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package ru.olamedia.astronomy;
/*
* Copyright 2011 Brad Parks
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//package com.bradsbrain.simpleastronomy;
import java.util.Calendar;
public class SunPosition {
// some handy constants
private double EPOCH = 2447891.5; // 1990 January 0.0
private double ECLIPTIC_LONGITUDE_OF_PERIGREE = 282.768422;
private double ECLIPTIC_LONGITUDE_AT_EPOCH_1990 = 279.403303;
private double ECCENTRICITY_OF_ORBIT = 0.016713;
/**
* The geocentric ecliptic longitude. <br>
* Calculation is good to 3 decimal places <br>
* me: 337.44406603442917, book: 337.444194
*/
private double geoEclipticLongitude = 0; // oft represented as a lambda with
// little circle+dot
/**
* The mean anomaly
*/
private double meanAnomaly = 0; // oft represented as capital M with little
// circle+dot
public SunPosition(Calendar cal) {
Calendar myCal = BaseUtils.getSafeLocalCopy(cal.getTimeInMillis());
double daysSince = BaseUtils.exactDaysSince(myCal, EPOCH);
double N = (360 / 365.242191 * daysSince) % 360;
if (N < 0) {
N += 360;
}
meanAnomaly = computeMeanAnomaly(N);
geoEclipticLongitude = computeGeoEclipticLongitude(N);
}
private double computeGeoEclipticLongitude(double nValue) {
double Ec = (360.0 / Math.PI) * ECCENTRICITY_OF_ORBIT
* Math.sin(Math.toRadians(meanAnomaly));
double preliminaryLongitude = nValue + Ec
+ ECLIPTIC_LONGITUDE_AT_EPOCH_1990;
if (preliminaryLongitude > 360) {
preliminaryLongitude -= 360;
}
return preliminaryLongitude;
}
private double computeMeanAnomaly(double nValue) {
double someMean = nValue + ECLIPTIC_LONGITUDE_AT_EPOCH_1990
- ECLIPTIC_LONGITUDE_OF_PERIGREE;
return someMean < 0 ? someMean + 360 : someMean;
}
/**
* TODO: implement this someday
*/
public RightAscension getRightAscension() {
return null;
}
/**
* TODO: implement this someday
*/
public Declination getDeclination() {
return null;
}
public double getEclipticLongitude() {
return geoEclipticLongitude;
}
public double getMeanAnomaly() {
return meanAnomaly;
}
}
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