His life is surrounded by legend as befits a Judaeo-Iberian sage, and it is quite difficult for us to separate the hard facts from the embellishments. Thus Zacuto stood at the gate of the great breakthrough of European civilisation: discovery of America, of the Cape of Good Hope, of the seaway to India. He was born and brought up in Salamanca, in Castile though the Portuguese dispute it and claim he and his family are from Evora in Portugal. However, he was usually referred to as the Sage of Salamanca, a city of the great University that kept its place of honour next to Oxford and Sorbonne. In , at age of 20, the young Zacuto began his work on his famed solar declination tables, called Ha-Hibur ha-Gadol or Almanach perpetuum coelestium motium Perpetual Almanac of the Heavenly Bodies , essential for the calculation of geographical coordinates.
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The crater Zagut on the Moon is named after him. Background Zacuto was born in Salamanca, Spain in 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. 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.
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 , Zacuto took refuge in Portugal, where he served as court astronomer to the king, Joao II. 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.
Zacuto also instructed the sailors in the use of his improved astrolabe. In , 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.
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 he was in Jerusalem, where he wrote an almanac in Hebrew and in 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. 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.
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.
Rabbi Abraham Zacuto
The crater Zagut on the Moon is named after him. Background Zacuto was born in Salamanca, Spain in 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.
Zacuto set out the data in a simple "almanac" format, with the positions of a planet easily interpolated between entries, making it quite easy to use. Prior to the Almanach, navigators seeking to determine their position in the high seas had to correct for "compass error" the deviation of the magnetic north from the true north by recourse to the quadrant and the Pole Star. But this proved less useful as they approached the equator and the Pole Star began to disappear into the horizon. As the quadrant could not be used to look directly at the sun, Portuguese navigators began using the astrolabe on board an old land-based instrument to measure the height of the sun indirectly. Prior to that, Zacuto had again improved on the existing astronomical tables, mostly those prepared under King Alphonso X of Castille. The story is that on one of his voyages, when attacked by the natives, Columbus noted that Zacuto had predicted an eclipse for that day, and used this information to threaten the natives and convince them that he could extinguish the Sun and Moon and deprive them of all light. This work became important for the contemporary explorers.