Maimonides was a highly intelligent man, somewhere there among other Jewish geniuses like Marx, Einstein and Freud, and as such a genuine rationalist and moralist. This fundamental approach to reality is seen in the way he handles the relationship between Torah and science of his time in The Guide to the Perplexed:: scientific proof, logic and evidence are decisive in correct Philosophy. He does not deny the significance of Divine Revelation so essential to Judaism but sees it as additional information that completes the picture.
Aristotelian geocentric universe
The second book of the Guide begins with the exposition of the physical structure of the universe, as seen by Maimonides. The world-view asserted in the work is essentially Aristotelian, with a spherical earth in the centre, surrounded by concentric Heavenly Spheres.
While Aristotle's view with respect to the eternity of the universe is rejected, Maimonides extensively borrows his proofs of the existence of God and his concepts such as the Prime Mover
Y. Tzvi Langerman writes about his views on astronomy among other things
Maimonides remained attached to the intellectual outlook of the western part of the Islamic world throughout his life, and this is especially true of his work in astronomy. In his youthful search for guidance, especially in matters of cosmography (which were later to be a major concern), he sought out the son of Jābir ibn Aflaḥ as well as some pupils of Ibn Bājja. Indeed, his career affords us one of the clearest examples of the distinctive features of the western Islamic astronomical tradition.
Maimonides contributed to the Arabic astronomical literature by editing (i. e., preparing corrected versions of texts that had become problematic) books written by two of his Andalusian predecessors, the above‐mentioned Jābir and Ibn Hūd, ruler of Seville.
Astronomical issues are stressed at several places in Maimonides' great work of religious thought, the Guide of the Perplexed. The most detailed discussion is found in Part Two, Chapter 24, which is devoted entirely to a review of the state of what may be anachronistically called cosmology or celestial physics.
Aristotelian physics had established by means of what were then taken to be irrefutable proofs that the motions of the heavenly bodies must be circular, with the Earth at the center. Ptolemy's models clearly violate these principles.
All of the solutions that had been offered to date were critically scrutinized and rejected; these included the proposals of Thābit ibn Qurra and Ibn Bājja, for which Maimonides remains our only source.
Visibility of lunar crescent and calendar
Maimonides' sole contribution to mathematical astronomy is his procedure for determining the visibility of the lunar crescent, which takes up several chapters of his great law code, the Mishneh Torah.
Before the calendar was fixed, Jewish law required that the beginning of each month be certified by the court at Jerusalem. No month can exceed 30 days. Hence, if the crescent is not seen on the eve of the 29th, the declaration of the new month is automatic.
Maimonides' procedure is necessary only for those instances where witnesses do report a sighting on the eve of the 29th. Specifically, the members of the court need to know whether a sighting is possible, so that they may convene in the expectation of witnesses; and they need a few details about the appearance of the crescent for purposes of cross‐examination. Conversely, the court needs to know when a sighting will be impossible, so as to be able to reject any purported sightings.
With these facts in mind, it will be readily understood why Maimonides presents his method in “cookbook” fashion. Solar and lunar parameters, listed by Maimonides, can be plugged in, and the computation is then carried out step‐by‐step. Eventually the result is a simple yes or no answer; if the answer is yes, some additional information about the appearance of the crescent can be obtained.
Theoretical explanations or justifications are kept to a bare minimum. Certain parameters, for example the geographical latitude, are built in, since the computation is meant to be true only for Jerusalem and its environs. Maimonides states that he has allowed himself some approximations, but, he assures us, the round‐off errors cancel each other out, so that there is no net effect on the computation.
Religion and science
Maimonides issued some critically important and repercussive statements on the relationship between Judaism and the sciences, astronomy in particular. He asserted that ancient Rabbinic views on the structure of the heavens have no privileged position. The tenets of astronomy can be proven or rejected by universal and invariant rules of logic; hence their source, or, as we might say, the cultural context out of which they emerge, is irrelevant.
On the other hand, astronomy is by no means a “secular” science. Knowledge of God, the attainment of which is a primary religious obligation, can be approximated – Maimonides denies that it can be fully achieved – only by inference from creation. The stars are the most noble bodies in creation, and the study of their motions is one of the most religiously fulfilling activities at our disposal.
Let me repeat something critically important in the paragraphs above describing the views of rabbi Moshe ben Maimon
Knowledge of God, the attainment of which is a primary religious obligation, can be approximated – Maimonides denies that it can be fully achieved – only by inference from creation.
Similar understanding of learning to know God from two books, the Book of Nature and the Book of Grace, is deeply embedded in the theology of Thomas of Aquino who widely quotes Maimonides in his angelic writings.