87 lines
2.1 KiB
JavaScript
87 lines
2.1 KiB
JavaScript
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/*
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(c) 2011-2014, Vladimir Agafonkin
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SunCalc is a JavaScript library for calculating sun/mooon position and light phases.
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https://github.com/mourner/suncalc
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*/
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// shortcuts for easier to read formulas
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var PI = Math.PI,
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sin = Math.sin,
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cos = Math.cos,
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tan = Math.tan,
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asin = Math.asin,
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atan = Math.atan2,
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rad = PI / 180; // sun calculations are based on http://aa.quae.nl/en/reken/zonpositie.html formulas
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// date/time constants and conversions
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var dayMs = 1000 * 60 * 60 * 24,
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J1970 = 2440588,
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J2000 = 2451545;
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function toJulian(date) {
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return date.valueOf() / dayMs - 0.5 + J1970;
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}
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function toDays(date) {
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return toJulian(date) - J2000;
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} // general calculations for position
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var e = rad * 23.4397; // obliquity of the Earth
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function rightAscension(l, b) {
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return atan(sin(l) * cos(e) - tan(b) * sin(e), cos(l));
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}
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function declination(l, b) {
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return asin(sin(b) * cos(e) + cos(b) * sin(e) * sin(l));
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}
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function azimuth(H, phi, dec) {
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return atan(sin(H), cos(H) * sin(phi) - tan(dec) * cos(phi));
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}
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function altitude(H, phi, dec) {
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return asin(sin(phi) * sin(dec) + cos(phi) * cos(dec) * cos(H));
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}
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function siderealTime(d, lw) {
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return rad * (280.16 + 360.9856235 * d) - lw;
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} // general sun calculations
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function solarMeanAnomaly(d) {
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return rad * (357.5291 + 0.98560028 * d);
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}
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function eclipticLongitude(M) {
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var C = rad * (1.9148 * sin(M) + 0.02 * sin(2 * M) + 0.0003 * sin(3 * M)),
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// equation of center
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P = rad * 102.9372; // perihelion of the Earth
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return M + C + P + PI;
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}
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function sunCoords(d) {
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var M = solarMeanAnomaly(d),
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L = eclipticLongitude(M);
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return {
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dec: declination(L, 0),
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ra: rightAscension(L, 0)
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};
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}
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var SunCalc = {}; // calculates sun position for a given date and latitude/longitude
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SunCalc.getPosition = function (date, lat, lng) {
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var lw = rad * -lng,
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phi = rad * lat,
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d = toDays(date),
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c = sunCoords(d),
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H = siderealTime(d, lw) - c.ra;
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return {
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azimuth: azimuth(H, phi, c.dec),
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altitude: altitude(H, phi, c.dec)
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};
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};
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export default SunCalc;
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