Abraham Zacuto helped two countries to become among the richest and most powerful nations on earth. Yet he was kicked out of both. This is the story of how one person’s genius contributed to the conquering of new lands—and how intolerance of his people forced him, too, to travel unchartered territory.

When Spain expelled its Jewish population in 1492, hundreds of thousands of Jews made the trip to neighboring Portugal, where they were granted asylum in return for payment. Among the many who made the trip was Abraham Zacuto, an astronomer and university lecturer who would leave his mark on Portugal just as he had done in Spain.

Today, the title university lecturer might not sound very glamorous. And “astronomer” might sound faintly ridiculous. But in the 15th century, Zacuto was a pretty big deal. Just as today, new knowledge and technologies could transform societies and bring nations riches—but back then, astronomy was an area of immense progress. So it was that Zacuto, who was a superstar astronomer, arrived in Lisbon with a strong reputation.

He had not only taught astronomy at universities and become well known in academic circles in Spain, he had developed a new technology and techniques that could be used to explore the world. This was the dawning of the age of exploration in Europe, and Zacuto was a major factor in its development.

Abraham Zacuto was born in Salamanca in the northwest of Spain in 1452. Salamanca remains an important university town, as it was in the 15th century. Founded in 1218, the University of Salamanca at which Zacuto studied and taught is the oldest university in Spain and the fourth oldest in the western world.

The famous university town was a place of much Jewish and Christian learning, and interreligious relations were relatively good with Jews permitted to live, pray and learn according to their beliefs. Well-to-do Jews, such as the Zacuto family, could receive both a traditional Jewish religious education and a secular education. This meant that Zacuto, whose family was among Salamanca’s Jewish nobility, received a similar education to his non-Jewish peers, and he became known as an astounding intellect among the Christian scholars of the day. Meanwhile, he was also a prominent Jewish leader, ordained as a rabbi.

In the 15th and 16th centuries, Salamanca was home to many of the most important intellectuals in Europe and pioneered the study of many disciplines. While he was at the university, Zacuto’s field of astronomy was undergoing a revival. After years of stagnation in medieval Europe, it was seen as an important field. Finally, in the world of astronomy, Europe was catching up with the Islamic world and China, where it had flourished for centuries.

The Bishop of Salamanca was very interested in astronomy and arranged for Zacuto to take up a position as professor of astronomy and mathematics at the University of Salamanca. As a way of thanking the bishop, Zacuto dedicated his first published astronomical work to him. The book was well received and contained more practicable information than the typical academic text, for it provided travelers and explorers with a means of plotting their route based on astronomy. Zacuto also developed a new type of astrolabe, a device that could be used to find out where one was by measuring the altitude of the sun at noon.

His first publication became Zacuto’s magnus opus and contained 65 detailed yet easy-to-use astronomical tables to determine one’s latitude while at sea. The almanac was first published in Hebrew but was soon translated to Spanish (Castilian) and immediately revolutionized ocean travel. And this was a big deal, as navigating the seas was of paramount importance to European nations during the age of exploration that would precipitate their colonization of the New World and beyond.

So Zacuto’s subject was very much du jour when he was teaching astronomy at the universities of Salamanca, Cartagena and Zaragoza. However what wasn’t en vogue in late 15th century Spain was being Jewish and despite his prominence, Zacuto faced an ultimatum when the Spanish Inquisition reached its apotheosis: convert, be killed or leave. Like thousands of others he chose to leave Spain. In so doing he was a part of the exodus of Iberian Jews that led to the growth of Sephardi communities in the Americas, North Africa and the Ottoman Empire.

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In leaving Spain, Zacuto—like countless others—had to give up his home and material possessions. If they had sufficient gold, however, King John II of Portugal would allow Spanish Jews to settle in his lands for payment. So hundreds of thousands of Jews fled Spain and settled in Portugal to start new lives.

Ironically, in the same year that Spain expelled its Jews, 1492, Christopher Columbus had journeyed from Spain to the Americas under the sponsorship of the Crown of Castile—and using Zacuto’s tools. So King John II saw that Zacuto could benefit his country and its explorers with his knowledge, and the Portuguese king invited him to court as a royal astronomer.

Zacuto arrived in Portugal at a pivotal moment in its history. The country was exploiting its Atlantic coastline and naval tradition to develop wealth and power through trade and conquest. As part of this exploration, the explorer Vasco de Gama was planning to voyage to the legendarily rich lands of India. And when he made his maiden trip there in 1497, he used Zacuto’s tables and charts.

De Gama and other Portuguese explorers would also use Zacuto’s tools when sailing to Brazil and the Americas. In fact, Zacuto briefed and prepared Vasco de Gama and his crew before their voyages, teaching them how to use the tools. The Portuguese king even asked Zacuto for his advice regarding the practicability of de Gama’s proposed trips, to which Zacuto gave his approval, and ships used for the expedition were fitted out with Zacuto’s newly perfected astrolabe, which was the first to be made of iron instead of wood.

But although he contributed greatly to his new country, Zacuto’s work did not insulate him from anti-Jewish forces in Portugal. King Manuel succeeded John II and decided to marry Infanta Isabella of Aragon, the daughter of Ferdinand of Aragon and Isabella of Castile, the monarchs who had expelled Jews from Spain. But Ferdinand and Isabella would only agree to their daughter’s marriage to Manuel—which would unite the crowns of Spain and Portugal—if he would no longer tolerate the Jews in Portugal. So as part of the marriage contract Manuel agreed to persecute Portuguese Jews and to establish a Portuguese Inquisition.

In December 1496, all Jews in Portugal were faced with a heartbreaking ultimatum: convert to Christianity or leave Portugal without their children. Those who chose to leave could only do so on specific ships sanctioned by the king. When Jews would arrive to board their ships, crown officials would put them under immense pressure to convert and stay in the country. Nevertheless, many did manage to leave, including Abraham Zacuto and his grown son Samuel.

Zacuto father and son fled to North Africa. But while en route their ship was twice captured and held for ransom. Finally, they made it to the port of Tunis, where in 1504 Zacuto wrote a history of the Jewish people called “Sefer Yuhasin” in addition to astronomic works. Like his astronomical work, the “Sefer Yuhasin” was well received in many countries. Over the centuries it was reprinted in Poland, the Netherlands, Germany and England.

But the Zacutos’ stay in North Africa would not last long. It wasn’t safe to stay because the region was at threat of Spanish invasion—and everywhere the Spanish went, their anti-Jewish inquisition came too. So Zacuto traveled east to Turkey. It is unclear whether Zacuto remained in Turkey or made it to Jerusalem, but he is believed to have died in either 1515 or 1520.

In any event, we know that Zacuto died far from his hometown of Salamanca. And thanks to his pioneering work, countless other Europeans had for quite different reasons been able to journey thousands of miles from their homes. Abraham Zacuto was a man who contributed as greatly to Europe’s age of exploration as he suffered from its age of intolerance.

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