Complex sentence: The precise modeling of the motion of the Moon has because of this been a difficult task, the best and most accurate modeling for the Moon orbit before the availability of digital computers was obtained with the complicated Delunay and Brown's lunar theories.
Split into simpler sentences: The precise modeling of the motion of the Moon has because of this been a difficult task. The best and most accurate modeling for the Moon orbit before the availability of digital computers was obtained with the complicated Delunay and Brown's lunar theories.