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 Sun. 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 Sun { 027 028 private static final double SUN_DISTANCE = 149598000.0; 029 private static final double SUN_MEAN_RADIUS = 695700.0; 030 031 private Sun() { 032 // Utility class without constructor 033 } 034 035 /** 036 * Calculates the equatorial position of the sun. 037 * 038 * @param date 039 * {@link JulianDate} to be used 040 * @return {@link Vector} containing the sun position 041 */ 042 public static Vector positionEquatorial(JulianDate date) { 043 double T = date.getJulianCentury(); 044 double M = PI2 * frac(0.993133 + 99.997361 * T); 045 double L = PI2 * frac(0.7859453 + M / PI2 046 + (6893.0 * sin(M) + 72.0 * sin(2.0 * M) + 6191.2 * T) / 1296.0e3); 047 048 double d = SUN_DISTANCE 049 * (1 - 0.016718 * cos(date.getTrueAnomaly())); 050 051 return Vector.ofPolar(L, 0.0, d); 052 } 053 054 /** 055 * Calculates the geocentric position of the sun. 056 * 057 * @param date 058 * {@link JulianDate} to be used 059 * @return {@link Vector} containing the sun position 060 */ 061 public static Vector position(JulianDate date) { 062 Matrix rotateMatrix = equatorialToEcliptical(date).transpose(); 063 return rotateMatrix.multiply(positionEquatorial(date)); 064 } 065 066 /** 067 * Calculates the horizontal position of the sun. 068 * 069 * @param date 070 * {@link JulianDate} to be used 071 * @param lat 072 * Latitude, in radians 073 * @param lng 074 * Longitute, in radians 075 * @return {@link Vector} of horizontal sun position 076 */ 077 public static Vector positionHorizontal(JulianDate date, double lat, double lng) { 078 Vector mc = position(date); 079 double h = date.getGreenwichMeanSiderealTime() + lng - mc.getPhi(); 080 return equatorialToHorizontal(h, mc.getTheta(), mc.getR(), lat); 081 } 082 083 /** 084 * Returns the angular radius of the sun. 085 * 086 * @param distance 087 * Distance of the sun, in kilometers. 088 * @return Angular radius of the sun, in radians. 089 * @see <a href="https://en.wikipedia.org/wiki/Angular_diameter">Wikipedia: Angular 090 * Diameter</a> 091 */ 092 public static double angularRadius(double distance) { 093 return asin(SUN_MEAN_RADIUS / distance); 094 } 095 096}