Claudio Ptolomeo, the great Greco-Roman scholar of the second century AD, gave us his “Geography” and “Almagest”, which had a huge impact on astronomy and geography for more than 1000 years in the imagination and knowledge of the West and the Islamic world. He made an extraordinary synthesis of knowledge accumulated during previous centuries, which provided the basis for the cosmography of the educated man. But his intellectual activity did not stop there: we also know other works thanks to later references, or their re-workings, in fields ranging from astronomy to music, or even optics. However, as a man of his time, he did not dissociated himself completely from activities outside the scope of rationality. And indeed, one of his most influential works during the Middle Ages was the “Tetrabiblos” or “Apotelesmatika“, known in Latin as “Quadripartitum“, which essentially deals with astrology .
Astronomy and astrology: the origin of the difference
The “Tetrabiblio“ was essentially unknown to Western civilization during the High Middle Ages. Its subsequent “popularity” can be attributed to the Islamic culture , as the Middle East helds this manual as the reference par excellence for these art forms. Unfortunately, it spread to the West due to the translations from Toledo and elsewhere, most notably from Barcelona, becoming a huge success and one of the justifications for this art form. Thus, astrology and astronomy were placed at similar level and at second, with its huge predictive ability, seemed to validate and justify the first. Despite this, Ptolemy himself separated them, stating in “Tetrabiblios” that astronomy was a mathematical science while the latter could not expect the same kind of results . In any case, both activities indiscriminately exchanged names until the fifteenth century, and in fact astrology was taught as a scientific discipline in European universities until the mid-seventeenth century, when telescopes were being used, even though the supposed intellectual apparatus had been dismissed by true science, from both a theoretical and an observational point of view.
Even though there were numerous attacks against this type of superstition, it’s more than likely that the most effective attack came from the humanist Giovanni Pico della Mirandola, who was a key figure during the Renaissance.
Born in 1463 and deceased at the age of 31, Pico della Mirandola’s intellect, despite his early death, created and continues to do, an eclectic view of the world, centered on man and his dignity. In 1486 he published “Conclusiones philosophicae, cabalisticae et theologicae”, better know as “The 900 theses”, a syncretic text between different religious interpretations. That same year he published “Oratio de hominis dignitate” (“Oration on the Dignity of Man”), which has come to be known as The manifesto of the Renaissance, and is divided into three sections that are still very current: the right to dissent, respect for religious and cultural diversity, and the tribute due to individuality. This shows us his pursuit of knowledge within a Neo-Platonism framework that does not neglect other schools of thought. He was condemned as a heretic due to several of his theses, but ended up being pardoned by Pope Alexander IV.
Pico della Mirandola amassed an extraordinary library, which he bequeathed with the proviso that it did not end up in a religious institution. Nevertheless, it was sold four years after his death, in 1498, to Cardinal Domenico Grimani. The manifesto states that it contained at least 1190 very eclectic titles that made up one of the largest private libraries in the world, and included text in Latin, Greek, Hebrew, Aramaic and Arabic. 
His attack on astrology, “Disputationes adversus astrologiam divinatricem”, is based on the free will of man. Amongst other tools, he uses Ptolomeo himself to break apart the fallacy that astrology represents. However, the attacks from the point of view of humanism and rationality weren’t enough, and astrology continued to be taught in higher educational centers. One example comes from the University of Pisa, one of the most influential universities at that time. When Cosimo I de Medici re-founded the university in 1543 (the year that Copernico published “De revolutionibus”) the statutes were rewritten. They stated that Ptolomeo was to be taught in third year mathematics, although it didn’t say which one of the scholar’s books would be taught. Therefore, Monk Filippo Fantoni, who taught at the university between 1560 and 1567, and then again between 1582 and 1589, chose “Tetrabiblios” for his course, which dealt with astrology. A clear example of poorly understood academic freedom. Fortunately there was wind blowing from other corners, and it didn’t take long until a storm blew away the chicanery, at least within the academic world. In fact, Fantoni was replaced by Galileo, a pioneer of the 17th century scientific revolution.
Science vs. superstition in the stars
The truth is that numerous reputable scientists made use of astrology. In many cases clearly showing their skepticism, or simply as a means to earn a living or as a condition of their court position. One of the best know was Johannes Kepler, who lived between the 16th and 17th century. Kepler, who together with Galileo Galilei revolutionized celestial mechanics, and therefore the cosmological interpretation of reality, called astrology the “stepchild” of astronomy, although the term “bastard” would have fit better. Later on, he left us a gem that left no doubt about his own view of the situation:
“When a spirit accustomed to mathematical deduction is faced with false foundations [of astrology], they strongly resist, for a long time, like a stubborn mule, to set foot in that dirty puddle, until they are forced to do so with blows and curses.” 
Unfortunately, superstition is still strongly rooted among different sections of the population, even among those considered to be educated, as well as having a significant presence in various media. Palpable proof that the Renaissance Humanism and its natural heir, Enlightenment, have failed to fully succeed. And indeed, culture is an extremely fragile phenomenon, as clearly demonstrated by the terrible loss of diversity that occurred recently with the destruction of World Heritage in Syria and Iraq. Today, it seems that the hype is moving us further and further away from the ideal of being comprehensive and rational human beings. When technique becomes a golden idol, it seems that a humanist science that responds to people’s needs is more necessary than ever. Therefore, comprehensive education still has a long way to go.
David Barrado Navascués
CAB, INTA-CSIC, European Space Astronomy Center (ESAC, Madrid)
-  “Cuatro libros”, “Efectos” and “Cuatro partes”, respectively.
-  Heilem, S., “Ptolemy’s Doctrine of the Terms and Its Reception”, in “Ptolomeo in Perspective”, Alexander Jones Eds., Archimedes, vol. 23, Sprinter 2010.
-  To be more precise, the phase is “The first of these, which has its own science, desirable in itself even though it does not attain the result given by the second [astrology], has been expounded to you as best we could in its own treatise [Almagesto].” Stated in Rutkin, H.D., “The Use and Abuse of Ptolemy’s Tetrabiblos in Renaissance and Early Modern Europe: Two Case Studies (Giovanni Pico della Mirandola and Filippo Fantoni)”, in “Ptolomeo in Perspective”, Alexander Jones Eds., Archimedes, vol. 23, Sprinter 2010.
-  Ashley-Montagu , M.F., “The Library of Pico Della Mirandola by Pearl Kibre”, Isis, Vol. 26, No. 1, 1936, The University of Chicago Press
-  Kepler, J., “De Stella nova in pede Serpentarii”, G.W., Vol. I, p. 147seq., citado from Koestler, A., “The Sleepwalkers. A history of man’s changing vision of the Universe”, the Macmillan company, 1959