1992-08-12 12:49:57 +00:00
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;;; solar.el --- calendar functions for solar events.
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;; Copyright (C) 1992 Free Software Foundation, Inc.
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;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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1993-03-18 21:44:24 +00:00
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;; Keywords: calendar
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;; Human-Keywords: sunrise, sunset, equinox, solstice, calendar, diary,
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;; holidays
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1992-08-12 12:49:57 +00:00
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;; This file is part of GNU Emacs.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY. No author or distributor
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;; accepts responsibility to anyone for the consequences of using it
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;; or for whether it serves any particular purpose or works at all,
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;; unless he says so in writing. Refer to the GNU Emacs General Public
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;; License for full details.
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;; Everyone is granted permission to copy, modify and redistribute
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;; GNU Emacs, but only under the conditions described in the
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;; GNU Emacs General Public License. A copy of this license is
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;; supposed to have been given to you along with GNU Emacs so you
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;; can know your rights and responsibilities. It should be in a
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;; file named COPYING. Among other things, the copyright notice
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;; and this notice must be preserved on all copies.
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;;; Commentary:
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;; This collection of functions implements the features of calendar.el and
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1993-06-22 03:22:40 +00:00
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;; diary.el that deal with times of day, sunrise/sunset, and
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;; eqinoxes/solstices.
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1992-08-12 12:49:57 +00:00
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;; Based on the ``Almanac for Computers 1984,'' prepared by the Nautical
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;; Almanac Office, United States Naval Observatory, Washington, 1984 and
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;; on ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
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;; Willmann-Bell, Inc., 1985.
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;;
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;; WARNINGS:
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;; 1. SUNRISE/SUNSET calculations will be accurate only to +/- 2 minutes.
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;; Locations should be between +/- 65 degrees of latitude.
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;; Dates should be in the latter half of the 20th century.
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;;
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;; 2. Equinox/solstice times will be accurate only to +/- 15 minutes.
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;; The author would be delighted to have an astronomically more sophisticated
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;; person rewrite the code for the solar calculations in this file!
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;; Comments, corrections, and improvements should be sent to
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;; Edward M. Reingold Department of Computer Science
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;; (217) 333-6733 University of Illinois at Urbana-Champaign
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;; reingold@cs.uiuc.edu 1304 West Springfield Avenue
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;; Urbana, Illinois 61801
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;;; Code:
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(if (fboundp 'atan)
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(require 'lisp-float-type)
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(error "Solar calculations impossible since floating point is unavailable."))
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1993-06-22 03:22:40 +00:00
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(require 'cal-dst)
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;;;###autoload
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(defvar calendar-time-display-form
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'(12-hours ":" minutes am-pm
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(if time-zone " (") time-zone (if time-zone ")"))
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"*The pseudo-pattern that governs the way a time of day is formatted.
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A pseudo-pattern is a list of expressions that can involve the keywords
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`12-hours', `24-hours', and `minutes', all numbers in string form,
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and `am-pm' and `time-zone', both alphabetic strings.
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For example, the form
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'(24-hours \":\" minutes
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(if time-zone \" (\") time-zone (if time-zone \")\"))
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would give military-style times like `21:07 (UTC)'.")
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;;;###autoload
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(defvar calendar-latitude nil
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"*Latitude of `calendar-location-name' in degrees, + north, - south.
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1993-06-28 05:18:27 +00:00
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For example, 40.7 for New York City.
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It may not be a good idea to set this in advance for your site;
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if there may be users running Emacs at your site
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who are physically located elsewhere, they would get the wrong
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value and might not know how to override it.")
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1993-06-22 03:22:40 +00:00
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;;;###autoload
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(defvar calendar-longitude nil
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"*Longitude of `calendar-location-name' in degrees, + east, - west.
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1993-06-28 05:18:27 +00:00
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For example, -74.0 for New York City.
