phases.js

/*
	JavaScript version
	Copyright 2011 Glad Deschrijver <glad.deschrijver@gmail.com>
	with the same license as below.
*/
/*
    This file is part of the kmoon application with explicit permission by the author
    Copyright 1996 Christopher Osburn <chris@speakeasy.org>

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, see <http://www.gnu.org/licenses/>.
*/

.pragma library

/*
** jd.c:
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services, <chris@speakeasy.org>
** Non-commercial usage license granted to all.
**
** convert a Julian Day number to a struct tm
**
** Parameter:
**   double jd:  Julian day number with fraction of day
**
** Returns:
**   struct tm *event_date:  Date-time group holding year, month, day, hour,
**                and minute of the event
*/

function JDtoDate(jd) // convert a Julian Date to a date-time group
{
	var a, a1, z, b, c, d, e;
	var f, day;
	var event_date = new Date();

	jd += 0.5;
	z = Math.floor(jd);
	f = jd - z;

	if (z < 2299161)
	{
		a = z;
	}
	else
	{
		a1 = Math.floor((z - 1867216.25) / 36524.25);
		a = z + 1 + a1 - Math.floor(a1 / 4);
	}

	b = a + 1524;
	c = Math.floor((b - 122.1) / 365.25);
	d = Math.floor(365.25 * c);
	e = Math.floor((b - d)/30.6001);

	day = b - d - Math.floor(30.6001 * e) + f;

	event_date.setDate(1); // dirty hack, otherwise if today is the 31st of a month and the month below is set to a month with < 31 days, then the month is shifted to the next month, e.g. Feb 31 becomes Mar 2; the correct day is set further below
	if (e < 14)
		event_date.setMonth((e - 1) - 1);
	else
		event_date.setMonth((e - 13) - 1);

	if (event_date.getMonth() > (2 - 1))
		event_date.setFullYear(c - 4716);
	else
		event_date.setFullYear(c - 4715);

	event_date.setDate(Math.floor(day));
	day -= event_date.getDate();
	day *= 24;
	event_date.setHours(Math.floor(day));
	day -= event_date.getHours();
	day *= 60;
	event_date.setMinutes(Math.floor(day));
	day -= event_date.getMinutes();
	day *= 60;
	event_date.setSeconds(Math.floor(day));

	return event_date;
}

function DatetoJD(event_date) // convert a date-time group to a JD with fraction
{
	var y, m;
	var d;
	var a, b;
	var jd;

	y = event_date.getFullYear();
	m = event_date.getMonth() + 1;
	d = event_date.getDate() + (event_date.getHours() / 24.0)
	  + (event_date.getMinutes() / 1440.0)
	  + (event_date.getSeconds() / 86400.0);

	if (m == 1 || m == 2)
	{
		y--;
		m += 12;
	}

	a = Math.floor(y / 100);
	b = 2 - a + Math.floor(a / 4);

	if (y < 1583)
		if ((y < 1582) || (m < 10) || ((m == 10) && (d <= 15)))
			b = 0;

	jd = Math.floor(365.25 * (y + 4716)) + Math.floor(30.6001 * (m+1))
	   + d + b - 1524.5;

	return jd;
}

/*
** misc.h
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services,
** Non-commercial usage license granted to all.
**
** Miscellaneous routines for moon phase programs
**
*/

function fmod(x, y)
{
	var n = ((x > 0 && y > 0) || (x < 0 && y < 0)) ? Math.floor(x / y) : Math.ceil(x / y);
	return x - n * y;
}

function torad(x) // convert x to radians
{
	x = fmod(x, 360.0); // normalize the angle
	return ((x) * 0.01745329251994329576); // and return the result
}

/*
** moonphase.c
** 1996/02/11
**
** Copyright 1996, Christopher Osburn, Lunar Outreach Services,
** Non-commercial usage license granted to all.
**
** calculate phase of the moon per Meeus Ch. 47
**
** Parameters:
**    int lun:  phase parameter.  This is the number of lunations
**              since the New Moon of 2000 January 6.
**
**    int phi:  another phase parameter, selecting the phase of the
**              moon.  0 = New, 1 = First Qtr, 2 = Full, 3 = Last Qtr
**
** Return:  Apparent JD of the needed phase
*/

function moonphase(k, phi)
{
	var i;                    // iterator to be named later.  Every program needs an i
	var T;                    // time parameter, Julian Centuries since J2000
	var JDE;                  // Julian Ephemeris Day of phase event
	var E;                    // Eccentricity anomaly
	var M;                    // Sun's mean anomaly
	var M1;                   // Moon's mean anomaly
	var F;                    // Moon's argument of latitude
	var O;                    // Moon's longitude of ascending node
	var A = new Array();      // planetary arguments
	var W;                    // added correction for quarter phases

	T = k / 1236.85;                          // (47.3)

