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   1  ;;; lunar.el --- calendar functions for phases of the moon.
   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: moon, lunar phases, calendar, diary
   8  
   9  ;; This file is part of XEmacs.
  10  
  11  ;; XEmacs is free software; you can redistribute it and/or modify it
  12  ;; under the terms of the GNU General Public License as published by
  13  ;; the Free Software Foundation; either version 2, or (at your option)
  14  ;; any later version.
  15  
  16  ;; XEmacs is distributed in the hope that it will be useful, but
  17  ;; WITHOUT ANY WARRANTY; without even the implied warranty of
  18  ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  ;; General Public License for more details.
  20  
  21  ;; You should have received a copy of the GNU General Public License
  22  ;; along with XEmacs; see the file COPYING.  If not, write to the Free
  23  ;; Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  24  
  25  ;;; Commentary:
  26  
  27  ;; This collection of functions implements lunar phases for calendar.el and
  28  ;; diary.el.
  29  
  30  ;; Based on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
  31  ;; Willmann-Bell, Inc., 1985.
  32  ;;
  33  ;; WARNING: The calculations will be accurate only to within a few minutes.
  34  
  35  ;; The author would be delighted to have an astronomically more sophisticated
  36  ;; person rewrite the code for the lunar calculations in this file!
  37  
  38  ;; Comments, corrections, and improvements should be sent to
  39  ;;  Edward M. Reingold               Department of Computer Science
  40  ;;  (217) 333-6733                   University of Illinois at Urbana-Champaign
  41  ;;  reingold@cs.uiuc.edu             1304 West Springfield Avenue
  42  ;;                                   Urbana, Illinois 61801
  43  
  44  ;;; Code:
  45  
  46  ;(if (fboundp 'atan)
  47  ;    (require 'lisp-float-type)
  48  ;  (error "Lunar calculations impossible since floating point is unavailable."))
  49  
  50  ;(require 'solar)
  51  
  52  (defun lunar-phase-list (month year)
  53    "List of lunar phases for three months starting with Gregorian MONTH, YEAR."
  54    (let ((end-month month)
  55          (end-year year)
  56          (start-month month)
  57          (start-year year))
  58      (increment-calendar-month end-month end-year 3)
  59      (increment-calendar-month start-month start-year -1)
  60      (let* ((end-date (list (list end-month 1 end-year)))
  61             (start-date (list (list start-month 
  62                                     (calendar-last-day-of-month
  63                                      start-month start-year)
  64                                     start-year)))
  65             (index (* 4
  66                       (truncate
  67                        (* 12.3685
  68                           (+ year
  69                              ( / (calendar-day-number (list month 1 year))
  70                                  366.0)
  71                              -1900)))))
  72             (new-moon (lunar-phase index))
  73             (list))
  74        (while (calendar-date-compare new-moon end-date)
  75          (if (calendar-date-compare start-date new-moon)
  76              (setq list (append list (list new-moon))))
  77          (setq index (1+ index))
  78          (setq new-moon (lunar-phase index)))
  79        list)))
  80  
  81  (defun lunar-phase (index)
  82    "Local date and time of lunar phase INDEX.
  83  Integer below INDEX/4 gives the lunation number, counting from Jan 1, 1900;
  84  remainder mod 4 gives the phase: 0 new moon, 1 first quarter, 2 full moon,
  85  3 last quarter."
  86    (let* ((phase (mod index 4))
  87           (index (/ index 4.0))
  88           (time (/ index 1236.85))
  89           (date (+ (calendar-absolute-from-gregorian '(1 0.5 1900))
  90                    0.75933
  91                    (* 29.53058868 index)
  92                    (* 0.0001178 time time)
  93                    (* -0.000000155 time time time)
  94                    (* 0.00033
  95                       (solar-sin-degrees (+ 166.56
  96                                             (* 132.87 time)
  97                                             (* -0.009173 time time))))))
  98           (sun-anomaly (mod
  99                         (+ 359.2242
 100                            (* 29.105356 index)
 101                            (* -0.0000333 time time)
 102                            (* -0.00000347 time time time))
 103                         360.0))
 104           (moon-anomaly (mod
 105                          (+ 306.0253
 106                             (* 385.81691806 index)
 107                             (* 0.0107306 time time)
 108                             (* 0.00001236 time time time))
 109                          360.0))
 110           (moon-lat (mod
 111                      (+ 21.2964
 112                         (* 390.67050646 index)
 113                         (* -0.0016528 time time)
 114                         (* -0.00000239 time time time))
 115                      360.0))
 116           (adjustment
 117            (if (memq phase '(0 2))
 118                (+ (* (- 0.1734 (* 0.000393 time))
 119                      (solar-sin-degrees sun-anomaly))
 120                   (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
 121                   (* -0.4068 (solar-sin-degrees moon-anomaly))
 122                   (* 0.0161 (solar-sin-degrees (* 2 moon-anomaly)))
 123                   (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
 124                   (* 0.0104 (solar-sin-degrees (* 2 moon-lat)))
 125                   (* -0.0051 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
 126                   (* -0.0074 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
 127                   (* 0.0004 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
 128                   (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
