To the editors:

One would have to search far and wide to find a historical figure more at the center of intercultural exchange in the sciences than Ibn al-Zarqālluh. His astronomical legacy is diverse: he relied on theories whose origins were Greek (especially Ptolemy’s Almagest), Indo-Iranian (through al-Khwārizmī’s zīj), and Babylonian (using their goal-year cycles to construct a perpetual almanac). He lived at a time and place of great cultural ferment, with Muslim, Jewish, and Christian scholars living and working side by side—although, as Julio Samsó has demonstrated, the western Islamic astronomical community had become largely isolated from their counterparts in the east by Ibn al-Zarqālluh’s time. This was largely due to political disunity that discouraged journeys to the east. Questions of how science is influenced by cultural norms and practices can be explored richly by studying Al-Andalus and the Maghrib. It is a pity that such a pivotal figure as Ibn al-Zarqālluh is not known more widely. To a great extent, we have Samsó and his school in Barcelona to thank that this story is now available in such depth.

With such a dramatic mosaic as a backdrop, one might question exactly what is meant by the term science in the first place. Even in broad outline, our notion of what we describe as a scientist today is no more than a couple of centuries old. What is one to make of a science described in Samsó’s article that includes astrology, and, as he has written elsewhere, folk traditions and even magic? This is a challenge that faces historians especially of premodern science every day. Thankfully, while we continue to struggle with these issues, Samsó and his colleagues have been operating since the beginning with perhaps the best answer of all: allow the historical figures to tell us what science meant to them.

With this perspective, there is really no question whether we should study Andalusī astrology. The Andalusīs did; at least, as Samsó puts it, the more open-minded authorities did. It was a central motivator for improvements in astronomical theories, for the streamlining of calculations, and for the development of astronomical instruments. Without intimate knowledge of topics such as the astrological houses and projection of the rays, we really cannot understand why the astronomers did what they did. Here, then, I may go further than some of my colleagues in arguing that we need to know more of the less technical art of astrological prediction: by separating what we would call pseudoscience from our study, we are fracturing what was not fractured at the time.

Something similar can be said for several serious objects of inquiry in Andalusī astronomy that turned out to be wrong. We read in Samsó’s article of Ibn al-Zarqālluh’s theories of trepidation of the equinoxes, which accounted for the belief that the precession of the equinoxes did not occur at a constant rate, and that the angle between the ecliptic and the equator varies in a periodic fashion. As Samsó notes, this was justified based on what survived of ancient observations. It turned out to be wrong. Something similar can be said of Ibn al-Zarqālluh’s solar model with varying eccentricity. We do not study the history of science to determine winners and losers in the game of truth. Rather, we wish to understand what it means for humans to explore their world, how their cultural backgrounds and political situations affect their activities, how their individual natures make a difference to their crafts, and how the resulting science feeds back into an evolving culture.

Samsó has known this all along, and he presents here some of the information he has gathered through decades of respect for and attention to the people and societies that he has made a career of studying. We would do well to follow his example.