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1 ;;; lunar.el --- calendar functions for phases of the moon.
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2
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3 ;; Copyright (C) 1992, 1993 Free Software Foundation, Inc.
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4
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5 ;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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6 ;; Keywords: calendar
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7 ;; Human-Keywords: moon, lunar phases, calendar, diary
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8
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9 ;; This file is part of XEmacs.
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10
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11 ;; XEmacs is free software; you can redistribute it and/or modify it
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12 ;; under the terms of the GNU General Public License as published by
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13 ;; the Free Software Foundation; either version 2, or (at your option)
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14 ;; any later version.
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15
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16 ;; XEmacs is distributed in the hope that it will be useful, but
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17 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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19 ;; General Public License for more details.
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20
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21 ;; You should have received a copy of the GNU General Public License
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16
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22 ;; along with XEmacs; see the file COPYING. If not, write to the
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23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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24 ;; Boston, MA 02111-1307, USA.
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25
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26 ;;; Commentary:
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27
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28 ;; This collection of functions implements lunar phases for calendar.el and
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29 ;; diary.el.
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30
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31 ;; Based on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
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32 ;; Willmann-Bell, Inc., 1985.
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33 ;;
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34 ;; WARNING: The calculations will be accurate only to within a few minutes.
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35
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36 ;; The author would be delighted to have an astronomically more sophisticated
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37 ;; person rewrite the code for the lunar calculations in this file!
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38
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39 ;; Comments, corrections, and improvements should be sent to
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40 ;; Edward M. Reingold Department of Computer Science
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41 ;; (217) 333-6733 University of Illinois at Urbana-Champaign
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42 ;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
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43 ;; Urbana, Illinois 61801
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44
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45 ;;; Code:
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46
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47 (if (fboundp 'atan)
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48 (require 'lisp-float-type)
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49 (error "Lunar calculations impossible since floating point is unavailable."))
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50
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51 (require 'solar)
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52
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53 (defun lunar-phase-list (month year)
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54 "List of lunar phases for three months starting with Gregorian MONTH, YEAR."
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55 (let ((end-month month)
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56 (end-year year)
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57 (start-month month)
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58 (start-year year))
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59 (increment-calendar-month end-month end-year 3)
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60 (increment-calendar-month start-month start-year -1)
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61 (let* ((end-date (list (list end-month 1 end-year)))
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62 (start-date (list (list start-month
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63 (calendar-last-day-of-month
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64 start-month start-year)
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65 start-year)))
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66 (index (* 4
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67 (truncate
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68 (* 12.3685
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69 (+ year
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70 ( / (calendar-day-number (list month 1 year))
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71 366.0)
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72 -1900)))))
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73 (new-moon (lunar-phase index))
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74 (list))
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75 (while (calendar-date-compare new-moon end-date)
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76 (if (calendar-date-compare start-date new-moon)
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77 (setq list (append list (list new-moon))))
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78 (setq index (1+ index))
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79 (setq new-moon (lunar-phase index)))
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80 list)))
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81
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82 (defun lunar-phase (index)
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83 "Local date and time of lunar phase INDEX.
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84 Integer below INDEX/4 gives the lunation number, counting from Jan 1, 1900;
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85 remainder mod 4 gives the phase: 0 new moon, 1 first quarter, 2 full moon,
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86 3 last quarter."
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87 (let* ((phase (mod index 4))
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88 (index (/ index 4.0))
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89 (time (/ index 1236.85))
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90 (date (+ (calendar-absolute-from-gregorian '(1 0.5 1900))
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91 0.75933
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92 (* 29.53058868 index)
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93 (* 0.0001178 time time)
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94 (* -0.000000155 time time time)
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95 (* 0.00033
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96 (solar-sin-degrees (+ 166.56
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97 (* 132.87 time)
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98 (* -0.009173 time time))))))
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99 (sun-anomaly (mod
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100 (+ 359.2242
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101 (* 29.105356 index)
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102 (* -0.0000333 time time)
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103 (* -0.00000347 time time time))
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104 360.0))
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105 (moon-anomaly (mod
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106 (+ 306.0253
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107 (* 385.81691806 index)
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108 (* 0.0107306 time time)
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109 (* 0.00001236 time time time))
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110 360.0))
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111 (moon-lat (mod
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112 (+ 21.2964
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113 (* 390.67050646 index)
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114 (* -0.0016528 time time)
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115 (* -0.00000239 time time time))
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116 360.0))
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117 (adjustment
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118 (if (memq phase '(0 2))
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119 (+ (* (- 0.1734 (* 0.000393 time))
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120 (solar-sin-degrees sun-anomaly))
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121 (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
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122 (* -0.4068 (solar-sin-degrees moon-anomaly))
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123 (* 0.0161 (solar-sin-degrees (* 2 moon-anomaly)))
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124 (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
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125 (* 0.0104 (solar-sin-degrees (* 2 moon-lat)))
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126 (* -0.0051 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
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127 (* -0.0074 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
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128 (* 0.0004 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
