code: def nrel_earthsun_distance(time, how='numpy', delta_t=67.0, numthreads=4):
      
  
      if not isinstance(time, pd.DatetimeIndex):
          try:
              time = pd.DatetimeIndex(time)
          except (TypeError, ValueError):
              time = pd.DatetimeIndex([time, ])
  
      unixtime = np.array(time.astype(np.int64)/10**9)
  
      spa = _spa_python_import(how)
  
      delta_t = delta_t or spa.calculate_deltat(time.year, time.month)
  
      dist = spa.earthsun_distance(unixtime, delta_t, numthreads)
  
      dist = pd.Series(dist, index=time)
  
      return dist
docs: Calculates the distance from the earth to the sun using the
      NREL SPA algorithm described in [1]_.
  
      Parameters
      ----------
      time : pd.DatetimeIndex
  
      how : str, optional, default 'numpy'
          Options are 'numpy' or 'numba'. If numba >= 0.17.0
          is installed, how='numba' will compile the spa functions
          to machine code and run them multithreaded.
  
      delta_t : float, optional, default 67.0
          If delta_t is None, uses spa.calculate_deltat
          using time.year and time.month from pandas.DatetimeIndex.
          For most simulations specifing delta_t is sufficient.
          Difference between terrestrial time and UT1.
          *Note: delta_t = None will break code using nrel_numba,
          this will be fixed in a future version.*
          By default, use USNO historical data and predictions
  
      numthreads : int, optional, default 4
          Number of threads to use if how == 'numba'.
  
      Returns
      -------
      dist : pd.Series
          Earth-sun distance in AU.
  
      References
      ----------
      .. [1] Reda, I., Andreas, A., 2003. Solar position algorithm for solar
         radiation applications. Technical report: NREL/TP-560- 34302. Golden,
         USA, http://www.nrel.gov.