Abraham Zacuto was a Sephardi Jewish astronomer, astrologer, mathematician, rabbi and historian who served as Royal Astronomer in the 15th century to King John II of Portugal. The crater Zagut on the Moon is named after him.
Background
Zacuto was born in Salamanca, Spain in 1452. He may have studied and taught astronomy at the University of Salamanca. He later was for a time teacher of astronomy at the universities of Zaragoza and then Cartagena. He was versed in Jewish Law, and was rabbi of his community.
Education
With the general expulsion of the Jews from Spain in 1492, Zacuto took refuge in Lisbon, Portugal. Already famous in academic circles, he was invited to court and nominated Royal Astronomer and Historian by King John II of Portugal, a position which he held until the early reign of Manuel I.
Career
Zacuto remained at the bishop’s court until the bishop died in 1480, leaving instructions in his will to bind all Zacuto’s writings in a single volume to be deposited in the cathedral library. Zacuto then found a new patron in the person of the grand master of the order of the knights of Alcantara, moving to Gata (Caceres province). Here he wrote works on the influence of the stars and on eclipses of the sun and moon.
When the Jews of Spain were expelled from the country in 1492, Zacuto took refuge in Portugal, where he served as court astronomer to the king, Joao II. and to his successor, Manuel IV, writing quadrennial .ables of solar declination. Zacuto played a major role in preparing Vasco da Gama for his historic voyage to India. The king consulted Zacuto on the position of the stars and Zacuto forecast that the expedition would succeed and that much of India would fall under Portuguese rule. Vasco da Gama met with Zacuto before set¬ting out and received from him the astronomical tables and charts that Zacuto had prepared for the voyage. Zacuto also instructed the sailors in the use of his improved astrolabe.
In 1497, the king of Portugal ruled that all Jews had to convert to Christianity and Zacuto had once again to flee — this time to North Africa. Along the way he was twice taken prisoner, but after a hazardous journey reached Tunis. There he wrote Sefer Yuhasin (“Book of Genealogies”), a lucid account of the history of Jewish tradition with detailed information on the rabbis of the Mishnah and Talmud. The main section covers the period from Ezra to the final redaction of the Talmud but Zacuto then decided to continue the history down to his own times and append an outline ot the history of the world since creation. The book contains considerable information on the individual scholars.
Little is known of his later years. In 1513 he was in Jerusalem, where he wrote an almanac in Hebrew and in 1515 he was in Damascus.
For another twenty years, all solar navigation tables in Portugal were based on his reckonings and made a great contribution to the great Spanish and Portuguese voyages of discovery. Columbus used Zacuto’s tables and it was reported that on one occasion they saved him from death. In the knowledge that Zacuto had shown the imminence of an eclipse, Columbus told natives who were threatening him that he would take the light from them. (The story was later utilized by Mark Twain in A Connecticut Yankee at the Court of King Arthur.) Among his astronomic achievements were the production of the first astrolabe of copper (previously they had been made of wood), increased precision in reckoning the position of the sun, and improved tables (which he wrote in Spanish and Hebrew) to determine latitudes and work out the dates of eclipses.