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