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It may not be a good idea to set this in advance for your site;
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if there may be users running Emacs at your site
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who are physically located elsewhere, they would get the wrong
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value and might not know how to override it.")
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1993-06-22 03:22:40 +00:00
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;;;###autoload
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(defvar calendar-location-name
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'(let ((float-output-format "%.1f"))
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(format "%s%s, %s%s"
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(abs calendar-latitude)
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(if (> calendar-latitude 0) "N" "S")
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(abs calendar-longitude)
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(if (> calendar-longitude 0) "E" "W")))
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"*Expression evaluating to name of `calendar-longitude', calendar-latitude'.
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Default value is just the latitude, longitude pair.")
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1992-08-12 12:49:57 +00:00
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(defun solar-setup ()
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"Prompt user for latitude, longitude, and time zone."
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(beep)
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(if (not calendar-longitude)
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(setq calendar-longitude
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(solar-get-number
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"Enter longitude (decimal fraction; + east, - west): ")))
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(if (not calendar-latitude)
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(setq calendar-latitude
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(solar-get-number
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"Enter latitude (decimal fraction; + north, - south): ")))
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(if (not calendar-time-zone)
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(setq calendar-time-zone
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(solar-get-number
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1993-06-16 23:12:21 +00:00
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"Enter difference from Coordinated Universal Time (in minutes): "))))
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1992-08-12 12:49:57 +00:00
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(defun solar-get-number (prompt)
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"Return a number from the minibuffer, prompting with PROMPT.
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Returns nil if nothing was entered."
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(let ((x (read-string prompt "")))
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(if (not (string-equal x ""))
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(string-to-int x))))
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(defun solar-sin-degrees (x)
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(sin (degrees-to-radians x)))
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(defun solar-cosine-degrees (x)
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(cos (degrees-to-radians x)))
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(defun solar-tangent-degrees (x)
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(tan (degrees-to-radians x)))
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(defun solar-xy-to-quadrant (x y)
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"Determines the quadrant of the point X, Y."
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(if (> x 0)
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(if (> y 0) 1 4)
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(if (> y 0) 2 3)))
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(defun solar-degrees-to-quadrant (angle)
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"Determines the quadrant of ANGLE."
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1993-08-10 04:14:17 +00:00
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(1+ (truncate (/ (mod angle 360.0) 90.0))))
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1992-08-12 12:49:57 +00:00
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(defun solar-arctan (x quad)
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"Arctangent of X in quadrant QUAD."
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(let ((deg (radians-to-degrees (atan x))))
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(cond ((equal quad 2) (+ deg 180))
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((equal quad 3) (+ deg 180))
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((equal quad 4) (+ deg 360))
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(t deg))))
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(defun solar-arccos (x)
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(let ((y (sqrt (- 1 (* x x)))))
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(solar-arctan (/ y x) (solar-xy-to-quadrant x y))))
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(defun solar-arcsin (y)
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(let ((x (sqrt (- 1 (* y y)))))
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(solar-arctan (/ y x) (solar-xy-to-quadrant x y))))
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(defconst solar-earth-inclination 23.441884
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"Inclination of earth's equator to its solar orbit in degrees.")
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(defconst solar-cos-inclination (solar-cosine-degrees solar-earth-inclination)
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"Cosine of earth's inclination.")
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(defconst solar-sin-inclination (solar-sin-degrees solar-earth-inclination)
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"Sine of earth's inclination.")
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(defconst solar-earth-orbit-eccentricity 0.016718
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"Eccentricity of orbit of the earth around the sun.")
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(defmacro solar-degrees-to-hours (deg)
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(list '/ deg 15))
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(defmacro solar-hours-to-days (hour)
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(list '/ hour 24))
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(defun solar-longitude-of-sun (day)
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"Longitude of the sun at DAY in the year."
