On the Astrolabe

"But an exhibit a book does not make, for an exhibit is one thing and a book is something slightly different, though both products can in principle convey very significant educational messages in their own different ways." George SalibaLate antiquity scienceAlexandria had become the established center of Ancient world's science and philosophy, by the first century B.C., the towering Pharos of enlightenment with its libraries, and institutions. This meeting place of Hellenist and Oriental philosophies with advanced ancient Egyptian Astronomy, Medicine, Chemical technology, mathematics, and Hermeticism, out of which evolved Neoplatonism, became a crucible of sciences and civilized thought. The Alexandrine heritage systematized and put into dialectical form by the peculiar discursive power of the Greeks, described by the uninformed as Greek science.Passing from Alexandria to Antioch, and from there to Edessa, by the Monophysite Christian and Syriac Nestorians, particularly instrumental in the evolution of learning in Syriac, as far east as Persia. In the third century A.D., King Shapur I of Persia, founded a school, set up on the model of those at Alexandria and Antioch, in a metropolis that became a center of ancient sciences, instructing in Greek and Syriac; astronomy, medicine, mathematics, and logic were taught, mostly from Greek texts translated into Syriac. This school, lasted long after the rise of the Abbasid caliphate, and became an important source of ancient learning in the Islamic world.John Philoponus, a Christian philosopher, scientist, and first Christian dean of the Alexandrian Academy, who lived approximately from 490 to 570, in Alexandria is also known, in Arabic, as Yehya Al Nahawi (The Grammarian) His oeuvre comprises at least 40 items on diverse subjects such as ..., logic, mathematics, physics, psychology, cosmology, astronomy,... even medical treatises have been attributed to him. A substantial part of his work has come down to us, but some treatises are known only indirectly through quotations or translations into Syriac and Arabic, as quoted from Stanford Encyclopedia of Philosophy, wrote on The Astrolabe; Treatise Concerning the use and arrangement of the Astrolabe and the Engravings upon it; "The subject has already been treated sufficiently by my teacher the philosopher Ammonius, but still requires to be further elucidated so that it may be easily apprehended by those also who are not instructed in such matters." Technical Comments“The two straight lines on the plane surface, on which the rule lies, cutting one another in the middle, correspond to the meridian line and the horizon: of these, the one descending from above from the ring whereby we suspend the instrument corresponds to the meridian line in each zone, the other cutting it in two at right angles corresponds to the horizon. On this latter, the one corresponding to the horizon, stands a semi-circle having this line itself as its diameter.This semi-circle corresponds to the hemisphere of the heaven above the earth. This semi-circle is cut in two by the other line, that descending from the ring, which we said corresponded to the meridian line, the cutting taking place by the upper end of the line near the ring. Each of the quadrants on either side has been divided into 90 degrees, on which the index of the rule falls, and thereby we determine the meridian height above the horizon of the sun, or any other star, how many degrees each hour it has been raised above the rising or the setting horizon.The ninetieth degree indicates the Sign at the summit in the case of each House, and the first [degree] what is next to the horizon itself, whether the rising or the setting one, as the using of the instrument will teach us as we proceed. It is not the case, however, that in all astrolabes both quadrants have been divided into the ninety degrees, but only one of them, for one, whichever it happens to be, is enough for our observing. For it is possible to know by either [quadrant] how far the sun, or any other star, has been raised from the setting or from the rising horizon. But that we may find it easy to observe when the instrument is suspended with either hand, in some cases both the quadrants have been engraved.”