docs: def predict(self, date, obs_code=568):
          """
          use the bk predict method to compute the location of the source on the given date.
          """
          time = Time(date, scale='utc', precision=6)
          jd = ctypes.c_double(time.jd)
          # call predict with agbfile, jdate, obscode
          self.orbfit.predict.restype = ctypes.POINTER(ctypes.c_double * 5)
          self.orbfit.predict.argtypes = [ ctypes.c_char_p, ctypes.c_double, ctypes.c_int ]
          predict = self.orbfit.predict(ctypes.c_char_p(self.abg.name),
                         jd,
                         ctypes.c_int(obs_code))
          self.coordinate = coordinates.SkyCoord(predict.contents[0],
                                                 predict.contents[1],
                                                 unit=(units.degree, units.degree))
          self.dra = predict.contents[2]
          self.ddec = predict.contents[3]
          self.pa = predict.contents[4]
          self.date = str(time)