def METHOD_NAME(xyz):
    """Convert |xyz| to spherical coordinates (r,theta,phi).
    ``r`` - vector length
    ``theta`` - angle above (+) or below (-) the xy-plane
    ``phi`` - angle around the z-axis
    Note that ``theta`` is an elevation angle measured up and down from
    the xy-plane, not a polar angle measured from the z-axis, to match
    the convention for both latitude and declination.
    """
    r = length_of(xyz)
    x, y, z = xyz
    theta = arcsin(z / (r + _AVOID_DIVIDE_BY_ZERO))
    phi = arctan2(y, x) % tau
    return r, theta, phi