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suncalc.js
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suncalc.js
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/*
(c) 2011-2015, Vladimir Agafonkin
SunCalc is a JavaScript library for calculating sun/moon position and light phases.
Copied at commit 031c4ad3f6f330a02863ec0f43b820115294ccca from Dec 27, 2019 from https://github.com/mourner/suncalc
Copyright (c) 2014, Vladimir Agafonkin
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are
permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright notice, this list of
conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list
of conditions and the following disclaimer in the documentation and/or other materials
provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
(function () { 'use strict';
// shortcuts for easier to read formulas
var PI = Math.PI,
sin = Math.sin,
cos = Math.cos,
tan = Math.tan,
asin = Math.asin,
atan = Math.atan2,
acos = Math.acos,
rad = PI / 180;
// sun calculations are based on http://aa.quae.nl/en/reken/zonpositie.html formulas
// date/time constants and conversions
var dayMs = 1000 * 60 * 60 * 24,
J1970 = 2440588,
J2000 = 2451545;
function toJulian(date) { return date.valueOf() / dayMs - 0.5 + J1970; }
function fromJulian(j) { return new Date((j + 0.5 - J1970) * dayMs); }
function toDays(date) { return toJulian(date) - J2000; }
// general calculations for position
var e = rad * 23.4397; // obliquity of the Earth
function rightAscension(l, b) { return atan(sin(l) * cos(e) - tan(b) * sin(e), cos(l)); }
function declination(l, b) { return asin(sin(b) * cos(e) + cos(b) * sin(e) * sin(l)); }
function azimuth(H, phi, dec) { return atan(sin(H), cos(H) * sin(phi) - tan(dec) * cos(phi)); }
function altitude(H, phi, dec) { return asin(sin(phi) * sin(dec) + cos(phi) * cos(dec) * cos(H)); }
function siderealTime(d, lw) { return rad * (280.16 + 360.9856235 * d) - lw; }
function astroRefraction(h) {
if (h < 0) // the following formula works for positive altitudes only.
h = 0; // if h = -0.08901179 a div/0 would occur.
// formula 16.4 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
// 1.02 / tan(h + 10.26 / (h + 5.10)) h in degrees, result in arc minutes -> converted to rad:
return 0.0002967 / Math.tan(h + 0.00312536 / (h + 0.08901179));
}
// general sun calculations
function solarMeanAnomaly(d) { return rad * (357.5291 + 0.98560028 * d); }
function eclipticLongitude(M) {
var C = rad * (1.9148 * sin(M) + 0.02 * sin(2 * M) + 0.0003 * sin(3 * M)), // equation of center
P = rad * 102.9372; // perihelion of the Earth
return M + C + P + PI;
}
function sunCoords(d) {
var M = solarMeanAnomaly(d),
L = eclipticLongitude(M);
return {
dec: declination(L, 0),
ra: rightAscension(L, 0)
};
}
var SunCalc = {};
// calculates sun position for a given date and latitude/longitude
SunCalc.getPosition = function (date, lat, lng) {
var lw = rad * -lng,
phi = rad * lat,
d = toDays(date),
c = sunCoords(d),
H = siderealTime(d, lw) - c.ra;
return {
azimuth: azimuth(H, phi, c.dec),
altitude: altitude(H, phi, c.dec)
};
};
// sun times configuration (angle, morning name, evening name)
var times = SunCalc.times = [
[-0.833, 'sunrise', 'sunset' ],
[ -0.3, 'sunriseEnd', 'sunsetStart' ],
[ -6, 'dawn', 'dusk' ],
[ -12, 'nauticalDawn', 'nauticalDusk'],
[ -18, 'nightEnd', 'night' ],
[ 6, 'goldenHourEnd', 'goldenHour' ]
];
// adds a custom time to the times config
SunCalc.addTime = function (angle, riseName, setName) {
times.push([angle, riseName, setName]);
};
// calculations for sun times
var J0 = 0.0009;
function julianCycle(d, lw) { return Math.round(d - J0 - lw / (2 * PI)); }
function approxTransit(Ht, lw, n) { return J0 + (Ht + lw) / (2 * PI) + n; }
function solarTransitJ(ds, M, L) { return J2000 + ds + 0.0053 * sin(M) - 0.0069 * sin(2 * L); }
function hourAngle(h, phi, d) { return acos((sin(h) - sin(phi) * sin(d)) / (cos(phi) * cos(d))); }
function observerAngle(height) { return -2.076 * Math.sqrt(height) / 60; }
// returns set time for the given sun altitude
function getSetJ(h, lw, phi, dec, n, M, L) {
var w = hourAngle(h, phi, dec),
a = approxTransit(w, lw, n);
return solarTransitJ(a, M, L);
}
// calculates sun times for a given date, latitude/longitude, and, optionally,
