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Return the obliquity of the ecliptic (the angle between the ecliptic and the earth's equator) at the current time. This varies due to the precession of the earth's axis.

Returns:
the obliquity of the ecliptic relative to the equator, measured in radians.

Definition at line 1403 of file astro.cpp.

References getJulianDay().

Referenced by eclipticToEquatorial().

                                             {
    if (isINVALID(eclipObliquity)) {
        const double epoch = 2451545.0;     // 2000 AD, January 1.5

        double T = (getJulianDay() - epoch) / 36525;

        eclipObliquity = 23.439292
            - 46.815/3600 * T
            - 0.0006/3600 * T*T
            + 0.00181/3600 * T*T*T;

        eclipObliquity *= DEG_RAD;
    }
    return eclipObliquity;
}

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