docs: def angular_distance(n1, n2):
      """Return the angular separation between two 3 dimensional vectors.
  
      Parameters
      ----------
      n1, n2: array-like, shape (3,)
          Coordinates of two vectors.
          Their magnitude does not matter.
  
      Returns
      -------
      d_sigma: float
          Angle between n1 and n2 in radians.
      """
      return np.arctan2(vector.vector_mag(np.cross(n1, n2)), np.dot(n1, n2))