code: def earthsun_distance(unixtime, delta_t, numthreads):
      
  
      R = solar_position(unixtime, 0, 0, 0, 0, 0, delta_t,
                         0, numthreads, esd=True)[0]
  
      return R
docs: Calculates the distance from the earth to the sun using the
      NREL SPA algorithm described in [1].
  
      Parameters
      ----------
      unixtime : numpy array
          Array of unix/epoch timestamps to calculate solar position for.
          Unixtime is the number of seconds since Jan. 1, 1970 00:00:00 UTC.
          A pandas.DatetimeIndex is easily converted using .astype(np.int64)/10**9
      delta_t : float
          Difference between terrestrial time and UT. USNO has tables.
      numthreads : int
          Number to threads to use for calculation (if using numba)
  
      Returns
      -------
      R : array
          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.