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(let ((mean-anomaly (- (* 0.9856 day) 3.289)))
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1993-08-10 04:14:17 +00:00
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(mod (+ mean-anomaly
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(* 1.916 (solar-sin-degrees mean-anomaly))
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(* 0.020 (solar-sin-degrees (* 2 mean-anomaly)))
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282.634)
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360)))
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1992-08-12 12:49:57 +00:00
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(defun solar-right-ascension (longitude)
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"Right ascension of the sun, given its LONGITUDE."
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(solar-degrees-to-hours
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(solar-arctan
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(* solar-cos-inclination (solar-tangent-degrees longitude))
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(solar-degrees-to-quadrant longitude))))
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(defun solar-declination (longitude)
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"Declination of the sun, given its LONGITUDE."
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(solar-arcsin
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(* solar-sin-inclination
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(solar-sin-degrees longitude))))
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(defun solar-sunrise (date)
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"Calculates the *standard* time of sunrise for Gregorian DATE for location
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given by `calendar-latitude' and `calendar-longitude'. Returns a decimal fraction
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of hours. Returns nil if the sun does not rise at that location on that day."
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(let* ((day-of-year (calendar-day-number date))
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(approx-sunrise
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(+ day-of-year
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(solar-hours-to-days
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(- 6 (solar-degrees-to-hours calendar-longitude)))))
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(solar-longitude-of-sun-at-sunrise
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(solar-longitude-of-sun approx-sunrise))
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(solar-right-ascension-at-sunrise
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(solar-right-ascension solar-longitude-of-sun-at-sunrise))
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(solar-declination-at-sunrise
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(solar-declination solar-longitude-of-sun-at-sunrise))
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(cos-local-sunrise
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(/ (- (solar-cosine-degrees (+ 90 (/ 50.0 60.0)))
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(* (solar-sin-degrees solar-declination-at-sunrise)
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(solar-sin-degrees calendar-latitude)))
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(* (solar-cosine-degrees solar-declination-at-sunrise)
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(solar-cosine-degrees calendar-latitude)))))
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(if (<= (abs cos-local-sunrise) 1);; otherwise, no sunrise that day
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(let* ((local-sunrise (solar-degrees-to-hours
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(- 360 (solar-arccos cos-local-sunrise))))
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(local-mean-sunrise
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1993-08-10 04:14:17 +00:00
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(mod (- (+ local-sunrise solar-right-ascension-at-sunrise)
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(+ (* 0.065710 approx-sunrise)
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6.622))
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24)))
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1992-08-12 12:49:57 +00:00
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(+ (- local-mean-sunrise (solar-degrees-to-hours calendar-longitude))
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(/ calendar-time-zone 60.0))))))
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(defun solar-sunset (date)
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"Calculates the *standard* time of sunset for Gregorian DATE for location
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given by `calendar-latitude' and `calendar-longitude'. Returns a decimal fractions
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of hours. Returns nil if the sun does not set at that location on that day."
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(let* ((day-of-year (calendar-day-number date))
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(approx-sunset
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(+ day-of-year
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(solar-hours-to-days
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(- 18 (solar-degrees-to-hours calendar-longitude)))))
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(solar-longitude-of-sun-at-sunset
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(solar-longitude-of-sun approx-sunset))
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(solar-right-ascension-at-sunset
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(solar-right-ascension solar-longitude-of-sun-at-sunset))
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(solar-declination-at-sunset
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(solar-declination solar-longitude-of-sun-at-sunset))
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(cos-local-sunset
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(/ (- (solar-cosine-degrees (+ 90 (/ 50.0 60.0)))
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(* (solar-sin-degrees solar-declination-at-sunset)
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(solar-sin-degrees calendar-latitude)))
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(* (solar-cosine-degrees solar-declination-at-sunset)
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(solar-cosine-degrees calendar-latitude)))))
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(if (<= (abs cos-local-sunset) 1);; otherwise, no sunset that day
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(let* ((local-sunset (solar-degrees-to-hours
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(solar-arccos cos-local-sunset)))
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(local-mean-sunset
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1993-08-10 04:14:17 +00:00
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(mod (- (+ local-sunset solar-right-ascension-at-sunset)
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(+ (* 0.065710 approx-sunset) 6.622))
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24)))
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1992-08-12 12:49:57 +00:00
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(+ (- local-mean-sunset (solar-degrees-to-hours calendar-longitude))
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(/ calendar-time-zone 60.0))))))
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1993-06-16 23:12:21 +00:00
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(defun solar-time-string (time date &optional style)
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"Printable form for decimal fraction *standard* TIME on DATE.
