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633 lines
25 KiB
EmacsLisp
633 lines
25 KiB
EmacsLisp
;;; solar.el --- calendar functions for solar events.
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;; Copyright (C) 1992, 1993, 1995 Free Software Foundation, Inc.
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;; Author: Edward M. Reingold <reingold@cs.uiuc.edu>
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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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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software; you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 2, or (at your option)
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;; any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs; see the file COPYING. If not, write to
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;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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;;; Commentary:
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;; This collection of functions implements the features of calendar.el,
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;; diary.el, and holiday.el that deal with times of day, sunrise/sunset, and
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;; eqinoxes/solstices.
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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, on
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;; ``Astronomical Formulae for Calculators,'' 3rd ed., by Jean Meeus,
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;; Willmann-Bell, Inc., 1985, and on ``Astronomical Algorithms'' by Jean
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;; Meeus, Willmann-Bell, Inc., 1991.
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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/lunar calculations impossible since floating point is unavailable."))
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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.
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The value can be either a decimal fraction (one place of accuracy is
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sufficient), + north, - south, such as 40.7 for New York City, or the value
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can be a vector [degrees minutes north/south] such as [40 50 north] for New
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York City.
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This variable should be set in site-local.el.")
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;;;###autoload
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(defvar calendar-longitude nil
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"*Longitude of `calendar-location-name' in degrees.
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The value can be either a decimal fraction (one place of accuracy is
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sufficient), + east, - west, such as -73.9 for New York City, or the value
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can be a vector [degrees minutes east/west] such as [73 55 west] for New
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York City.
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This variable should be set in site-local.el.")
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(defsubst calendar-latitude ()
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"Convert calendar-latitude to a signed decimal fraction, if needed."
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(if (numberp calendar-latitude)
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calendar-latitude
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(let ((lat (+ (aref calendar-latitude 0)
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(/ (aref calendar-latitude 1) 60.0))))
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(if (equal (aref calendar-latitude 2) 'north)
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lat
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(- lat)))))
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(defsubst calendar-longitude ()
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"Convert calendar-longitude to a signed decimal fraction, if needed."
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(if (numberp calendar-longitude)
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calendar-longitude
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(let ((long (+ (aref calendar-longitude 0)
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(/ (aref calendar-longitude 1) 60.0))))
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(if (equal (aref calendar-longitude 2) 'east)
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long
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(- long)))))
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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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(if (numberp calendar-latitude)
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(abs calendar-latitude)
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(+ (aref calendar-latitude 0)
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(/ (aref calendar-latitude 1) 60.0)))
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(if (numberp calendar-latitude)
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(if (> calendar-latitude 0) "N" "S")
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(if (equal (aref calendar-latitude 2) 'north) "N" "S"))
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(if (numberp calendar-longitude)
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(abs calendar-longitude)
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(+ (aref calendar-longitude 0)
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(/ (aref calendar-longitude 1) 60.0)))
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(if (numberp calendar-longitude)
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(if (> calendar-longitude 0) "E" "W")
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(if (equal (aref calendar-longitude 2) 'east) "E" "W"))))
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"*Expression evaluating to name of `calendar-longitude', calendar-latitude'.
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For example, \"New York City\". Default value is just the latitude, longitude
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pair.
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This variable should be set in site-local.el.")
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(defvar solar-n-hemi-seasons
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'("Vernal Equinox" "Summer Solstice" "Autumnal Equinox" "Winter Solstice")
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"List of season changes for the northern hemisphere.")
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(defvar solar-s-hemi-seasons
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'("Autumnal Equinox" "Winter Solstice" "Vernal Equinox" "Summer Solstice")
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"List of season changes for the southern hemisphere.")
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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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"Enter difference from Coordinated Universal Time (in minutes): "))))
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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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(defsubst solar-sin-degrees (x)
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(sin (degrees-to-radians (mod x 360.0))))
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(defsubst solar-cosine-degrees (x)
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(cos (degrees-to-radians (mod x 360.0))))
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(defsubst solar-tangent-degrees (x)
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(tan (degrees-to-radians (mod x 360.0))))
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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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(1+ (floor (mod angle 360) 90)))
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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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(defsubst solar-degrees-to-hours (deg)
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(/ deg 15.0))
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(defsubst solar-hours-to-days (hour)
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(/ hour 24.0))
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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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(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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(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.
