This is how the oldest science in the world flourished in Toledo, 1,000 years ago.

Almost 2,000 years ago, in Africa, specifically in the city of Alexandria in Egypt, Claudius Ptolemy wrote a set of thirteen books known as Mathematical Syntax . This Ptolemaic treatise summarized the most widely accepted concept of the universe throughout most of history, only replaced just over 500 years ago, after the Copernican revolution. In those books, the Alexandrian sage described a model in which the Earth was stationary at the center, and the Moon, the other planets, the Sun, and the fixed stars were located in concentric spheres that revolved around the Earth.

This model was intended to explain the position of the Sun and the planets relative to the stars throughout the year. It also sought to explain why there is day and night, seasons, or why the planets—wandering stars, according to the etymology of the word—describe strange movements in the sky. Ptolemy sought to use his model to reproduce observations of the positions of stars that had been made centuries earlier, primarily by other famous Greek astronomers such as Hipparchus of Nicaea.

Ptolemy's work, since it was written around 150 AD, has been transmitted to the present day in an interesting way, which I believe teaches us a lot about the power of science to unite people and cultures without borders, from Africa to Europe and America, passing through Asia. Mathematical Syntax is better known today by the name The Almagest , which comes from the Arabic al-majisṭī —“the greatest,” “the majestic”— because the work that came to us in Europe comes from copies made in Arabic around the 9th century. Perhaps it was earlier, but the oldest known copy is the one made during the time of the Caliph Al-Ma'mun, who reigned in the Abbasid Caliphate —with its capital in Baghdad— between the years 813-833 AD. He seems to have been very fond of science and promoted the translation into Arabic of many Greek works , including a copy of Mathematical Syntax which he obtained after a peace treaty with the Byzantine Empire.

From the Arab world, the now-famous Almagest spread to Europe around the 12th century. Part of the credit for this goes to people living in cities like Toledo. During the 11th and 12th centuries, science flourished here, where Muslim astronomers like Al-Zarqali—also known as Azarquiel, who was born in Toledo and died in Córdoba—followed the teachings of the Almagest and made their own measurements of the positions of the stars. Al-Zarqali built instruments like astrolabes and water clocks (clepsydras) to measure time at night, something extremely important for making these astronomical observations.

In Toledo, Jewish astronomers such as Isaac ben Sid also gathered to learn and make observations. In that city, both Jews and Muslims, who had access to ancient books preserved in Arabic, including the Almagest , read the texts and translated them into the vernacular language, Spanish. Christian monks, scribes, and copyists, such as Gerard of Carmona, hearing these astronomers read books like the Almagest , rewrote them in Latin and the vernacular, not without effort and errors due to a lack of specific knowledge on the subject or errors of interpretation, as well as typographical errors.

Ultimately, it was also in Toledo where—funded by King Alfonso X , already in the 13th century—those texts and all that centuries-old astronomical knowledge would later be captured in the so-called Alfonsine Tables , written in Castilian. These tables were the most important compilation of astronomical data, techniques, and knowledge for several hundred more years. First in handwritten books, then copied by printing. They even reached Copernicus, who supposedly used the Alfonsine Tables, and would end up changing our vision of the universe forever. The knowledge that emerged centuries earlier in Asia Minor (Nicaea or Alexandria), transmitted through Byzantium to the empires of the Near East (Baghdad), reached Europe (Toledo), where it changed the paradigm of millennia; and from here, it was transmitted to the rest of the world.

A long-term intercultural effort

And this is where I want to pause to draw conclusions from this whole story. This week, astrophysicists from multiple countries gathered at an international conference in Toledo, the city known as a melting pot of cultures—not without challenges, given what's been happening around the world in recent months —to present our discoveries and discuss what we know and don't know about how galaxies have formed throughout practically the entire life of the universe. Today, our tables are in electronic format; each person interprets them to their best understanding, with errors and successes. We have also used past knowledge to build incredible instruments: our astrolabes or clepsydras are today telescopes like the James Webb . We transcribe our results in scientific and popular articles, with the help of journalists, today's scribes.

Science continues to transcend time, religions, and cultures, in a way that is not far removed from that era in certain aspects. Basic science—specifically, astronomy—is an endeavor that Isaac ben Sid, in the prologue to the Alfonsine Tables, would say (transforming his words into more contemporary language) that "can only be undertaken by scientists for generations, since discoveries transcend the human lifespan."

A basic science that must be promoted by institutions: the king at that time; today, governments, through public funding from taxes. We must all strive to present its results in language understandable to all of society, in all countries, so that knowledge can be collaboratively advanced, which implies progress in respect for differences, equality, and justice.

Cosmic Void is a section that presents our knowledge of the universe in both qualitative and quantitative terms. It aims to explain the importance of understanding the cosmos not only from a scientific perspective, but also from a philosophical, social, and economic perspective. The name "cosmic void" refers to the fact that the universe is, and is, for the most part, empty, with less than one atom per cubic meter, despite the fact that, paradoxically, there are quintillion atoms per cubic meter in our surroundings, which invites reflection on our existence and the presence of life in the universe. The section is composed of Pablo G. Pérez González , researcher at the Center for Astrobiology, and Eva Villaver , deputy director of the Instituto de Astrofísica de Canarias.