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Optional parameter STYLE forces the time to be standard time when its value
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is 'standard and daylight savings time (if available) when its value is
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'daylight.
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1992-08-12 12:49:57 +00:00
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Format used is given by `calendar-time-display-form'. Converted to daylight
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1993-06-16 23:12:21 +00:00
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savings time according to `calendar-daylight-savings-starts',
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`calendar-daylight-savings-ends', `calendar-daylight-switchover-time', and
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`calendar-daylight-savings-offset'."
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1992-08-12 12:49:57 +00:00
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(let* ((year (extract-calendar-year date))
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1993-06-22 03:22:40 +00:00
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(time (round (* 60 time)))
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(rounded-abs-date (+ (calendar-absolute-from-gregorian date)
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(/ time 60.0 24.0)))
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1993-06-16 23:12:21 +00:00
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(dst-starts (and calendar-daylight-savings-starts
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(+ (calendar-absolute-from-gregorian
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(eval calendar-daylight-savings-starts))
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1993-06-22 03:22:40 +00:00
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(/ calendar-daylight-savings-switchover-time
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60.0 24.0))))
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1993-06-16 23:12:21 +00:00
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(dst-ends (and calendar-daylight-savings-ends
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(+ (calendar-absolute-from-gregorian
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(eval calendar-daylight-savings-ends))
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1993-06-22 03:22:40 +00:00
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(/ (- calendar-daylight-savings-switchover-time
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calendar-daylight-time-offset)
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60.0 24.0))))
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1993-06-16 23:12:21 +00:00
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(dst (and (not (eq style 'standard))
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(or (eq style 'daylight)
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(and dst-starts dst-ends
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(or (and (< dst-starts dst-ends);; northern hemi.
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(<= dst-starts rounded-abs-date)
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(< rounded-abs-date dst-ends))
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(and (< dst-ends dst-starts);; southern hemi.
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(or (< rounded-abs-date dst-ends)
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(<= dst-starts rounded-abs-date)))))
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(and dst-starts (not dst-ends)
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(<= dst-starts rounded-abs-date))
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(and dst-ends (not dst-starts)
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(< rounded-abs-date dst-ends)))))
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1992-08-12 12:49:57 +00:00
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(time-zone (if dst
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calendar-daylight-time-zone-name
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calendar-standard-time-zone-name))
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1993-06-22 03:22:40 +00:00
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(time (+ time (if dst calendar-daylight-time-offset 0)))
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(24-hours (/ time 60))
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(minutes (format "%02d" (% time 60)))
|
|
|
|
(12-hours (format "%d" (1+ (% (+ 24-hours 11) 12))))
|
1992-08-12 12:49:57 +00:00
|
|
|
(am-pm (if (>= 24-hours 12) "pm" "am"))
|
|
|
|
(24-hours (format "%02d" 24-hours)))
|
|
|
|
(mapconcat 'eval calendar-time-display-form "")))
|
|
|
|
|
|
|
|
(defun solar-sunrise-sunset (date)
|
|
|
|
"String giving local times of sunrise and sunset on Gregorian DATE."
|
|
|
|
(let ((rise (solar-sunrise date))
|
|
|
|
(set (solar-sunset date)))
|
|
|
|
(format "%s, %s at %s"
|
|
|
|
(if rise
|
|
|
|
(concat "Sunrise " (solar-time-string rise date))
|
|
|
|
"No sunrise")
|
|
|
|
(if set
|
|
|
|
(concat "sunset " (solar-time-string set date))
|
|
|
|
"no sunset")
|
|
|
|
(eval calendar-location-name))))
|
|
|
|
|
|
|
|
(defun solar-apparent-longitude-of-sun (date)
|
|
|
|
"Apparent longitude of the sun on Gregorian DATE."
