code: def tdb_minus_tt(jd_tdb):
      
      t = (jd_tdb - T0) / 36525.0
  
      # USNO Circular 179, eq. 2.6.
      return (0.001657 * sin ( 628.3076 * t + 6.2401)
            + 0.000022 * sin ( 575.3385 * t + 4.2970)
            + 0.000014 * sin (1256.6152 * t + 6.1969)
            + 0.000005 * sin ( 606.9777 * t + 4.0212)
            + 0.000005 * sin (  52.9691 * t + 0.4444)
            + 0.000002 * sin (  21.3299 * t + 5.5431)
            + 0.000010 * t * sin ( 628.3076 * t + 4.2490))
docs: Computes how far TDB is in advance of TT, given TDB.
  
      Given that the two time scales never diverge by more than 2ms, TT
      can also be given as the argument to perform the conversion in the
      other direction.