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Calculation is for location given by `calendar-latitude' and
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`calendar-longitude'.
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Returns a decimal fraction of hours. Returns nil if the sun does not rise at
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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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(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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(+ (- 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.
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Calculation is for location given by `calendar-latitude' and
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`calendar-longitude'.
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Returns a decimal fractions of hours. Returns nil if the sun does not set at
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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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(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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(+ (- local-mean-sunset (solar-degrees-to-hours (calendar-longitude)))
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(/ calendar-time-zone 60.0))))))
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(defun solar-time-string (time time-zone)
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"Printable form for decimal fraction TIME in TIME-ZONE.
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Format used is given by `calendar-time-display-form'."
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(let* ((time (round (* 60 time)))
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(24-hours (/ time 60))
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(minutes (format "%02d" (% time 60)))
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(12-hours (format "%d" (1+ (% (+ 24-hours 11) 12))))
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(am-pm (if (>= 24-hours 12) "pm" "am"))
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(24-hours (format "%02d" 24-hours)))
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(mapconcat 'eval calendar-time-display-form "")))
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(defun solar-sunrise-sunset (date)
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"String giving local times of sunrise and sunset on Gregorian DATE."
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(let* ((rise (solar-sunrise date))
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(adj-rise (if rise (dst-adjust-time date rise)))
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(set (solar-sunset date))
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(adj-set (if set (dst-adjust-time date set))))
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(format "%s, %s at %s"
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(if (and rise (calendar-date-equal date (car adj-rise)))
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(concat "Sunrise " (apply 'solar-time-string (cdr adj-rise)))
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"No sunrise")
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(if (and set (calendar-date-equal date (car adj-set)))
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(concat "sunset " (apply 'solar-time-string (cdr adj-set)))
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"no sunset")
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(eval calendar-location-name))))
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(defun solar-date-next-longitude (d l)
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"First moment on or after Julian day number D when sun's longitude is a
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multiple of L degrees at calendar-location-name with that location's
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local time (including any daylight savings rules).
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L must be an integer divisor of 360.
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Result is in local time expressed astronomical (Julian) day numbers.
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The values of calendar-daylight-savings-starts,
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calendar-daylight-savings-starts-time, calendar-daylight-savings-ends,
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calendar-daylight-savings-ends-time, calendar-daylight-time-offset, and
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calendar-time-zone are used to interpret local time."
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(let* ((long)
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(start d)
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(start-long (solar-longitude d))
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(next (mod (* l (1+ (floor (/ start-long l)))) 360))
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(end (+ d (* (/ l 360.0) 400)))
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(end-long (solar-longitude end)))
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(while ;; bisection search for nearest minute
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(< 0.00001 (- end start))
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;; start <= d < end
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;; start-long <= next < end-long when next != 0
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;; when next = 0, we look for the discontinuity (start-long is near 360
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;; and end-long is small (less than l).
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(setq d (/ (+ start end) 2.0))
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(setq long (solar-longitude d))
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(if (or (and (/= next 0) (< long next))
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(and (= next 0) (< l long)))
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(progn
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(setq start d)
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(setq start-long long))
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(setq end d)
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(setq end-long long)))
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(/ (+ start end) 2.0)))
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(defun solar-longitude (d)
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"Longitude of sun on astronomical (Julian) day number D.
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Accurary is about 0.01 degree (about 365.25*24*60*0.01/360 = 15 minutes).
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The values of calendar-daylight-savings-starts,
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calendar-daylight-savings-starts-time, calendar-daylight-savings-ends,
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calendar-daylight-savings-ends-time, calendar-daylight-time-offset, and
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calendar-time-zone are used to interpret local time."