|
|
|
|
(let* ((time (/ (- (calendar-absolute-from-gregorian date)
|
|
|
|
(calendar-absolute-from-gregorian '(1 0.5 1900)))
|
|
|
|
36525))
|
|
|
|
(l (+ 279.69668
|
|
|
|
(* 36000.76892 time)
|
|
|
|
(* 0.0003025 time time)))
|
|
|
|
(m (+ 358.47583
|
|
|
|
(* 35999.04975 time)
|
|
|
|
(* -0.000150 time time)
|
|
|
|
(* -0.0000033 time time time)))
|
|
|
|
(c (+ (* (+ 1.919460
|
|
|
|
(* -0.004789 time)
|
|
|
|
(* -0.000014 time time))
|
|
|
|
(solar-sin-degrees m))
|
|
|
|
(* (+ 0.020094
|
|
|
|
(* -0.000100 time))
|
|
|
|
(solar-sin-degrees (* 2 m)))
|
|
|
|
(* 0.000293
|
|
|
|
(solar-sin-degrees (* 3 m)))))
|
|
|
|
(L (+ l c))
|
|
|
|
(omega (+ 259.18
|
|
|
|
(* -1934.142 time)))
|
|
|
|
(app (+ L
|
|
|
|
-0.00569
|
|
|
|
(* -0.00479
|
|
|
|
(solar-sin-degrees omega)))))
|
|
|
|
app))
|
|
|
|
|
|
|
|
(defun solar-ephemeris-correction (year)
|
1993-06-16 23:12:21 +00:00
|
|
|
"Difference in minutes between Ephemeris time and UTC in YEAR.
|
1992-08-12 12:49:57 +00:00
|
|
|
Value is only an approximation."
|
|
|
|
(let ((T (/ (- year 1900) 100.0)))
|
|
|
|
(+ 0.41 (* 1.2053 T) (* 0.4992 T T))))
|
|
|
|
|
|
|
|
(defun solar-equinoxes/solstices (k year)
|
|
|
|
"Date of equinox/solstice K for YEAR. K=0, spring equinox; K=1, summer
|
|
|
|
solstice; K=2, fall equinox; K=3, winter solstice. Accurate to within
|
|
|
|
several minutes."
|
|
|
|
(let ((date (list (+ 3 (* k 3)) 21 year))
|
1993-06-22 03:22:40 +00:00
|
|
|
app
|
1992-08-12 12:49:57 +00:00
|
|
|
(correction 1000))
|
|
|
|
(while (> correction 0.00001)
|
1993-08-10 04:14:17 +00:00
|
|
|
(setq app (mod (solar-apparent-longitude-of-sun date) 360.0))
|
1992-08-12 12:49:57 +00:00
|
|
|
(setq correction (* 58 (solar-sin-degrees (- (* k 90) app))))
|
|
|
|
(setq date (list (extract-calendar-month date)
|
|
|
|
(+ (extract-calendar-day date) correction)
|
|
|
|
year)))
|
|
|
|
(list (extract-calendar-month date)
|
|
|
|
(+ (extract-calendar-day date) (/ calendar-time-zone 60.0 24.0)
|
|
|
|
(- (/ (solar-ephemeris-correction year) 60.0 24.0)))
|
|
|
|
year)))
|
|
|
|
|
|
|
|
;;;###autoload
|
|
|
|
(defun sunrise-sunset (&optional arg)
|
|
|
|
"Local time of sunrise and sunset for today. Accurate to +/- 2 minutes.
|
|
|
|
If called with an optional prefix argument, prompts for date.
|
|
|
|
|
|
|
|
If called with an optional double prefix argument, prompts for longitude,
|
|
|
|
latitude, time zone, and date.
