coordinates.py 文件源码

def ra_distance(declination, ra_a, ra_b):

    """
    This function ...
    :param declination: dec in degrees
    :param ra_a: ra in degrees
    :param ra_b: ra in degrees
    :return:
    """

    cos_ra_distance = np.sin(np.radians(declination))**2 + np.cos(np.radians(declination))**2 * np.cos(np.radians(ra_b-ra_a))

    if cos_ra_distance > 1.0 and np.isclose(cos_ra_distance, 1.0): cos_ra_distance = 1.0 # Avoid crashes of np.arcos

    # Return ...
    return np.degrees(np.arccos(cos_ra_distance))

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