Abraham Zacuto (, ; 12 August 1452 – ) was a Castilian astronomer, astrologer, mathematician, rabbi and historian who served as Royal Astronomer to King John II of Portugal. His astrolabe of copper, his astronomical tables and maritime charts played an important role in the Spanish and Portuguese navigation capability. They were used by Vasco Da Gama and Christopher Columbus. Life Zacuto was born in Salamanca, Castile in 1452. He may have studied and taught astronomy at the University of Salamanca. He later taught astronomy at the universities of Zaragoza and then Carthage. He was well versed in Jewish Law, and was the rabbi of his community. With the Catholic Monarchs of Spain issuing the 1492 Alhambra Decree ordering the expulsion of the Jews, 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. He was consulted by the king on the possibility of a sea route to India, a project which he supported and encouraged. Zacuto was one of the few who managed to flee Portugal during the forced conversions and prohibitions of departure that the Portuguese king Manuel I enacted to keep the Jews in Portugal as nominal Christians for foreign policy reasons (see persecution of Jews and Muslims by Manuel I of Portugal). Zacuto first fled to Tunis and later moved to Jerusalem. He probably died in 1515 in Jerusalem; however, other reports indicate his final home was the Jewish community in Damascus and his death occurred in 1520. However, in a similar vein to other giants of the Jewish faith, such as Saadia Gaon, Maimonides and the Vilna Gaon, he followed the Jewish custom (believed to have begun in the Babylonian captivity) of being buried as close to Jerusalem as possible. Zacuto had announced his wish to make his death pilgrimage at a Passover gathering. Work Ha-ḥibbur ha-gadol Abraham Zacuto developed a new type of astrolabe, specialised for practical determination of latitude while at sea, in contrast to earlier multi-purpose devices intended for use ashore. Zacuto's principal claim to fame is the great astronomical treatise, written in Hebrew while he was in Salamanca, with the title Ha-ḥibbur ha-gadol ("The Great Book"). It was begun around 1470 and completed in 1478. It was composed of 65 detailed