|
|
|
|
|
|
|
|
This function is suitable for execution in a .emacs file."
|
|
|
|
(interactive "p")
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (and (< arg 16)
|
|
|
|
(not (and calendar-latitude calendar-longitude calendar-time-zone)))
|
|
|
|
(solar-setup))
|
1992-08-12 12:49:57 +00:00
|
|
|
(let* ((calendar-longitude
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (< arg 16) calendar-longitude
|
1992-08-12 12:49:57 +00:00
|
|
|
(solar-get-number
|
|
|
|
"Enter longitude (decimal fraction; + east, - west): ")))
|
|
|
|
(calendar-latitude
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (< arg 16) calendar-latitude
|
1992-08-12 12:49:57 +00:00
|
|
|
(solar-get-number
|
|
|
|
"Enter latitude (decimal fraction; + north, - south): ")))
|
|
|
|
(calendar-time-zone
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (< arg 16) calendar-time-zone
|
1992-08-12 12:49:57 +00:00
|
|
|
(solar-get-number
|
1993-06-16 23:12:21 +00:00
|
|
|
"Enter difference from Coordinated Universal Time (in minutes): ")))
|
1992-08-12 12:49:57 +00:00
|
|
|
(calendar-location-name
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (< arg 16) calendar-location-name
|
|
|
|
(let ((float-output-format "%.1f"))
|
|
|
|
(format "%s%s, %s%s"
|
|
|
|
(abs calendar-latitude)
|
|
|
|
(if (> calendar-latitude 0) "N" "S")
|
|
|
|
(abs calendar-longitude)
|
|
|
|
(if (> calendar-longitude 0) "E" "W")))))
|
1992-08-12 12:49:57 +00:00
|
|
|
(calendar-standard-time-zone-name
|
1992-08-19 03:54:46 +00:00
|
|
|
(if (< arg 16) calendar-standard-time-zone-name
|
1993-06-22 03:22:40 +00:00
|
|
|
(cond ((= calendar-time-zone 0) "UTC")
|
1992-08-19 03:54:46 +00:00
|
|
|
((< calendar-time-zone 0)
|
1993-06-22 03:22:40 +00:00
|
|
|
(format "UTC%dmin" calendar-time-zone))
|
|
|
|
(t (format "UTC+%dmin" calendar-time-zone)))))
|
1992-08-19 03:54:46 +00:00
|
|
|
(calendar-daylight-savings-starts
|
|
|
|
(if (< arg 16) calendar-daylight-savings-starts))
|
|
|
|
(calendar-daylight-savings-ends
|
|
|
|
(if (< arg 16) calendar-daylight-savings-ends))
|
|
|
|
(date (if (< arg 4) (calendar-current-date) (calendar-read-date)))
|
1992-08-12 12:49:57 +00:00
|
|
|
(date-string (calendar-date-string date t))
|
|
|
|
(time-string (solar-sunrise-sunset date))
|
|
|
|
(msg (format "%s: %s" date-string time-string))
|
|
|
|
(one-window (one-window-p t)))
|
|
|
|
(if (<= (length msg) (screen-width))
|
|
|
|
(message msg)
|
|
|
|
(with-output-to-temp-buffer "*temp*"
|
|
|
|
(princ (concat date-string "\n" time-string)))
|
|
|
|
(message (substitute-command-keys
|
|
|
|
(if one-window
|
|
|
|
(if pop-up-windows
|
|
|
|
"Type \\[delete-other-windows] to remove temp window."
|
|
|
|
"Type \\[switch-to-buffer] RET to remove temp window.")
|
|
|
|
"Type \\[switch-to-buffer-other-window] RET to restore old contents of temp window."))))))
|
|
|
|
|
|
|
|
(defun calendar-sunrise-sunset ()
|
|
|
|
"Local time of sunrise and sunset for date under cursor.
|
|
|
|
Accurate to +/- 2 minutes."
