-
Notifications
You must be signed in to change notification settings - Fork 411
/
suncalc.js
317 lines (219 loc) · 8.9 KB
/
suncalc.js
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
/*
(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; }
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;
}());