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Compute sun and moon phases
/*
* Shredzone Commons - suncalc
*
* Copyright (C) 2017 Richard "Shred" Körber
* http://commons.shredzone.org
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
*
* This program 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.
*/
package org.shredzone.commons.suncalc.util;
import static java.lang.Math.*;
import static org.shredzone.commons.suncalc.util.ExtendedMath.*;
/**
* Calculations and constants for the Moon.
*
* @see "Astronomy on the Personal Computer, 4th edition
* (Oliver Montenbruck, Thomas Pfleger) -
* ISBN 978-3-540-67221-0"
*/
public final class Moon {
private static final double MOON_MEAN_RADIUS = 1737.1;
private Moon() {
// Utility class without constructor
}
/**
* Calculates the equatorial position of the moon.
*
* @param date
* {@link JulianDate} to be used
* @return {@link Vector} of equatorial moon position
*/
public static Vector positionEquatorial(JulianDate date) {
double T = date.getJulianCentury();
double L0 = frac(0.606433 + 1336.855225 * T);
double l = PI2 * frac(0.374897 + 1325.552410 * T);
double ls = PI2 * frac(0.993133 + 99.997361 * T);
double D = PI2 * frac(0.827361 + 1236.853086 * T);
double F = PI2 * frac(0.259086 + 1342.227825 * T);
double D2 = 2.0 * D;
double l2 = 2.0 * l;
double F2 = 2.0 * F;
double dL = 22640.0 * sin(l)
- 4586.0 * sin(l - D2)
+ 2370.0 * sin(D2)
+ 769.0 * sin(l2)
- 668.0 * sin(ls)
- 412.0 * sin(F2)
- 212.0 * sin(l2 - D2)
- 206.0 * sin(l + ls - D2)
+ 192.0 * sin(l + D2)
- 165.0 * sin(ls - D2)
- 125.0 * sin(D)
- 110.0 * sin(l + ls)
+ 148.0 * sin(l - ls)
- 55.0 * sin(F2 - D2);
double S = F + (dL + 412.0 * sin(F2) + 541.0 * sin(ls)) / ARCS;
double h = F - D2;
double N = -526.0 * sin(h)
+ 44.0 * sin(l + h)
- 31.0 * sin(-l + h)
- 23.0 * sin(ls + h)
+ 11.0 * sin(-ls + h)
- 25.0 * sin(-l2 + F)
+ 21.0 * sin(-l + F);
double l_Moon = PI2 * frac(L0 + dL / 1296.0e3);
double b_Moon = (18520.0 * sin(S) + N) / ARCS;
double dt = 385000.5584
- 20905.3550 * cos(l)
- 3699.1109 * cos(D2 - l)
- 2955.9676 * cos(D2)
- 569.9251 * cos(l2);
return Vector.ofPolar(l_Moon, b_Moon, dt);
}
/**
* Calculates the geocentric position of the moon.
*
* @param date
* {@link JulianDate} to be used
* @return {@link Vector} of geocentric moon position
*/
public static Vector position(JulianDate date) {
Matrix rotateMatrix = equatorialToEcliptical(date).transpose();
return rotateMatrix.multiply(positionEquatorial(date));
}
/**
* Calculates the horizontal position of the moon.
*
* @param date
* {@link JulianDate} to be used
* @param lat
* Latitude, in radians
* @param lng
* Longitute, in radians
* @return {@link Vector} of horizontal moon position
*/
public static Vector positionHorizontal(JulianDate date, double lat, double lng) {
Vector mc = position(date);
double h = date.getGreenwichMeanSiderealTime() + lng - mc.getPhi();
return equatorialToHorizontal(h, mc.getTheta(), mc.getR(), lat);
}
/**
* Returns the angular radius of the moon.
*
* @param distance
* Distance of the moon, in kilometers.
* @return Angular radius of the moon, in radians.
* @see Wikipedia: Angular
* Diameter
*/
public static double angularRadius(double distance) {
return asin(MOON_MEAN_RADIUS / distance);
}
}