Abraham Zacuto

• 1. Introduction

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  Abraham Zacuto was born in Salamanca on the 12th of August 1452, into a family that had lived on the Iberian peninsula since the expulsion of Jews from France in 1306. He came from a lineage of scholars: his ancestor Abraham Zacuto the first had written the Sepher ha-Mishpotim in 1311, a manuscript now held in the library of the Jewish Theological Seminary in New York. By the time the third Abraham Zacuto reached adulthood, he had mastered astronomy, mathematics, astrology, and Jewish law. He taught at universities, served a king as Royal Astronomer, and produced tables of celestial motion that guided the ships of Vasco da Gama and Christopher Columbus into waters no European had charted. Then the world he had built collapsed around him. He spent the last years of his life as a refugee, moving from city to city, carrying his scholarship with him. How does a man who helped open the age of oceanic discovery end up fleeing the very empires his work made possible? That question is at the heart of Abraham Zacuto's story.

• 2. The Scholar of Salamanca

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  Salamanca was where Zacuto's intellectual life took shape. He may have studied and then taught astronomy at the University of Salamanca, the most prestigious institution in Castile, before later holding posts at the universities of Zaragoza and Carthage. His brother-in-law was the kabbalist Rabbi Abraham ben Eliezer Halevi, and Zacuto himself served as rabbi of his community, fully versed in Jewish law. The great work of this period was Ha-hibur ha-gadol, which translates roughly as "The Great Book." Begun around 1470 and completed in 1478, it was written in Hebrew and consisted of 65 detailed astronomical tables called ephemerides. The tables had their radix set for the year 1473 and their meridian fixed at Salamanca, charting the positions of the Sun, Moon, and five planets. Zacuto based his calculations on the Alfonsine Tables and drew on earlier astronomers, notably those of the fourteenth-century Majorcan school. Rather than presenting data in an impenetrable scholarly format, he arranged the tables in a straightforward almanac style so that the position of a planet could be interpolated easily between entries. In 1481, just three years after the book's completion, Juan de Salaya produced the first Castilian translation.

• 3. Exile and a New Court

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  The Alhambra Decree of 1492, issued by the Catholic Monarchs of Spain, ordered the expulsion of all Jews from the Spanish kingdoms. Zacuto crossed into Portugal and made his way to Lisbon. His reputation had arrived before him. King John II of Portugal invited him to court and nominated him Royal Astronomer and Historian, a position he held into the early reign of Manuel I. The king consulted Zacuto directly on whether a sea route to India was feasible. Zacuto supported the project and encouraged it. His Portuguese disciple Joseph Vizinus, known also as Mestre Jose Vizinho and described as the much-valued physician and advisor of John II, translated Ha-hibur ha-gadol into Latin under the title Tabulae tabularum Celestium motuum sive Almanach perpetuum, meaning "Book of Tables on the celestial motions or the Perpetual Almanac." Vizinus also produced a new Castilian translation, and in 1496 Samuel d'Ortas published both in Leiria, Portugal. That Leiria edition was among the first books produced in Portugal using a movable type printing press.

• 4. Navigating Without the North Star

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  Before Zacuto's Almanach perpetuum reached sailors, finding one's position on the open sea depended on the Pole Star and a quadrant. That method worked at northern latitudes, but as Portuguese ships pushed south and the Pole Star sank toward the horizon and finally disappeared below it, navigators were effectively sailing without a fixed reference point. Zacuto's tables addressed the problem directly by supplying the first accurate table of solar declination. With that data, navigators could use the sun in place of the Pole Star. But the quadrant, which required looking directly at the sun, was useless for that purpose. Portuguese sailors began adapting the astrolabe, an older land-based instrument designed to measure the height of celestial objects indirectly. Zacuto himself developed a new type of astrolabe cast in copper, specialised for practical determination of latitude while at sea, as opposed to the earlier multi-purpose models built for use ashore. Together, his tables and the new metal nautical astrolabe gave navigators accurate readings anywhere on earth. Already in 1497, Vasco da Gama used Zacuto's tables and the astrolabe on his maiden voyage to India, and Portuguese ships continued to rely on them to reach destinations as far as Brazil and India in the years that followed.

• 5. Da Gama, Columbus, and an Eclipse

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  Vasco da Gama did not simply take Zacuto's instruments and sail. According to the source, da Gama and his crew underwent a thorough briefing and preparation by Zacuto himself. They learned to use the new instruments before their fleet departed in 1496. A meeting between Zacuto and da Gama at a monastery near Belem beach just before departure was later reported by the chronicler Gaspar Correia. At that meeting, Zacuto reportedly gave da Gama final navigational tips and warned him of the dangers to avoid. That encounter may have left a literary trace: the poet Luis de Camoes, writing his 1572 epic poem Os Lusiadas, included a character called "the Old Man of Restelo," a Cassandra-like figure who appears in Canto IV just before da Gama's departure to warn of the hardships ahead. Some scholars read that figure as Camoes's poetic interpretation of the old Abraham Zacuto. Christopher Columbus had also used Zacuto's tables. A well-known story attaches to one of his later voyages: when Columbus found himself threatened by hostile natives, he consulted Zacuto's tables, noted that an eclipse had been predicted for that day, and threatened to extinguish the Sun and Moon unless the confrontation ended. The eclipse arrived on schedule, and Columbus and his crew were spared.

• 6. Flight and Final Years

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  Manuel I of Portugal, who succeeded John II, had his own reasons for keeping the Jews in Portugal. For foreign policy purposes he wanted them to remain as nominal Christians, and he enacted forced conversions alongside prohibitions on departure. Zacuto was among the few who managed to escape. He fled first to Tunis. There, in 1504, he completed Sefer yuhasin, a history of the Jewish people running from the Creation of the World to the year 1500, alongside several other astronomical and astrological treatises. The history earned wide respect and was reprinted in Cracow in 1581, in Amsterdam in 1717, and in Konigsberg in 1857. A complete uncensored edition was published by Herschell Filipowski in London in 1857. From Tunis, Zacuto eventually made his way to Jerusalem. He had announced at a Passover gathering his wish to make a final death pilgrimage, following the custom, believed to trace back to the Babylonian captivity, of being buried as close to Jerusalem as possible. He probably died in 1515 in Jerusalem, though other reports place his final home in the Jewish community of Damascus and his death in 1520. The small Abraham Zacuto Portuguese Jewish Museum, founded in 1939 in the former Synagogue of Tomar, now carries his name, and the lunar crater Zagut was named in his honor.