1985.
  33 ;;
  34 ;; WARNING: The calculations will be accurate only to within a few minutes.
  35
  36 ;; The author would be delighted to have an astronomically more sophisticated
  37 ;; person rewrite the code for the lunar calculations in this file!
  38
  39 ;; Comments, corrections, and improvements should be sent to
  40 ;;  Edward M. Reingold               Department of Computer Science
  41 ;;  (217) 333-6733                   University of Illinois at Urbana-Champaign
  42 ;;  reingold@cs.uiuc.edu             1304 West Springfield Avenue
  43 ;;                                   Urbana, Illinois 61801
  44
  45 ;;; Code:
  46
  47 (if (fboundp 'atan)
  48     (require 'lisp-float-type)
  49   (error "Lunar calculations impossible since floating point is unavailable."))
  50
  51 (require 'solar)
  52
  53 (defun lunar-phase-list (month year)
  54   "List of lunar phases for three months starting with Gregorian MONTH, YEAR."
  55   (let ((end-month month)
  56         (end-year year)
  57         (start-month month)
  58         (start-year year))
  59     (increment-calendar-month end-month end-year 3)
  60     (increment-calendar-month start-month start-year -1)
  61     (let* ((end-date (list (list end-month 1 end-year)))
  62            (start-date (list (list start-month
  63                                    (calendar-last-day-of-month
  64                                     start-month start-year)
  65                                    start-year)))
  66            (index (* 4
  67                      (truncate
  68                       (* 12.3685
  69                          (+ year
  70                             ( / (calendar-day-number (list month 1 year))
  71                                 366.0)
  72                             -1900)))))
  73            (new-moon (lunar-phase index))
  74            (list))
  75       (while (calendar-date-compare new-moon end-date)
  76         (if (calendar-date-compare start-date new-moon)
  77             (setq list (append list (list new-moon))))
  78         (setq index (1+ index))
  79         (setq new-moon (lunar-phase index)))
  80       list)))
  81
  82 (defun lunar-phase (index)
  83   "Local date and time of lunar phase INDEX.
  84 Integer below INDEX/4 gives the lunation number, counting from Jan 1, 1900;
  85 remainder mod 4 gives the phase: 0 new moon, 1 first quarter, 2 full moon,
  86 3 last quarter."
  87   (let* ((phase (% index 4))
  88          (index (/ index 4.0))
  89          (time (/ index 1236.85))
  90          (date (+ (calendar-absolute-from-gregorian '(1 0.5 1900))
  91                   0.75933
  92                   (* 29.53058868 index)
  93                   (* 0.0001178 time time)
  94                   (* -0.000000155 time time time)
  95                   (* 0.00033
  96                      (solar-sin-degrees (+ 166.56
  97                                            (* 132.87 time)
  98                                            (* -0.009173 time time))))))
  99          (sun-anomaly (solar-mod
 100                        (+ 359.2242
 101                           (* 29.105356 index)
 102                           (* -0.0000333 time time)
 103                           (* -0.00000347 time time time))
 104                        360.0))
 105          (moon-anomaly (solar-mod
 106                         (+ 306.0253
 107                            (* 385.81691806 index)
 108                            (* 0.0107306 time time)
 109                            (* 0.00001236 time time time))
 110                         360.0))
 111          (moon-lat (solar-mod
 112                     (+ 21.2964
 113                        (* 390.67050646 index)
 114                        (* -0.0016528 time time)
 115                        (* -0.00000239 time time time))
 116                     360.0))
 117          (adjustment
 118           (if (memq phase '(0 2))
 119               (+ (* (- 0.1734 (* 0.000393 time))
 120                     (solar-sin-degrees sun-anomaly))
 121                  (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
 122                  (* -0.4068 (solar-sin-degrees moon-anomaly))
 123                  (* 0.0161 (solar-sin-degrees (* 2 moon-anomaly)))
 124                  (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
 125                  (* 0.0104 (solar-sin-degrees (* 2 moon-lat)))
 126                  (* -0.0051 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
 127                  (* -0.0074 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
 128                  (* 0.0004 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
 129                  (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
 130                  (* -0.0006 (solar-sin-degrees
 131                              (+ (* 2 moon-lat) moon-anomaly)))
 132                  (* 0.0010 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
 133                  (* 0.0005 (solar-sin-degrees
 134                             (+ (* 2 moon-anomaly) sun-anomaly))))
 135             (+ (* (- 0.1721 (* 0.0004 time))
 136                   (solar-sin-degrees sun-anomaly))
 137                (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
 138                (* -0.6280 (solar-sin-degrees moon-anomaly))
 139                (* 0.0089 (solar-sin-degrees (* 2 moon-anomaly)))
 140                (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
 141                (* 0.0079 (solar-sin-degrees (* 2 moon-lat)))
 142                (* -0.0119 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
 143                (* -0.0047 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
 144                (* 0.0003 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
 145                (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
 146                (* -0.0006 (solar-sin-degrees (+ (* 2 moon-lat) moon-anomaly)))
 147                (* 0.0021 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
 148                (* 0.0003 (solar-sin-degrees
 149                           (+ (* 2 moon-anomaly) sun-anomaly)))
 150                (* 0.0004 (solar-sin-degrees
 151                           (- sun-anomaly (* 2 moon-anomaly))))
 152                (* -0.0003 (solar-sin-degrees
 153                           (+ (* 2 sun-anomaly) moon-anomaly))))))
 154          (adj (+ 0.0028
 155                  (* -0.0004 (solar-cosine-degrees
 156                              sun-anomaly))
 157                  (* 0.0003 (solar-cosine-degrees
 158                             moon-anomaly))))
 159          (adjustment (cond ((= phase 1) (+ adjustment adj))
 160                            ((= phase 2) (- adjustment adj))
 161                            (t adjustment)))
 162          (date (+ date adjustment))
 163          (date (+ date (- (/ (solar-ephemeris-correction
 164                               (extract-calendar-year
 165                                (calendar-gregorian-from-absolute
 166                                 (truncate date)))) 60.0 24.0))))
 167          (time (* 24 (- date (truncate date))))
 168          (date (calendar-gregorian-from-absolute (truncate date))))
 169     (list date (solar-time-string time date) phase)))
 170
 171 (defun lunar-phase-name (phase)
 172   "Name of lunar PHASE.
