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toDays, moonCoords and sunCoords now public from SunCalc #30

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toDays, moonCoords and sunCoords now public from SunCalc #30

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7cb4a40
add SunCalc.getMoonTimes, close #7
mourner May 16, 2014
bf35777
add alwaysUp/alwaysDown to getMoonTimes results
mourner May 16, 2014
ee593f7
toDays, moonCoords and sunCoords now public from SunCalc
clicktrend Jul 18, 2014
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90 changes: 76 additions & 14 deletions suncalc.js
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,11 @@ var dayMs = 1000 * 60 * 60 * 24,
J1970 = 2440588,
J2000 = 2451545;

var SunCalc = {};

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; }
SunCalc.toDays = function (date) { return toJulian(date) - J2000; }


// general calculations for position
Expand Down Expand Up @@ -56,7 +58,7 @@ function eclipticLongitude(M) {
return M + C + P + PI;
}

function sunCoords(d) {
SunCalc.sunCoords = function (d) {

var M = solarMeanAnomaly(d),
L = eclipticLongitude(M);
Expand All @@ -68,18 +70,15 @@ function sunCoords(d) {
}


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),
d = SunCalc.toDays(date),

c = sunCoords(d),
c = SunCalc.sunCoords(d),
H = siderealTime(d, lw) - c.ra;

return {
Expand Down Expand Up @@ -134,7 +133,7 @@ SunCalc.getTimes = function (date, lat, lng) {
var lw = rad * -lng,
phi = rad * lat,

d = toDays(date),
d = SunCalc.toDays(date),
n = julianCycle(d, lw),
ds = approxTransit(0, lw, n),

Expand Down Expand Up @@ -168,7 +167,7 @@ SunCalc.getTimes = function (date, lat, lng) {

// moon calculations, based on http://aa.quae.nl/en/reken/hemelpositie.html formulas

function moonCoords(d) { // geocentric ecliptic coordinates of the moon
SunCalc.moonCoords = function (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
Expand All @@ -189,9 +188,9 @@ SunCalc.getMoonPosition = function (date, lat, lng) {

var lw = rad * -lng,
phi = rad * lat,
d = toDays(date),
d = SunCalc.toDays(date),

c = moonCoords(d),
c = SunCalc.moonCoords(d),
H = siderealTime(d, lw) - c.ra,
h = altitude(H, phi, c.dec);

Expand All @@ -212,9 +211,9 @@ SunCalc.getMoonPosition = function (date, lat, lng) {

SunCalc.getMoonIllumination = function (date) {

var d = toDays(date),
s = sunCoords(d),
m = moonCoords(d),
var d = SunCalc.toDays(date),
s = SunCalc.sunCoords(d),
m = SunCalc.moonCoords(d),

sdist = 149598000, // distance from Earth to Sun in km

Expand All @@ -231,6 +230,69 @@ SunCalc.getMoonIllumination = function (date) {
};


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) {
var t = new Date(date);
t.setHours(0);
t.setMinutes(0);
t.setSeconds(0);
t.setMilliseconds(0);
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t.setHours(0, 0, 0, 0) instead


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 AMD module / Node module / browser variable
if (typeof define === 'function' && define.amd) define(SunCalc);
else if (typeof module !== 'undefined') module.exports = SunCalc;
Expand Down