001/* 002 * Shredzone Commons - suncalc 003 * 004 * Copyright (C) 2017 Richard "Shred" Körber 005 * http://commons.shredzone.org 006 * 007 * Licensed under the Apache License, Version 2.0 (the "License"); 008 * you may not use this file except in compliance with the License. 009 * 010 * This program is distributed in the hope that it will be useful, 011 * but WITHOUT ANY WARRANTY; without even the implied warranty of 012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 013 */ 014package org.shredzone.commons.suncalc.util; 015 016import static java.lang.Math.*; 017import static org.shredzone.commons.suncalc.util.ExtendedMath.*; 018 019/** 020 * Calculations and constants for the Moon. 021 * 022 * @see "Astronomy on the Personal Computer, 4th edition 023 * (Oliver Montenbruck, Thomas Pfleger) - 024 * ISBN 978-3-540-67221-0" 025 */ 026public final class Moon { 027 028 private static final double MOON_MEAN_RADIUS = 1737.1; 029 030 private Moon() { 031 // Utility class without constructor 032 } 033 034 /** 035 * Calculates the equatorial position of the moon. 036 * 037 * @param date 038 * {@link JulianDate} to be used 039 * @return {@link Vector} of equatorial moon position 040 */ 041 public static Vector positionEquatorial(JulianDate date) { 042 double T = date.getJulianCentury(); 043 double L0 = frac(0.606433 + 1336.855225 * T); 044 double l = PI2 * frac(0.374897 + 1325.552410 * T); 045 double ls = PI2 * frac(0.993133 + 99.997361 * T); 046 double D = PI2 * frac(0.827361 + 1236.853086 * T); 047 double F = PI2 * frac(0.259086 + 1342.227825 * T); 048 double D2 = 2.0 * D; 049 double l2 = 2.0 * l; 050 double F2 = 2.0 * F; 051 052 double dL = 22640.0 * sin(l) 053 - 4586.0 * sin(l - D2) 054 + 2370.0 * sin(D2) 055 + 769.0 * sin(l2) 056 - 668.0 * sin(ls) 057 - 412.0 * sin(F2) 058 - 212.0 * sin(l2 - D2) 059 - 206.0 * sin(l + ls - D2) 060 + 192.0 * sin(l + D2) 061 - 165.0 * sin(ls - D2) 062 - 125.0 * sin(D) 063 - 110.0 * sin(l + ls) 064 + 148.0 * sin(l - ls) 065 - 55.0 * sin(F2 - D2); 066 067 double S = F + (dL + 412.0 * sin(F2) + 541.0 * sin(ls)) / ARCS; 068 double h = F - D2; 069 double N = -526.0 * sin(h) 070 + 44.0 * sin(l + h) 071 - 31.0 * sin(-l + h) 072 - 23.0 * sin(ls + h) 073 + 11.0 * sin(-ls + h) 074 - 25.0 * sin(-l2 + F) 075 + 21.0 * sin(-l + F); 076 077 double l_Moon = PI2 * frac(L0 + dL / 1296.0e3); 078 double b_Moon = (18520.0 * sin(S) + N) / ARCS; 079 080 double dt = 385000.5584 081 - 20905.3550 * cos(l) 082 - 3699.1109 * cos(D2 - l) 083 - 2955.9676 * cos(D2) 084 - 569.9251 * cos(l2); 085 086 return Vector.ofPolar(l_Moon, b_Moon, dt); 087 } 088 089 /** 090 * Calculates the geocentric position of the moon. 091 * 092 * @param date 093 * {@link JulianDate} to be used 094 * @return {@link Vector} of geocentric moon position 095 */ 096 public static Vector position(JulianDate date) { 097 Matrix rotateMatrix = equatorialToEcliptical(date).transpose(); 098 return rotateMatrix.multiply(positionEquatorial(date)); 099 } 100 101 /** 102 * Calculates the horizontal position of the moon. 103 * 104 * @param date 105 * {@link JulianDate} to be used 106 * @param lat 107 * Latitude, in radians 108 * @param lng 109 * Longitute, in radians 110 * @return {@link Vector} of horizontal moon position 111 */ 112 public static Vector positionHorizontal(JulianDate date, double lat, double lng) { 113 Vector mc = position(date); 114 double h = date.getGreenwichMeanSiderealTime() + lng - mc.getPhi(); 115 return equatorialToHorizontal(h, mc.getTheta(), mc.getR(), lat); 116 } 117 118 /** 119 * Returns the angular radius of the moon. 120 * 121 * @param distance 122 * Distance of the moon, in kilometers. 123 * @return Angular radius of the moon, in radians. 124 * @see <a href="https://en.wikipedia.org/wiki/Angular_diameter">Wikipedia: Angular 125 * Diameter</a> 126 */ 127 public static double angularRadius(double distance) { 128 return asin(MOON_MEAN_RADIUS / distance); 129 } 130 131}