IV. Prediction of the Moon's Motion

" The sun and moon ( are subjected ) to calculations ". Al-Qur'an, Sura 55, verse 5.

How accurate are astronomical calculations ? In other words, is it possible for the actual position of the moon to differ markedly from its predicted position ? This question is a valid one because the accurate prediction of the orbit of the moon was at one time considered a major astronomical problem.

The moon has been studied since the beginnings of civilization, largely for the purpose of the calendar, and it has been known for a very long time that the moon's motion in the sky is not simple. Major irregularities in the motion were observed long before the telescope was invented. As is well known, it was Newton who showed that the motion of the moon around the earth is due to the gravitational attraction between them. He even went on futher to show how the major irregularities observed can be explained by the sun's gravitational pull. This however did not allow him to predict the moon's position with sufficient accurancy (approximately 1 minute of arc) for navigational purpose. The lunar problem plagued Newton and gave him headaches as well as kept him awake at night. It took astronomers some 200 years to perfect the lunar orbit theory which is in use today.