001 /*
002 * $Id: Sidereal.java,v 1.3 2012/02/19 17:35:39 davep Exp $
003 *
004 * This file is part of McIDAS-V
005 *
006 * Copyright 2007-2012
007 * Space Science and Engineering Center (SSEC)
008 * University of Wisconsin - Madison
009 * 1225 W. Dayton Street, Madison, WI 53706, USA
010 * https://www.ssec.wisc.edu/mcidas
011 *
012 * All Rights Reserved
013 *
014 * McIDAS-V is built on Unidata's IDV and SSEC's VisAD libraries, and
015 * some McIDAS-V source code is based on IDV and VisAD source code.
016 *
017 * McIDAS-V is free software; you can redistribute it and/or modify
018 * it under the terms of the GNU Lesser Public License as published by
019 * the Free Software Foundation; either version 3 of the License, or
020 * (at your option) any later version.
021 *
022 * McIDAS-V is distributed in the hope that it will be useful,
023 * but WITHOUT ANY WARRANTY; without even the implied warranty of
024 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
025 * GNU Lesser Public License for more details.
026 *
027 * You should have received a copy of the GNU Lesser Public License
028 * along with this program. If not, see http://www.gnu.org/licenses.
029 */
030
031 package edu.wisc.ssec.mcidasv.data.adde.sgp4;
032
033 /**
034 *
035 * @author Shawn
036 */
037 public class Sidereal
038 {
039
040 /**
041 * Calculates the Greenwich mean sidereal time (GMST) on julDate (doesn't have to be 0h).
042 * Used calculations from Meesus 2nd ed.
043 * @param mjd Modified Julian Date
044 * @return Greenwich mean sidereal time in degrees (0-360)
045 */
046 public static double Greenwich_Mean_Sidereal_Deg(double mjd)
047 {
048 // calculate T
049 double T = (mjd-51544.5)/36525.0;
050
051 // do calculation
052 double gmst = ( (280.46061837 + 360.98564736629*(mjd-51544.5)) + 0.000387933*T*T - T*T*T/38710000.0) % 360.0;
053
054 // make positive
055 if(gmst < 0)
056 {
057 gmst += 360.0;
058 }
059
060 return gmst;
061 } //Greenwich_Mean_Sidereal_Deg
062
063 /**
064 * Calculates the mean sidereal time (MST) on julDate (doesn't have to be 0h) for a given longitiude.
065 * @param mjd Modified Julian Date
066 * @param longitude longitude in degrees
067 * @return mean sidereal time in degrees (0-360)
068 */
069 public static double Mean_Sidereal_Deg(double mjd, double longitudeDeg)
070 {
071 return (Greenwich_Mean_Sidereal_Deg(mjd) + longitudeDeg) % 360.0;
072 } // Mean_Sidereal_Deg
073
074
075 // main testing function
076 public static void main(String[] args)
077 {
078 double mjd = 2449991.875 - AstroConst.JDminusMJD;
079 double longitude = -75; // degrees
080 double latitude = 40;
081
082 double mst = Sidereal.Mean_Sidereal_Deg(mjd, longitude);
083
084 System.out.println("For Phily MST: " + mst);
085
086 // assuming a spherical Earth - calculate ECI vector
087 double [] eciVec = new double[3];
088 eciVec[2] = AstroConst.R_Earth * Math.sin( latitude*Math.PI/180.0 );
089 double r = AstroConst.R_Earth * Math.cos( latitude*Math.PI/180.0 );
090 eciVec[0] = r * Math.cos(mst*Math.PI/180.0);
091 eciVec[1] = r * Math.sin(mst*Math.PI/180.0);
092
093 System.out.println("ECI: " + eciVec[0] + ", " + eciVec[1] + ", " + eciVec[2]);
094 }
095
096 }