 129                   (* -0.0006 (solar-sin-degrees
 130                               (+ (* 2 moon-lat) moon-anomaly)))
 131                   (* 0.0010 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
 132                   (* 0.0005 (solar-sin-degrees
 133                              (+ (* 2 moon-anomaly) sun-anomaly))))
 134              (+ (* (- 0.1721 (* 0.0004 time))
 135                    (solar-sin-degrees sun-anomaly))
 136                 (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
 137                 (* -0.6280 (solar-sin-degrees moon-anomaly))
 138                 (* 0.0089 (solar-sin-degrees (* 2 moon-anomaly)))
 139                 (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
 140                 (* 0.0079 (solar-sin-degrees (* 2 moon-lat)))
 141                 (* -0.0119 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
 142                 (* -0.0047 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
 143                 (* 0.0003 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
 144                 (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
 145                 (* -0.0006 (solar-sin-degrees (+ (* 2 moon-lat) moon-anomaly)))
 146                 (* 0.0021 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
 147                 (* 0.0003 (solar-sin-degrees
 148                            (+ (* 2 moon-anomaly) sun-anomaly)))
 149                 (* 0.0004 (solar-sin-degrees
 150                            (- sun-anomaly (* 2 moon-anomaly))))
 151                 (* -0.0003 (solar-sin-degrees
 152                            (+ (* 2 sun-anomaly) moon-anomaly))))))
 153           (adj (+ 0.0028
 154                   (* -0.0004 (solar-cosine-degrees
 155                               sun-anomaly))
 156                   (* 0.0003 (solar-cosine-degrees
 157                              moon-anomaly))))
 158           (adjustment (cond ((= phase 1) (+ adjustment adj))
 159                             ((= phase 2) (- adjustment adj))
 160                             (t adjustment)))
 161           (date (+ date adjustment))
 162       (date (+ date (/ (- calendar-time-zone
 163                   (solar-ephemeris-correction
 164                                (extract-calendar-year
 165                                 (calendar-gregorian-from-absolute
 166                                  (truncate date)))))
 167                60.0 24.0)))
 168           (time (* 24 (- date (truncate date))))
 169       (date (calendar-gregorian-from-absolute (truncate date)))
 170           (adj (solar-adj-time-for-dst date time)))
 171      (list (car adj) (apply 'solar-time-string (cdr adj)) phase)))
 172  
 173  (defun lunar-phase-name (phase)
 174    "Name of lunar PHASE.
 175  0 = new moon, 1 = first quarter, 2 = full moon, 3 = last quarter."
 176    (cond ((= 0 phase) "New Moon")
 177          ((= 1 phase) "First Quarter Moon")
 178          ((= 2 phase) "Full Moon")
 179          ((= 3 phase) "Last Quarter Moon")))
 180  
 181  (defun calendar-phases-of-moon ()
 182    "Create a buffer with the lunar phases for the current calendar window."
 183    (interactive)
 184    (message "Computing phases of the moon...")
 185    (let ((m1 displayed-month)
 186          (y1 displayed-year)
 187          (m2 displayed-month)
 188          (y2 displayed-year))
 189      (increment-calendar-month m1 y1 -1)
 190      (increment-calendar-month m2 y2 1)
 191      (set-buffer (get-buffer-create lunar-phases-buffer))
 192      (setq buffer-read-only nil)
 193      (calendar-set-mode-line
 194       (if (= y1 y2)
 195           (format "Phases of the Moon from %s to %s, %d%%-"
 196                   (calendar-month-name m1) (calendar-month-name m2) y2)
 197         (format "Phases of the Moon from %s, %d to %s, %d%%-"
 198                 (calendar-month-name m1) y1 (calendar-month-name m2) y2)))
 199      (erase-buffer)
 200      (insert
 201       (mapconcat
 202        '(lambda (x)
 203           (let ((date (car x))
 204                 (time (car (cdr x)))
 205                 (phase (car (cdr (cdr x)))))
 206             (concat (calendar-date-string date)
 207                     ": "
 208                     (lunar-phase-name phase)
 209                     " "
 210                     time)))
 211        (lunar-phase-list m1 y1) "\n"))
 212      (goto-char (point-min))
 213      (set-buffer-modified-p nil)
 214      (setq buffer-read-only t)
 215      (display-buffer lunar-phases-buffer)
 216      (message "Computing phases of the moon...done")))
 217  
 218  ;;;###autoload
 219  (defun phases-of-moon (&optional arg)
 220    "Display the quarters of the moon for last month, this month, and next month.
 221  If called with an optional prefix argument, prompts for month and year.
 222  
 223  This function is suitable for execution in a .emacs file."
 224    (interactive "P")
 225    (save-excursion
 226      (let* ((date (if arg
 227                       (calendar-read-date t)
 228                     (calendar-current-date)))
 229             (displayed-month (extract-calendar-month date))
 230             (displayed-year (extract-calendar-year date)))
 231        (calendar-phases-of-moon))))
 232  
 233  (defun diary-phases-of-moon ()
 234    "Moon phases diary entry."
 235    (let* ((index (* 4
 236                     (truncate
 237                      (* 12.3685
 238                         (+ (extract-calendar-year date)
 239                            ( / (calendar-day-number date)
 240                                366.0)
 241                            -1900)))))
 242           (phase (lunar-phase index)))
 243      (while (calendar-date-compare phase (list date))
 244        (setq index (1+ index))
 245        (setq phase (lunar-phase index)))
 246      (if (calendar-date-equal (car phase) date)
 247          (concat (lunar-phase-name (car (cdr (cdr phase)))) " "
 248                  (car (cdr phase))))))
 249  
 250  ;(provide 'lunar)
 251  
 252  ;;; lunar.el ends here