code: def timescale(self, delta_t=None):
          
          if delta_t is not None:
              delta_t_recent = np.array(((-1e99, 1e99), (delta_t, delta_t)))
          else:
              data = self('deltat.data')
              preds = self('deltat.preds')
              data_end_time = data[0, -1]
              i = np.searchsorted(preds[0], data_end_time, side='right')
              delta_t_recent = np.concatenate([data, preds[:,i:]], axis=1)
          leap_dates, leap_offsets = self('Leap_Second.dat')
          return Timescale(delta_t_recent, leap_dates, leap_offsets)
docs: Open or download three time scale files, returning a `Timescale`.
  
          This method is how most Skyfield users build a `Timescale`
          object, which is necessary for building specific `Time` objects
          that name specific moments.
  
          This will open or download the three files that Skyfield needs
          to measure time.  UT1 is tabulated by the United States Naval
          Observatory files ``deltat.data`` and ``deltat.preds``, while
          UTC is defined by ``Leap_Second.dat`` from the International
          Earth Rotation Service.