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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.
https://github.com/mourner/suncalc
*/
(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; }
// 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) {
var arg = (sin(h) - sin(phi) * sin(d)) / (cos(phi) * cos(d));
if(arg > 1) return -Infinity;
if(arg < -1) return Infinity;
return acos(arg);
}
// returns set time for the given sun altitude
function getSetJ(h, lw, phi, dec, n, M, L) {
var w = hourAngle(h, phi, dec);
if(!isFinite(w))
return w;
var a = approxTransit(w, lw, n);
return solarTransitJ(a, M, L);
}
// calculates sun times for a given date and latitude/longitude
SunCalc.getTimes = function (date, lat, lng) {
// https://github.com/mourner/suncalc/issues/11#issuecomment-34809666
date = new Date(date.getFullYear(), date.getMonth(), date.getDate(), 12);
var lw = rad * -lng,
phi = rad * lat,
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, 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];
Jset = getSetJ(time[0] * rad, lw, phi, dec, n, M, L);
if(!isFinite(Jset))
Jnoon = 0;
Jrise = Jnoon - (Jset - Jnoon);
result[time[1]] = fromJulianConstrained(date, Jrise);
result[time[2]] = fromJulianConstrained(date, Jset);
}
return result;
};
function fromJulianConstrained(date, j) {
var result,
min,
max;
min = new Date(date.getTime());
min.setHours(0, 0, 0, 0);
max = new Date(min.getTime() + dayMs);
if(!isFinite(j))
return j < 0 ? min : max;
result = fromJulian(j);
if(result < min)
return min;
if(result > max)
return max;
return result;
}
// export as AMD module / Node module / browser variable
if (typeof define === 'function' && define.amd) define(SunCalc);
else if (typeof module !== 'undefined') module.exports = SunCalc;
else window.SunCalc = SunCalc;
}());