|
|
|
|
(interactive)
|
|
|
|
(if (not (and calendar-latitude calendar-longitude calendar-time-zone))
|
|
|
|
(solar-setup))
|
|
|
|
(message
|
|
|
|
(solar-sunrise-sunset
|
|
|
|
(or (calendar-cursor-to-date)
|
|
|
|
(error "Cursor is not on a date!")))))
|
|
|
|
|
|
|
|
(defun diary-sunrise-sunset ()
|
|
|
|
"Local time of sunrise and sunset as a diary entry.
|
|
|
|
Accurate to +/- 2 minutes."
|
|
|
|
(if (not (and calendar-latitude calendar-longitude calendar-time-zone))
|
|
|
|
(solar-setup))
|
|
|
|
(solar-sunrise-sunset date))
|
|
|
|
|
|
|
|
(defun diary-sabbath-candles ()
|
|
|
|
"Local time of candle lighting diary entry--applies if date is a Friday.
|
|
|
|
No diary entry if there is no sunset on that date."
|
|
|
|
(if (not (and calendar-latitude calendar-longitude calendar-time-zone))
|
|
|
|
(solar-setup))
|
|
|
|
(if (= (% (calendar-absolute-from-gregorian date) 7) 5);; Friday
|
|
|
|
(let* ((sunset (solar-sunset date))
|
|
|
|
(light (if sunset (- sunset (/ 18.0 60.0)))))
|
|
|
|
(if light (format "%s Sabbath candle lighting"
|
|
|
|
(solar-time-string light date))))))
|
|
|
|
|
1993-06-22 03:22:40 +00:00
|
|
|
(defun solar-equinoxes-solstices ()
|
1992-08-12 12:49:57 +00:00
|
|
|
"Date and time of equinoxes and solstices, if visible in the calendar window.
|
|
|
|
Requires floating point."
|
1993-06-22 03:22:40 +00:00
|
|
|
(let ((m displayed-month)
|
|
|
|
(y displayed-year))
|
1992-08-12 12:49:57 +00:00
|
|
|
(increment-calendar-month m y (cond ((= 1 (% m 3)) -1)
|
|
|
|
((= 2 (% m 3)) 1)
|
|
|
|
(t 0)))
|
|
|
|
(let* ((calendar-standard-time-zone-name
|
1993-06-22 03:22:40 +00:00
|
|
|
(if calendar-time-zone calendar-standard-time-zone-name "UTC"))
|
1992-08-12 12:49:57 +00:00
|
|
|
(calendar-daylight-savings-starts
|
|
|
|
(if calendar-time-zone calendar-daylight-savings-starts))
|
|
|
|
(calendar-daylight-savings-ends
|
|
|
|
(if calendar-time-zone calendar-daylight-savings-ends))
|
|
|
|
(calendar-time-zone (if calendar-time-zone calendar-time-zone 0))
|
|
|
|
(k (1- (/ m 3)))
|
|
|
|
(date (solar-equinoxes/solstices k y))
|
|
|
|
(day (extract-calendar-day date))
|
|
|
|
(time (* 24 (- day (truncate day))))
|
|
|
|
;; Time zone/DST can't move the date out of range,
|
|
|
|
;; so let solar-time-string do the conversion.
|
|
|
|
(date (list (extract-calendar-month date)
|
|
|
|
(truncate day)
|
|
|
|
(extract-calendar-year date))))
|
|
|
|
(list (list date
|
|
|
|
(format "%s %s"
|
|
|
|
(cond ((= k 0) "Vernal Equinox")
|
|
|
|
((= k 1) "Summer Solstice")
|
|
|
|
((= k 2) "Fall Equinox")
|
|
|
|
((= k 3) "Winter Solstice"))
|
|
|
|
(solar-time-string time date)))))))
|
|
|
|
|
|
|
|
(provide 'solar)
|
|
|
|
|
|
|
|
;;; solar.el ends here
|