He was a key figure in the Age of Discovery as his studies revolutionized ocean navigation
During the Middle Ages, religion permeated all aspects of society and the different communities learned to live together and share the same spaces. It was not an easy task, especially for the Jewish communities that alternated permissive moments with other intolerant and repressive ones.
This situation was not an obstacle for them to bequeath us an enormous cultural suitcase. In some pajamas, science, literature, drama, philosophy, theology… experienced a true revolution.
In the Middle Ages, astronomers offered, as a general rule, a product based on astrological prediction, which did not prevent them from being used by some monarchs to make important political decisions.
In the middle of the 15th century, Abraham Zacuto (1452-1515), a distinguished astronomer and mathematician who was called to revolutionize ocean navigation, was born in the Jewish quarter of Salamanca.
He belonged to a family of French exiles, his grandfather fled the anti-Semitic laws dictated by the Frankish king Felipe el Hermoso, and in 1306, after crossing the Pyrenees, he settled on the Castilian plateau.
Abraham’s father worked as a rabbi on the banks of the Tormes, which allowed him to enjoy a privileged education and develop his scientific interests. Around 1475 he published ‘Composicion Magna’, a complex work in which astronomical tables appear, calculated for the meridian of Salamanca, which corrected the errors of the ‘Tablas alfonsinas’.
The interest of Jewish scientists in astronomy was due to the fact that it allowed them to accurately determine the moment in which the new moon appeared, which marked the beginning of the Sabbath and the beginning of the new year.
A scientist at the Portuguese court
Zacuto was a strong defender of the role played by astronomy in preserving health, arguing that the signs of the zodiac influenced each of the parts of the body and that their knowledge helped physicists to determine the prognosis of some diseases.
In 1492, with the expulsion of the Jews, Zacuto emigrated to Portugal, where King John II appointed him royal astronomer and court historian. His successor to the throne, Manuel I, asked him for advice on an expedition with which he planned to reach India by circumventing the southern cone of the African continent.
Apparently, the Hebrews issued a favorable opinion while emphasizing that the stars indicated that the success of the company depended on the two brothers leading the expedition. It seems that this detail was decisive for Vasco de Gama, the captain of the Navy, to be chosen since he had a brother.
It is said that Zacuto prepared the maritime and astronomical calculations that made the expedition possible and that, in addition, he trained the crew in the use of an astrolabe of his creation, which allowed the geographical latitude to be determined during navigation.
In 1496 he published a version of the ‘Magna Composition’ under the title ‘Perpetual Almanac’ which would enjoy enormous notoriety for more than a century.
The success of the maritime enterprise with the Portuguese flag was not an obstacle so, in 1497, in the context of a new anti-Semitic wave in Lusitanian lands, he had to emigrate to North Africa, from where he would travel to Damascus, the city that finally saw him die.
The saving eclipse
Christopher Columbus knew Zacuto personally and used his maritime tables in the expedition to the Indies. In them, the solar declination was collected – the angle formed by the sun’s rays with the plane of the equator – which allowed the position of the equator to be determined with great precision, without the need to resort to the polar star.
During the last Columbian voyage in February 1504, the fleet was marooned in Jamaica, where the natives refused to provide them with food. Zacuto’s tables predicted a lunar eclipse for February 29. The admiral gathered the caciques of the island and threatened to make the moon disappear if they did not satisfy his needs. Apparently, the lunar eclipse scared the Indians so much that they not only spared the lives of the sailors but provided them with everything they asked for.
