BangleApps/apps/rebble/suncalc.js

/*
 (c) 2011-2015, Vladimir Agafonkin
 SunCalc is a JavaScript library for calculating sun/moon position and light phases.
 https://github.com/mourner/suncalc
 
 edit for banglejs
*/

(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 declination(l, b)    { return asin(sin(b) * cos(e) + cos(b) * sin(e) * sin(l)); }


// 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;
}

var SunCalc = {};


// 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'  ]
];



// 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;
};


// 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;


}());