// the observer height (in meters) relative to the horizon
SunCalc.getTimes = function (date, lat, lng, height) {
height = height || 0;
var lw = rad * -lng,
phi = rad * lat,
dh = observerAngle(height),
d = toDays(date),
n = julianCycle(d, lw),
ds = approxTransit(0, lw, n),
M = solarMeanAnomaly(ds),
L = eclipticLongitude(M),
dec = declination(L, 0),
Jnoon = solarTransitJ(ds, M, L),
i, len, time, h0, Jset, Jrise;
var result = {
solarNoon: fromJulian(Jnoon),
nadir: fromJulian(Jnoon - 0.5)
};
for (i = 0, len = times.length; i < len; i += 1) {
time = times[i];
h0 = (time[0] + dh) * rad;
Jset = getSetJ(h0, lw, phi, dec, n, M, L);
Jrise = Jnoon - (Jset - Jnoon);
result[time[1]] = fromJulian(Jrise);
result[time[2]] = fromJulian(Jset);
}
return result;
};
// moon calculations, based on http://aa.quae.nl/en/reken/hemelpositie.html formulas
function moonCoords(d) { // geocentric ecliptic coordinates of the moon
var L = rad * (218.316 + 13.176396 * d), // ecliptic longitude
M = rad * (134.963 + 13.064993 * d), // mean anomaly
F = rad * (93.272 + 13.229350 * d), // mean distance
l = L + rad * 6.289 * sin(M), // longitude
b = rad * 5.128 * sin(F), // latitude
dt = 385001 - 20905 * cos(M); // distance to the moon in km
return {
ra: rightAscension(l, b),
dec: declination(l, b),
dist: dt
};
}
SunCalc.getMoonPosition = function (date, lat, lng) {
var lw = rad * -lng,
phi = rad * lat,
d = toDays(date),
c = moonCoords(d),
H = siderealTime(d, lw) - c.ra,
h = altitude(H, phi, c.dec),
// formula 14.1 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
pa = atan(sin(H), tan(phi) * cos(c.dec) - sin(c.dec) * cos(H));
h = h + astroRefraction(h); // altitude correction for refraction
return {
azimuth: azimuth(H, phi, c.dec),
altitude: h,
distance: c.dist,
parallacticAngle: pa
};
};
// calculations for illumination parameters of the moon,
// based on http://idlastro.gsfc.nasa.gov/ftp/pro/astro/mphase.pro formulas and
// Chapter 48 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
SunCalc.getMoonIllumination = function (date) {
var d = toDays(date || new Date()),
s = sunCoords(d),
m = moonCoords(d),
sdist = 149598000, // distance from Earth to Sun in km
phi = acos(sin(s.dec) * sin(m.dec) + cos(s.dec) * cos(m.dec) * cos(s.ra - m.ra)),
inc = atan(sdist * sin(phi), m.dist - sdist * cos(phi)),
angle = atan(cos(s.dec) * sin(s.ra - m.ra), sin(s.dec) * cos(m.dec) -
cos(s.dec) * sin(m.dec) * cos(s.ra - m.ra));
return {
fraction: (1 + cos(inc)) / 2,
phase: 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / Math.PI,
angle: angle
};
};
function hoursLater(date, h) {
return new Date(date.valueOf() + h * dayMs / 24);
}
// calculations for moon rise/set times are based on http://www.stargazing.net/kepler/moonrise.html article
SunCalc.getMoonTimes = function (date, lat, lng, inUTC) {
var t = new Date(date);
if (inUTC) t.setUTCHours(0, 0, 0, 0);
else t.setHours(0, 0, 0, 0);
var hc = 0.133 * rad,
h0 = SunCalc.getMoonPosition(t, lat, lng).altitude - hc,
h1, h2, rise, set, a, b, xe, ye, d, roots, x1, x2, dx;
// go in 2-hour chunks, each time seeing if a 3-point quadratic curve crosses zero (which means rise or set)
for (var i = 1; i <= 24; i += 2) {
h1 = SunCalc.getMoonPosition(hoursLater(t, i), lat, lng).altitude - hc;
h2 = SunCalc.getMoonPosition(hoursLater(t, i + 1), lat, lng).altitude - hc;
a = (h0 + h2) / 2 - h1;
b = (h2 - h0) / 2;
xe = -b / (2 * a);
ye = (a * xe + b) * xe + h1;
d = b * b - 4 * a * h1;
roots = 0;
if (d >= 0) {
dx = Math.sqrt(d) / (Math.abs(a) * 2);
x1 = xe - dx;
x2 = xe + dx;
if (Math.abs(x1) <= 1) roots++;
if (Math.abs(x2) <= 1) roots++;
if (x1 < -1) x1 = x2;
}
if (roots === 1) {
if (h0 < 0) rise = i + x1;
else set = i + x1;
} else if (roots === 2) {
rise = i + (ye < 0 ? x2 : x1);
set = i + (ye < 0 ? x1 : x2);
}
if (rise && set) break;
h0 = h2;
}
var result = {};
if (rise) result.rise = hoursLater(t, rise);
if (set) result.set = hoursLater(t, set);
if (!rise && !set) result[ye > 0 ? 'alwaysUp' : 'alwaysDown'] = true;
return result;
};
// export as Node module / AMD module / browser variable
if (typeof exports === 'object' && typeof module !== 'undefined') module.exports = SunCalc;
else if (typeof define === 'function' && define.amd) define(SunCalc);
else window.SunCalc = SunCalc;
}());