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129 (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
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130 (* -0.0006 (solar-sin-degrees
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131 (+ (* 2 moon-lat) moon-anomaly)))
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132 (* 0.0010 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
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133 (* 0.0005 (solar-sin-degrees
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134 (+ (* 2 moon-anomaly) sun-anomaly))))
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135 (+ (* (- 0.1721 (* 0.0004 time))
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136 (solar-sin-degrees sun-anomaly))
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137 (* 0.0021 (solar-sin-degrees (* 2 sun-anomaly)))
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138 (* -0.6280 (solar-sin-degrees moon-anomaly))
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139 (* 0.0089 (solar-sin-degrees (* 2 moon-anomaly)))
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140 (* -0.0004 (solar-sin-degrees (* 3 moon-anomaly)))
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141 (* 0.0079 (solar-sin-degrees (* 2 moon-lat)))
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142 (* -0.0119 (solar-sin-degrees (+ sun-anomaly moon-anomaly)))
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143 (* -0.0047 (solar-sin-degrees (- sun-anomaly moon-anomaly)))
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144 (* 0.0003 (solar-sin-degrees (+ (* 2 moon-lat) sun-anomaly)))
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145 (* -0.0004 (solar-sin-degrees (- (* 2 moon-lat) sun-anomaly)))
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146 (* -0.0006 (solar-sin-degrees (+ (* 2 moon-lat) moon-anomaly)))
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147 (* 0.0021 (solar-sin-degrees (- (* 2 moon-lat) moon-anomaly)))
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148 (* 0.0003 (solar-sin-degrees
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149 (+ (* 2 moon-anomaly) sun-anomaly)))
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150 (* 0.0004 (solar-sin-degrees
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151 (- sun-anomaly (* 2 moon-anomaly))))
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152 (* -0.0003 (solar-sin-degrees
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153 (+ (* 2 sun-anomaly) moon-anomaly))))))
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154 (adj (+ 0.0028
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155 (* -0.0004 (solar-cosine-degrees
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156 sun-anomaly))
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157 (* 0.0003 (solar-cosine-degrees
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158 moon-anomaly))))
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159 (adjustment (cond ((= phase 1) (+ adjustment adj))
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160 ((= phase 2) (- adjustment adj))
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161 (t adjustment)))
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162 (date (+ date adjustment))
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163 (date (+ date (/ (- calendar-time-zone
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164 (solar-ephemeris-correction
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165 (extract-calendar-year
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166 (calendar-gregorian-from-absolute
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167 (truncate date)))))
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168 60.0 24.0)))
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169 (time (* 24 (- date (truncate date))))
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170 (date (calendar-gregorian-from-absolute (truncate date)))
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171 (adj (solar-adj-time-for-dst date time)))
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172 (list (car adj) (apply 'solar-time-string (cdr adj)) phase)))
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173
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174 (defun lunar-phase-name (phase)
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175 "Name of lunar PHASE.
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176 0 = new moon, 1 = first quarter, 2 = full moon, 3 = last quarter."
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177 (cond ((= 0 phase) "New Moon")
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178 ((= 1 phase) "First Quarter Moon")
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179 ((= 2 phase) "Full Moon")
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180 ((= 3 phase) "Last Quarter Moon")))
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181
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182 (defun calendar-phases-of-moon ()
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183 "Create a buffer with the lunar phases for the current calendar window."
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184 (interactive)
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185 (message "Computing phases of the moon...")
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186 (let ((m1 displayed-month)
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187 (y1 displayed-year)
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188 (m2 displayed-month)
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189 (y2 displayed-year))
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190 (increment-calendar-month m1 y1 -1)
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191 (increment-calendar-month m2 y2 1)
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192 (set-buffer (get-buffer-create lunar-phases-buffer))
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193 (setq buffer-read-only nil)
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194 (calendar-set-mode-line
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195 (if (= y1 y2)
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196 (format "Phases of the Moon from %s to %s, %d%%-"
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197 (calendar-month-name m1) (calendar-month-name m2) y2)
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198 (format "Phases of the Moon from %s, %d to %s, %d%%-"
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199 (calendar-month-name m1) y1 (calendar-month-name m2) y2)))
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200 (erase-buffer)
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201 (insert
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202 (mapconcat
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203 '(lambda (x)
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204 (let ((date (car x))
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205 (time (car (cdr x)))
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206 (phase (car (cdr (cdr x)))))
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207 (concat (calendar-date-string date)
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208 ": "
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209 (lunar-phase-name phase)
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210 " "
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211 time)))
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212 (lunar-phase-list m1 y1) "\n"))
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213 (goto-char (point-min))
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214 (set-buffer-modified-p nil)
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215 (setq buffer-read-only t)
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216 (display-buffer lunar-phases-buffer)
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217 (message "Computing phases of the moon...done")))
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218
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219 ;;;###autoload
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220 (defun phases-of-moon (&optional arg)
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221 "Display the quarters of the moon for last month, this month, and next month.
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222 If called with an optional prefix argument, prompts for month and year.
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223
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224 This function is suitable for execution in a .emacs file."
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225 (interactive "P")
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226 (save-excursion
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227 (let* ((date (if arg
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228 (calendar-read-date t)
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229 (calendar-current-date)))
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230 (displayed-month (extract-calendar-month date))
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231 (displayed-year (extract-calendar-year date)))
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232 (calendar-phases-of-moon))))
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233
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234 (defun diary-phases-of-moon ()
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235 "Moon phases diary entry."
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236 (let* ((index (* 4
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237 (truncate
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238 (* 12.3685
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239 (+ (extract-calendar-year date)
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240 ( / (calendar-day-number date)
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241 366.0)
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242 -1900)))))
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243 (phase (lunar-phase index)))
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244 (while (calendar-date-compare phase (list date))
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245 (setq index (1+ index))
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246 (setq phase (lunar-phase index)))
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247 (if (calendar-date-equal (car phase) date)
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248 (concat (lunar-phase-name (car (cdr (cdr phase)))) " "
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249 (car (cdr phase))))))
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250
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251 (provide 'lunar)
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252
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253 ;;; lunar.el ends here
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