	// this is the first approximation.  all else is for style points!
	JDE = 2451550.09765 + (29.530588853 * k)  // (47.1)
	    + T * T * (0.0001337 + T * (-0.000000150 + 0.00000000073 * T));

	// these are correction parameters used below
	E = 1.0                                   // (45.6)
	  + T * (-0.002516 + -0.0000074 * T);
	M = 2.5534 + 29.10535669 * k              // (47.4)
	  + T * T * (-0.0000218 + -0.00000011 * T);
	M1 = 201.5643 + 385.81693528 * k          // (47.5)
	   + T * T * (0.0107438 + T * (0.00001239 + -0.000000058 * T));
	F = 160.7108 + 390.67050274 * k           // (47.6)
	  + T * T * (-0.0016341 * T * (-0.00000227 + 0.000000011 * T));
	O = 124.7746 - 1.56375580 * k             // (47.7)
	  + T * T * (0.0020691 + 0.00000215 * T);

	// planetary arguments
	A[0]  = 0; // unused!
	A[1]  = 299.77 +  0.107408 * k - 0.009173 * T * T;
	A[2]  = 251.88 +  0.016321 * k;
	A[3]  = 251.83 + 26.651886 * k;
	A[4]  = 349.42 + 36.412478 * k;
	A[5]  =  84.66 + 18.206239 * k;
	A[6]  = 141.74 + 53.303771 * k;
	A[7]  = 207.14 +  2.453732 * k;
	A[8]  = 154.84 +  7.306860 * k;
	A[9]  =  34.52 + 27.261239 * k;
	A[10] = 207.19 +  0.121824 * k;
	A[11] = 291.34 +  1.844379 * k;
	A[12] = 161.72 + 24.198154 * k;
	A[13] = 239.56 + 25.513099 * k;
	A[14] = 331.55 +  3.592518 * k;

	// all of the above crap must be made into radians!!!
	// except for E...

	M = torad(M);
	M1 = torad(M1);
	F = torad(F);
	O = torad(O);

	// all those planetary arguments, too!
	for (i = 1; i <= 14; ++i)
		A[i] = torad(A[i]);

	// ok, we have all the parameters, let's apply them to the JDE.
	// (remember the JDE?  this is a program about the JDE...)

	switch(phi)
	{
		// a special case for each different phase.  NOTE!,
		// I'm not treating these in a 0123 order!!!  Pay
		// attention, there, you!

		case 0: // New Moon
			JDE = JDE
			    - 0.40720         * Math.sin(M1)
			    + 0.17241 * E     * Math.sin(M)
			    + 0.01608         * Math.sin(2.0 * M1)
			    + 0.01039         * Math.sin(2.0 * F)
			    + 0.00739 * E     * Math.sin(M1 - M)
			    - 0.00514 * E     * Math.sin(M1 + M)
			    + 0.00208 * E * E * Math.sin(2.0 * M)
			    - 0.00111         * Math.sin(M1 - 2.0 * F)
			    - 0.00057         * Math.sin(M1 + 2.0 * F)
			    + 0.00056 * E     * Math.sin(2.0 * M1 + M)
			    - 0.00042         * Math.sin(3.0 * M1)
			    + 0.00042 * E     * Math.sin(M + 2.0 * F)
			    + 0.00038 * E     * Math.sin(M - 2.0 * F)
			    - 0.00024 * E     * Math.sin(2.0 * M1 - M)
			    - 0.00017         * Math.sin(O)
			    - 0.00007         * Math.sin(M1 + 2.0 * M)
			    + 0.00004         * Math.sin(2.0 * M1 - 2.0 * F)
			    + 0.00004         * Math.sin(3.0 * M)
			    + 0.00003         * Math.sin(M1 + M - 2.0 * F)
			    + 0.00003         * Math.sin(2.0 * M1 + 2.0 * F)
			    - 0.00003         * Math.sin(M1 + M + 2.0 * F)
			    + 0.00003         * Math.sin(M1 - M + 2.0 * F)
			    - 0.00002         * Math.sin(M1 - M - 2.0 * F)
			    - 0.00002         * Math.sin(3.0 * M1 + M)
			    + 0.00002         * Math.sin(4.0 * M1);
			break;

