iau1980.py 文件源码

def equinox(date, eop_correction=True, terms=106, kinematic=True):
    """Equinox equation in degrees
    """
    epsilon_bar, delta_psi, delta_eps = _nutation(date, eop_correction, terms)

    equin = delta_psi * 3600. * np.cos(np.deg2rad(epsilon_bar))

    if date.d >= 50506 and kinematic:
        # Starting 1992-02-27, we apply the effect of the moon
        ttt = date.change_scale('TT').julian_century
        om_m = 125.04455501 - (5 * 360. + 134.1361851) * ttt\
            + 0.0020756 * ttt ** 2 + 2.139e-6 * ttt ** 3

        equin += 0.00264 * np.sin(np.deg2rad(om_m)) + 6.3e-5 * np.sin(np.deg2rad(2 * om_m))

    # print("esquinox = {}\n".format(equin / 3600))
    return equin / 3600.