Abraham Zacut (1450-1522)

Abraham bar Samuel Abraham Zacut, known in Portugal as Abraão Zacuto, is thought to have been born in Salamanca in the mid-fifteenth century, where it is believed that he taught astrology and astronomy – as is known, at the time these two subjects were intermixed. There are no certainties about his activity in Salamanca, only unconfirmed references to the fact that he studied and lectured at the University of Salamanca. He had to seek refuge in Lisbon following the promulgation of a decree by the catholic monarchs, king Fernando and queen Isabel, rulers of Castela and Aragon, who forced Jews to convert to Christianity or to exile. There is news that he was already in Portugal in June 1493, at the service of king João II. He lived for only six years in Portugal as in 1496, king D. Manuel followed suit, issuing a decree that expelled from the country all Jews who refused to convert to Catholicism through baptism. Zacuto sought refuge in Tunes, in the North of Africa, having then moved on to Turkey. He died in the city of Damascus sometime after 1522.

(click on the picture above for an enlarged version)

First page of the tables in Abraham Zacut’s Almanach Perpetuum from a copy which exists in the National Library. The tables occupy a total of 300 pages. The work was published in Leiria in 1496 by the Jew Abraão d'Ortas. As far as is known, this was one of the first books to have been printed in Portugal and the second to have been printed in Latin. According to the most recent historiography, the first books to be printed in our country were the Pentateuto, printed in Hebrew characters in Faro in 1487, and the Tratado de Confissom, the first Portuguese book, printed in Chaves in 1489.

Abraham Zacut was an astrologist and astronomer of renowned reputation even before moving to Portugal. Here he made important contributions to the development of nautical science, creating the first tables or quadrennial tables of the sun for navigation, in his Almanach Perpetuum. According to Luciano Pereira da Silva, all the quadrennial solar tables calculated in Portugal were deduced from Zacut’s Almanach, until the publication of Pedro Nunes’ sun tables. This work was re-edited several times throughout the fifteenth and sixteenth centuries.

Written in Hebrew, under the title Hajibur Hagadol, the Almanach Perpetuum Celestium Motuum is made up of a set of astronomical tables of various types and for different purposes, preceded by explanations or canons on their use. The Almanach was prepared for the root year of 1473 (that is its time period, as it is said), which means that the numbers written in its tables are calculated for that year, or for specific periods of several years starting in that year. It was necessary to make corrections when one wished to know the values of the elements in the tables for any year subsequent to the periods set in the tables. The Almanach Perpetuum is thought to have been written between 1473 and 1478, the date referred to by its author in his introduction. The book was re-edited in Leiria in 1496, having been translated from Hebrew to Latin and from Latin to Castilian by Mestre José Vizinho, doctor of the court of D. João II and astronomer, who was a disciple of the author.

The Almanach reproduces the movement of the celestial bodies with reference to certain astronomical coordinates. It foresees the moments and coordinates of celestial occurrences, the so-called ephemeredes. In this way, the tables presented in the Almanach made it possible to determine the position of the celestial bodies, to determine the exact moment of eclipses and to perform various types of astronomical and astrological calculations. As Crespo states, “The curiosity in determining the position of the heavenly bodies in the celestial sphere in terms of time was not merely scientific. It was essentially used for astrological purposes, using the word in the sense of predicting occurrences and the behaviour of people in relation to the celestial bodies. It was also used for medicinal, agronomical, meteorological, religious and other purposes, in many cases with the tables being organised to serve these purposes. The book does not, however, deal with these issues; it merely provides astronomical data which were subsequently used to make speculations on the referred sciences”. (Crespo, p. 123)

Using the first four solar tables of the Almanach as a basis, it was possible to accurately determine the position of the sun on the ecliptic. Based on this figure and using a fifth table, it was possible to obtain the value of the declination of the sun, an astronomical parameter necessary to calculate the latitude of the place of observation when the meridian height of the sun was used. These tables could be used directly for the years 1473 and 1476. For subsequent years, it was necessary to make some calculations, simplified by the assistance of another table which Zacut included in his Almanach. The degree of precision offered by these tables was such that they were used as the basis of several other tables designed for mariners and which contained the results of the calculations required by Zacut’s tables.

Besides this work, without a doubt the most important written by him, he also published a chronicle titled Livro das Genealogias, which includes autobiographical data and two astrological treaties, Juízos astrológicos and Tratado de las Ynfluencias del cielo, annexed to which is a text with the title De los eclipses del Sol y de la Luna. The Tratado de las Ynfluencias del cielo Zacuto, which Luís de Albuquerque classifies as "astrological meteorology", includes a prognosis on a flood in Europe. A prognosis was made by Joannes Stoeffler and Jacob Pflaum for the 4th and 5th of February 1524, which was widely disseminated causing widespread panic and giving rise to a series of texts which refuted the prognosis. In his Tratado de las Ynfluencias del cielo, Zacut predicted a worldwide flood for the year 1503. his prediction did not have a greater impact because it remained as a manuscript and was only made known to a restricted number of people.

Fernando Reis


ALBUQUERQUE, Luís de, "Zacuto, Abraão", in Dicionário de História de Portugal, Porto, Figueirinhas, 1981, Vol. VI.
ALBUQUERQUE, Luís de, "Zacuto, Abraão", in Dicionário de História dos Descobrimentos Portugueses, Lisboa, Círculo de Leitores, 1994, Vol. II.
CANTERA BURGOS, Francisco, Abraham Zacut, Madrid, M. Agilar, s. d. [1935].
CANTERA BURGOS, Francisco, El Judio Salmantino Abraham Zacut, Madrid, C. Bermejo, [1931].
CRESPO, Victor, "Abraão Zacuto e a Ciência Náutica dos Descobrimentos Portugueses", Oceanos, 29, Jan-Mar. 1997, 119-128.
ZACUTO, Abraão, Almanach Perpetuum, Lisboa, Imprensa Nacional-Casa da Moeda, 1986. [introdução de L. de Albuquerque].


Abraham Zacuto
Zacuto - Dicionário Histórico
Judaic Treasures of the Library of Congress: Columbus Sets Sail

© Instituto Camões 2003-2005