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(let* ((a-d (calendar-absolute-from-astro d))
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(date (calendar-gregorian-from-absolute (floor a-d)))
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(time (* 24 (- a-d (truncate a-d))))
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(rounded-abs-date (+ (calendar-absolute-from-gregorian date)
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(/ (round (* 60 time)) 60.0 24.0)))
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;; get local standard time
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(a-d (- rounded-abs-date
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(if (dst-in-effect rounded-abs-date)
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(/ calendar-daylight-time-offset 24.0 60.0) 0)))
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;; get Universal Time
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(a-d (- a-d (/ calendar-time-zone 60.0 24.0)))
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(date (calendar-astro-from-absolute a-d))
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;; get Ephemeris Time
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(date (+ date (solar-ephemeris-correction
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(extract-calendar-year
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(calendar-gregorian-from-absolute
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(floor
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(calendar-absolute-from-astro
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date)))))))
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(T (/ (- date 2451545.0) 36525.0))
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(Lo (mod (+ 280.46645 (* 36000.76983 T) (* 0.0003032 T T)) 360.0))
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(M (mod (+ 357.52910
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(* 35999.05030 T)
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(* -0.0001559 T T)
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(* -0.00000048 T T T))
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360.0))
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(e (+ 0.016708617 (* -0.000042037 T) (* -0.0000001236 T T)))
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(C (+ (* (+ 1.914600 (* -0.004817 T) (* -0.000014 T T))
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(solar-sin-degrees M))
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(* (+ 0.019993 (* -0.000101 T)) (solar-sin-degrees (* 2 M)))
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(* 0.000290 (solar-sin-degrees (* 3 M)))))
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(true-longitude (+ Lo C))
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(omega (+ 125.04 (* -1934.136 T)))
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(apparent-longitude (mod
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(+ true-longitude
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-0.00569
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(* -0.00478 (solar-sin-degrees omega)))
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360.0)))
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apparent-longitude))
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(defun solar-ephemeris-correction (year)
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"Ephemeris time minus Universal Time at astronomical (Julian) day D.
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Result is in days For the years 1800-1987, the maximum error is 1.9 seconds.
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For the other years, the maximum error is about 30 seconds."
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(cond ((and (<= 1988 year) (< year 2020))
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(/ (+ year -2000 67.0) 60.0 60.0 24.0))
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|
((and (<= 1900 year) (< year 1988))
|
|
(let* ((theta (/ (- (calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
(list 7 1 year)))
|
|
(calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
'(1 1 1900))))
|
|
36525.0))
|
|
(theta2 (* theta theta))
|
|
(theta3 (* theta2 theta))
|
|
(theta4 (* theta2 theta2))
|
|
(theta5 (* theta3 theta2)))
|
|
(+ -0.00002
|
|
(* 0.000297 theta)
|
|
(* 0.025184 theta2)
|
|
(* -0.181133 theta3)
|
|
(* 0.553040 theta4)
|
|
(* -0.861938 theta5)
|
|
(* 0.677066 theta3 theta3)
|
|
(* -0.212591 theta4 theta3))))
|
|
((and (<= 1800 year) (< year 1900))
|
|
(let* ((theta (/ (- (calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
(list 7 1 year)))
|
|
(calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
'(1 1 1900))))
|
|
36525.0))
|
|
(theta2 (* theta theta))
|
|
(theta3 (* theta2 theta))
|
|
(theta4 (* theta2 theta2))
|
|
(theta5 (* theta3 theta2)))
|
|
(+ -0.000009
|
|
(* 0.003844 theta)
|
|
(* 0.083563 theta2)
|
|
(* 0.865736 theta3)
|
|
(* 4.867575 theta4)
|
|
(* 15.845535 theta5)
|
|
(* 31.332267 theta3 theta3)
|
|
(* 38.291999 theta4 theta3)
|
|
(* 28.316289 theta4 theta4)
|
|
(* 11.636204 theta4 theta5)
|
|
(* 2.043794 theta5 theta5))))
|
|
((and (<= 1620 year) (< year 1800))
|
|
(let ((x (/ (- year 1600) 10.0)))
|
|
(/ (+ (* 2.19167 x x) (* -40.675 x) 196.58333) 60.0 60.0 24.0)))
|
|
(t (let* ((tmp (- (calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
(list 1 1 year)))
|
|
2382148))
|
|
(second (- (/ (* tmp tmp) 41048480.0) 15)))
|
|
(/ second 60.0 60.0 24.0)))))
|
|
|
|
;;;###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, prompt for date.
|
|
|
|
If called with an optional double prefix argument, prompt for longitude,
|
|
latitude, time zone, and date, and always use standard time.
|
|
|
|
This function is suitable for execution in a .emacs file."
