MoonPhases.java

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package com.cepmuvakkit.conversion.phaseEvents;

import com.cepmuvakkit.times.posAlgo.Ecliptic;
import com.cepmuvakkit.times.posAlgo.LunarPosition;
import com.cepmuvakkit.times.posAlgo.SolarPosition;

public class MoonPhases {

    private SolarPosition solar;
    private LunarPosition lunar;
    private Ecliptic moonPos, solarPos;

    public MoonPhases() {
        solar = new SolarPosition();
        lunar = new LunarPosition();
    }

    /**
     * searchPhaseEvent the Goal function for search of phase events [-180, 180]
     * Difference between the longitude of the Moon from the Sun and the nominal
     * value for a given phase (New Moon 0, First Quarter 90, New Crescent 8,
     * First Quarter 90, Full Moon 180, Last Quarter 270)
     *
     * @param jd    Julian Day
     * @param ΔT    parameter delta-T (ΔT)
     * @param phase the calculated Moon Phase [in degrees] New Moon=0 New
     *              Crescent=8 First Quarter=90 Full Moon=180 Last Quarter=270
     * @return Difference between the longitude of the Moon from the Sun and the
     * nominal value for a given phase (New Moon 0, First Quarter 90,
     * etc.)
     */
    public double searchPhaseEvent(double jd, double ΔT, int phase) {
        double LongDiff, tau_Sun = 8.32 / (1440.0); // 8.32 min [cy]
        moonPos = lunar.calculateMoonEclipticCoordinates(jd, ΔT);
        solarPos = solar.calculateSunEclipticCoordinatesAstronomic(
                jd - tau_Sun, ΔT);
        LongDiff = moonPos.λ - solarPos.λ;
        if (phase == 8)// Crescent Visibility at 8 degrees Angle
        {
            double elongation = Math.sqrt(LongDiff * LongDiff + moonPos.β
                    * moonPos.β);
            // In case of Small angles of elongation lattitude is
            // taken into root mean square due to accuracy
            return phase - elongation;
        }
        return modulo((LongDiff - phase + 180), 360) - 180;

    }

    /**
     * Modulo: calculates x mod y,
     * <ul
     * x mod y
     * </ul>
     *
     * @param double x, double y
     * @return reminder
     */
    private double modulo(double x, double y) {
        return y * frac(x / y);
    }

    /**
     * Gives the fractional part of a number
     *
     * @param double x
     * @return fractional part of a number
     */
    private double frac(double x) {
        return x - Math.floor(x);
    }
}