Abraham Zacuto (Hebrew: ????? ????, Portuguese: Abraćo ben Samuel Zacuto) (c. 1450 – c. 1510) was a Sephardi Jew astronomer, astrologer, mathematician and historian who served as Royal Astronomer in the 15th century to King John II of Portugal. The Zagut crater on the moon is named after him.

Life

Zacuto was born in Salamanca, Spain circa 1450. He studied astronomy at the University of Salamanca and taught there as well. 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.

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 Joćo II, a position which he held until the early reign of Manuel I. He was consulted by the King on the possibility of a sea route to India, a project which he supported and encouraged. Zacuto would be one of the few who managed to flee Portugal during the forced conversions and prohibitions of departure that Manuel I enacted, in order to keep the Jews in Portugal as nominal Christians for foreign policy reasons (see History of the Jews in Portugal).

He died in the Ottoman Empire, to where he had escaped, ca. 1510.

Work

page from Almanach Perpetuum.

Zacuto perfected the astrolabe, which only then became an instrument of precision, and he was the author of the highly accurate Almanach Perpetuum that were used by ship captains to determine the position of their Portuguese caravels in high seas, through calculations on data acquired with an astrolabe. His contributions were undoubtedly valuable in saving the lives of Portuguese seamen, and allowing them to reach Brazil and India.

While in Spain he wrote an exceptional treatise on astronomy/astrology in Hebrew, with the title Ha-jibbur Ha-gadol. He published in the printing press of Leiria in 1496, property of Abraćo de Ortas the book Biur Luhoth, or in Latin Almanach Perpetuum, which was soon translated into Latin and Spanish. In this book were the astronomical tables (ephemerides) for the years 1497 to 1500, which were instrumental, together with the new astrolabe made of metal and not wood as before, to Vasco da Gama and Pedro Įlvares Cabral in their voyages to India and Brazil respectively.

In 1504, while in Tunisia, he wrote a history of the Jewish people, Sefer Hayuhasin, since the Creation of the World until 1500, and several other astronomical/astrological treatises. The History was greatly respected and was reprinted in Cracow in 1581, at Amsterdam in 1717, and at Königsberg in 1857, while a complete edition was published by Filipowski in London in 1857.

External links

• Short biography of Rabbi Abraham Zacuto
• JewishEncyclopedia
• Freeily available downloadable copy of one of the earlier printings of Sefer HaYuchasin
• A downloadable copy of Sefer haYuchasin printing from the middle 19th century

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