August 12, 1452, is the birthdate of the Spanish-Jewish astronomer and historian Abraham Zacuto, who advised the court of Portuguese King John (or Juan) II, and whose state-of-the-art navigation innovations were used by both Christopher Columbus and Vasco da Gama.
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Abraham ben Samuel Zacuto was born in Salamanca, Castile, to a family that had come to Iberia from France early in the 14th century. He acquired his Jewish learning from both his father, Samuel Zacuto, and with the great rabbinical scholar Isaac Aboab II, and studied astronomy and astrology at the University of Salamanca.
Prior to the expulsion of the Jews from Spain, Zacuto worked under the patronage of the bishop of Salamanca, Gonzalo de Vivero and, after his death, for Don Juan de Zuniga, grand master of the Order of Knights of Alcántara. In these years, he wrote, successively, “Hahibbur Hagadol” (“The Great Work,” finished in 1478), an up-to-date astronomical treatise, in Hebrew, that charted the changing positions of the sun, moon and planets; and his “Brief Treatise on the Influences of the Heavens,” in 1486.
In 1492, Zacuto left Spain for Lisbon, where he became royal astronomer to King John II, who ruled from 1481-1495. He continued in that position under John’s successor, Manuel I, but when the latter compelled the Jews of his kingdom to convert to Christianity, in 1497 Zacuto escaped for North Africa.
It was that same year that the explorer Da Gama set off from Portugal to seek a sea route to India. King John had consulted with Zacuto before giving his imprimatur to the journey, and Da Gama and his crew also had training with Zacuto on the use of the copper astrolabe he had developed for use in determining one’s latitude while at sea, and his astronomical charts.
Zacuto predicted that Da Gama would succeed in his mission to find a sea route to India (as he did), and that Portugal would gain control of large parts of the subcontinent.
Columbus is also said to have relied on – in fact, had his life saved by – Zacuto’s charts that predicted future lunar and solar eclipses. When he and his men were threatened with death by natives they encountered on one of their stops in the New World, Columbus, knowing that a lunar eclipse was about to take place, told his captors that he would make the sky go dark, and so scared them that he was released.
Zacuto and his son Samuel were taken prisoner twice in North Africa before settling in Tunis. There, he finished work on his great historical work, “Sefer Hayuhasin,” a chronological record of the Jewish sages who composed the Talmud, and their successors.
It is believed that Abraham Zacuto died in Jerusalem, probably in 1515, although there is some evidence that he ended his life in Damascus, five years later.