|
|
(interactive "p")
|
|
(or arg (setq arg 1))
|
|
(if (and (< arg 16)
|
|
(not (and calendar-latitude calendar-longitude calendar-time-zone)))
|
|
(solar-setup))
|
|
(let* ((calendar-longitude
|
|
(if (< arg 16) calendar-longitude
|
|
(solar-get-number
|
|
"Enter longitude (decimal fraction; + east, - west): ")))
|
|
(calendar-latitude
|
|
(if (< arg 16) calendar-latitude
|
|
(solar-get-number
|
|
"Enter latitude (decimal fraction; + north, - south): ")))
|
|
(calendar-time-zone
|
|
(if (< arg 16) calendar-time-zone
|
|
(solar-get-number
|
|
"Enter difference from Coordinated Universal Time (in minutes): ")))
|
|
(calendar-location-name
|
|
(if (< arg 16) calendar-location-name
|
|
(let ((float-output-format "%.1f"))
|
|
(format "%s%s, %s%s"
|
|
(if (numberp calendar-latitude)
|
|
(abs calendar-latitude)
|
|
(+ (aref calendar-latitude 0)
|
|
(/ (aref calendar-latitude 1) 60.0)))
|
|
(if (numberp calendar-latitude)
|
|
(if (> calendar-latitude 0) "N" "S")
|
|
(if (equal (aref calendar-latitude 2) 'north) "N" "S"))
|
|
(if (numberp calendar-longitude)
|
|
(abs calendar-longitude)
|
|
(+ (aref calendar-longitude 0)
|
|
(/ (aref calendar-longitude 1) 60.0)))
|
|
(if (numberp calendar-longitude)
|
|
(if (> calendar-longitude 0) "E" "W")
|
|
(if (equal (aref calendar-longitude 2) 'east)
|
|
"E" "W"))))))
|
|
(calendar-standard-time-zone-name
|
|
(if (< arg 16) calendar-standard-time-zone-name
|
|
(cond ((= calendar-time-zone 0) "UTC")
|
|
((< calendar-time-zone 0)
|
|
(format "UTC%dmin" calendar-time-zone))
|
|
(t (format "UTC+%dmin" calendar-time-zone)))))
|
|
(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)))
|
|
(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) (frame-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))
|
|
(let ((date (calendar-cursor-to-date t)))
|
|
(message "%s: %s"
|
|
(calendar-date-string date t t)
|
|
(solar-sunrise-sunset 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
|
|
(dst-adjust-time
|
|
date
|
|
(- sunset (/ 18.0 60.0))))))
|
|
(if (and light (calendar-date-equal date (car light)))
|
|
(format "%s Sabbath candle lighting"
|
|
(apply 'solar-time-string (cdr light)))))))
|
|
|
|
;;;###autoload
|
|
(defun solar-equinoxes-solstices ()
|
|
"Date and time of equinoxes and solstices, if visible in the calendar window.
|
|
Requires floating point."
|
|
(let ((m displayed-month)
|
|
(y displayed-year))
|
|
(increment-calendar-month m y (cond ((= 1 (% m 3)) -1)
|
|
((= 2 (% m 3)) 1)
|
|
(t 0)))
|
|
(let* ((calendar-standard-time-zone-name
|
|
(if calendar-time-zone calendar-standard-time-zone-name "UTC"))
|
|
(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)))
|
|
(d (solar-date-next-longitude
|
|
(calendar-astro-from-absolute
|
|
(calendar-absolute-from-gregorian
|
|
(list (+ 3 (* k 3)) 15 y)))
|
|
90))
|
|
(abs-day (calendar-absolute-from-astro d)))
|
|
(list
|
|
(list (calendar-gregorian-from-absolute (floor abs-day))
|
|
(format "%s %s"
|
|
(nth k (if (and calendar-latitude
|
|
(< (calendar-latitude) 0))
|
|
solar-s-hemi-seasons
|
|
solar-n-hemi-seasons))
|
|
(solar-time-string
|
|
(* 24 (- abs-day (floor abs-day)))
|
|
(if (dst-in-effect abs-day)
|
|
calendar-daylight-time-zone-name
|
|
calendar-standard-time-zone-name))))))))
|
|
|
|
|
|
(provide 'solar)
|
|
|
|
;;; solar.el ends here
|