Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;

public class Main {
    /**
     * Calculate the difference between true solar time and mean. The "equation
     * of time" is a term accounting for changes in the time of solar noon for
     * a given location over the course of a year. Earth's elliptical orbit and
     * Kepler's law of equal areas in equal times are the culprits behind this
     * phenomenon. See the
     * <A HREF="http://www.analemma.com/Pages/framesPage.html">Analemma page</A>.
     * Below is a plot of the equation of time versus the day of the year.
     *
     * <P align="center"><img src="doc-files/EquationOfTime.png"></P>
     *
     * @param  t number of Julian centuries since J2000.
     * @return Equation of time in minutes of time.
     */
    private static double equationOfTime(final double t) {
        double eps = Math.toRadians(obliquityCorrected(t));
        double l0 = Math.toRadians(sunGeometricMeanLongitude(t));
        double m = Math.toRadians(sunGeometricMeanAnomaly(t));
        double e = eccentricityEarthOrbit(t);
        double y = Math.tan(eps / 2);
        y *= y;

        double sin2l0 = Math.sin(2 * l0);
        double cos2l0 = Math.cos(2 * l0);
        double sin4l0 = Math.sin(4 * l0);
        double sin1m = Math.sin(m);
        double sin2m = Math.sin(2 * m);

        double etime = y * sin2l0 - 2 * e * sin1m + 4 * e * y * sin1m * cos2l0 - 0.5 * y * y * sin4l0
                - 1.25 * e * e * sin2m;

        return Math.toDegrees(etime) * 4.0;
    }

    /**
     * Calculate the corrected obliquity of the ecliptic.
     *
     * @param  t number of Julian centuries since J2000.
     * @return Corrected obliquity in degrees.
     */
    private static double obliquityCorrected(final double t) {
        final double e0 = meanObliquityOfEcliptic(t);
        final double omega = Math.toRadians(125.04 - 1934.136 * t);
        return e0 + 0.00256 * Math.cos(omega);
    }

    /**
     * Calculate the Geometric Mean Longitude of the Sun.
     * This value is close to 0 degree at the spring equinox,
     * 90 degree at the summer solstice, 180 degree at the automne equinox
     * and 270 degree at the winter solstice.
     *
     * @param  t number of Julian centuries since J2000.
     * @return Geometric Mean Longitude of the Sun in degrees,
     *         in the range 0 degree (inclusive) to 360 degree (exclusive).
     */
    private static double sunGeometricMeanLongitude(final double t) {
        double L0 = 280.46646 + t * (36000.76983 + 0.0003032 * t);
        L0 = L0 - 360 * Math.floor(L0 / 360);
        return L0;
    }

    /**
     * Calculate the Geometric Mean Anomaly of the Sun.
     *
     * @param  t number of Julian centuries since J2000.
     * @return Geometric Mean Anomaly of the Sun in degrees.
     */
    private static double sunGeometricMeanAnomaly(final double t) {
        return 357.52911 + t * (35999.05029 - 0.0001537 * t);
    }

    /**
     * Calculate the eccentricity of earth's orbit. This is the ratio
     * {@code (a-b)/a} where <var>a</var> is the semi-major axis
     * length and <var>b</var> is the semi-minor axis length.   Value
     * is 0 for a circular orbit.
     *
     * @param  t number of Julian centuries since J2000.
     * @return The unitless eccentricity.
     */
    private static double eccentricityEarthOrbit(final double t) {
        return 0.016708634 - t * (0.000042037 + 0.0000001267 * t);
    }

    /**
     * Calculate the mean obliquity of the ecliptic.
     *
     * @param  t number of Julian centuries since J2000.
     * @return Mean obliquity in degrees.
     */
    private static double meanObliquityOfEcliptic(final double t) {
        final double seconds = 21.448 - t * (46.8150 + t * (0.00059 - t * (0.001813)));
        return 23.0 + (26.0 + (seconds / 60.0)) / 60.0;
    }
}