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