 173 0 = new moon, 1 = first quarter, 2 = full moon, 3 = last quarter."
 174   (cond ((= 0 phase) "New Moon")
 175         ((= 1 phase) "First Quarter Moon")
 176         ((= 2 phase) "Full Moon")
 177         ((= 3 phase) "Last Quarter Moon")))
 178
 179 (defun calendar-phases-of-moon ()
 180   "Create a buffer with the lunar phases for the current calendar window."
 181   (interactive)
 182   (message "Computing phases of the moon...")
 183   (let ((m1 displayed-month)
 184         (y1 displayed-year)
 185         (m2 displayed-month)
 186         (y2 displayed-year)
 187         (lunar-phases-buffer "*Phases of Moon*"))
 188     (increment-calendar-month m1 y1 -1)
 189     (increment-calendar-month m2 y2 1)
 190     (set-buffer (get-buffer-create lunar-phases-buffer))
 191     (setq buffer-read-only nil)
 192     (calendar-set-mode-line
 193           (format "Phases of the moon from %s, %d to %s, %d%%-"
 194                   (calendar-month-name m1) y1 (calendar-month-name m2) y2))
 195     (erase-buffer)
 196     (insert
 197      (mapconcat
 198       '(lambda (x)
 199          (let ((date (car x))
 200                (time (car (cdr x)))
 201                (phase (car (cdr (cdr x)))))
 202            (concat (calendar-date-string date)
 203                    ": "
 204                    (lunar-phase-name phase)
 205                    " "
 206                    time)))
 207       (lunar-phase-list m1 y1) "\n"))
 208     (goto-char (point-min))
 209     (set-buffer-modified-p nil)
 210     (setq buffer-read-only t)
 211     (display-buffer lunar-phases-buffer)
 212     (message "Computing phases of the moon...done")))
 213
 214 ;;;###autoload
 215 (defun phases-of-moon (&optional arg)
 216   "Display the quarters of the moon for last month, this month, and next month.
 217 If called with an optional prefix argument, prompts for month and year.
 218
 219 This function is suitable for execution in a .emacs file."
 220   (interactive "P")
 221   (save-excursion
 222     (let* ((completion-ignore-case t)
 223            (date (calendar-current-date))
 224            (displayed-month
 225             (if arg
 226                 (cdr (assoc
 227                       (capitalize
 228                        (completing-read
 229                         "Month name: "
 230                         (mapcar 'list (append calendar-month-name-array nil))
 231                         nil t))
 232                       (calendar-make-alist calendar-month-name-array)))
 233               (extract-calendar-month date)))
 234            (displayed-year
 235             (if arg
 236                 (calendar-read
 237                  "Year (>0): "
 238                  '(lambda (x) (> x 0))
 239                  (int-to-string
 240                   (extract-calendar-year (calendar-current-date))))
 241               (extract-calendar-year date))))
 242       (calendar-phases-of-moon))))
 243
 244 (defun diary-phases-of-moon ()
 245   "Moon phases diary entry."
 246   (let* ((index (* 4
 247                    (truncate
 248                     (* 12.3685
 249                        (+ (extract-calendar-year date)
 250                           ( / (calendar-day-number date)
 251                               366.0)
 252                           -1900)))))
 253          (phase (lunar-phase index)))
 254     (while (calendar-date-compare phase (list date))
 255       (setq index (1+ index))
 256       (setq phase (lunar-phase index)))
 257     (if (calendar-date-equal (car phase) date)
 258         (concat (lunar-phase-name (car (cdr (cdr phase)))) " "
 259                 (car (cdr phase))))))
 260
 261 (provide 'lunar)
 262
 263 ;;; lunar.el ends here