		case 2: // Full Moon
			JDE = JDE
			    - 0.40614         * Math.sin(M1)
			    + 0.17302 * E     * Math.sin(M)
			    + 0.01614         * Math.sin(2.0 * M1)
			    + 0.01043         * Math.sin(2.0 * F)
			    + 0.00734 * E     * Math.sin(M1 - M)
			    - 0.00515 * E     * Math.sin(M1 + M)
			    + 0.00209 * E * E * Math.sin(2.0 * M)
			    - 0.00111         * Math.sin(M1 - 2.0 * F)
			    - 0.00057         * Math.sin(M1 + 2.0 * F)
			    + 0.00056 * E     * Math.sin(2.0 * M1 + M)
			    - 0.00042         * Math.sin(3.0 * M1)
			    + 0.00042 * E     * Math.sin(M + 2.0 * F)
			    + 0.00038 * E     * Math.sin(M - 2.0 * F)
			    - 0.00024 * E     * Math.sin(2.0 * M1 - M)
			    - 0.00017         * Math.sin(O)
			    - 0.00007         * Math.sin(M1 + 2.0 * M)
			    + 0.00004         * Math.sin(2.0 * M1 - 2.0 * F)
			    + 0.00004         * Math.sin(3.0 * M)
			    + 0.00003         * Math.sin(M1 + M - 2.0 * F)
			    + 0.00003         * Math.sin(2.0 * M1 + 2.0 * F)
			    - 0.00003         * Math.sin(M1 + M + 2.0 * F)
			    + 0.00003         * Math.sin(M1 - M + 2.0 * F)
			    - 0.00002         * Math.sin(M1 - M - 2.0 * F)
			    - 0.00002         * Math.sin(3.0 * M1 + M)
			    + 0.00002         * Math.sin(4.0 * M1);
			break;

		case 1: // First Quarter
		case 3: // Last Quarter
			JDE = JDE
			    - 0.62801         * Math.sin(M1)
			    + 0.17172 * E     * Math.sin(M)
			    - 0.01183 * E     * Math.sin(M1 + M)
			    + 0.00862         * Math.sin(2.0 * M1)
			    + 0.00804         * Math.sin(2.0 * F)
			    + 0.00454 * E     * Math.sin(M1 - M)
			    + 0.00204 * E * E * Math.sin(2.0 * M)
			    - 0.00180         * Math.sin(M1 - 2.0 * F)
			    - 0.00070         * Math.sin(M1 + 2.0 * F)
			    - 0.00040         * Math.sin(3.0 * M1)
			    - 0.00034 * E     * Math.sin(2.0 * M1 - M)
			    + 0.00032 * E     * Math.sin(M + 2.0 * F)
			    + 0.00032 * E     * Math.sin(M - 2.0 * F)
			    - 0.00028 * E * E * Math.sin(M1 + 2.0 * M)
			    + 0.00027 * E     * Math.sin(2.0 * M1 + M)
			    - 0.00017         * Math.sin(O)
			    - 0.00005         * Math.sin(M1 - M - 2.0 * F)
			    + 0.00004         * Math.sin(2.0 * M1 + 2.0 * F)
			    - 0.00004         * Math.sin(M1 + M + 2.0 * F)
			    + 0.00004         * Math.sin(M1 - 2.0 * M)
			    + 0.00003         * Math.sin(M1 + M - 2.0 * F)
			    + 0.00003         * Math.sin(3.0 * M)
			    + 0.00002         * Math.sin(2.0 * M1 - 2.0 * F)
			    + 0.00002         * Math.sin(M1 - M + 2.0 * F)
			    - 0.00002         * Math.sin(3.0 * M1 + M);

			W = 0.00306
			  - 0.00038 * E * Math.cos(M)
			  + 0.00026 * Math.cos(M1)
			  - 0.00002 * Math.cos(M1 - M)
			  + 0.00002 * Math.cos(M1 + M)
			  + 0.00002 * Math.cos(2.0 * F);
			if (phi == 3)
				W = -W;
			JDE += W;
			break;

		default: // oops!
			console.log("The Moon has exploded!");
			exit(1);
			break; // unexecuted code
	}

	// now there are some final correction to everything
	JDE = JDE
	    + 0.000325 * Math.sin(A[1])
	    + 0.000165 * Math.sin(A[2])
	    + 0.000164 * Math.sin(A[3])
	    + 0.000126 * Math.sin(A[4])
	    + 0.000110 * Math.sin(A[5])
	    + 0.000062 * Math.sin(A[6])
	    + 0.000060 * Math.sin(A[7])
	    + 0.000056 * Math.sin(A[8])
	    + 0.000047 * Math.sin(A[9])
	    + 0.000042 * Math.sin(A[10])
	    + 0.000040 * Math.sin(A[11])
	    + 0.000037 * Math.sin(A[12])
	    + 0.000035 * Math.sin(A[13])
	    + 0.000023 * Math.sin(A[14]);

	return JDE;
}

//var LUNATION_OFFSET = 953; // original value, I (Glad) don't know why it was chosen as it slows down the startup of the plasmoid
//var LUNATION_OFFSET = -124; // set lunation start in 2010 (faster startup than with the above)
var LUNATION_OFFSET = 0; // a reasonable start lunation is calculated in lunacalc.js

function moonphasebylunation(lun, phi)
{
	var k = lun - LUNATION_OFFSET + phi / 4.0;
	return moonphase(k, phi);
}