| From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 1255-1256 |
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Courtesy of 
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Zacut: Abraham ben
Samuel Zacut
Cirilo Flórez Miguel
Born Salamanca,
(Spain), probably 1452
Died Damascus, (Syria),
probably 1515
Abraham
Zacut was an important Jewish astronomer who contributed to observational
astronomy, astronomical tables, and our historical knowledge of astronomy
in Spain. Zacut came from a family originally from France; however, the evidence
indicates that he was born in Salamanca, and spent his early years there as
a pupil of Isaac Aboab, from whom he received the extensive knowledge that
would later make him famous. Although professionally a doctor, Zacut's fame
came from his works in astronomy.
During
his lifetime, Zacut maintained relationships with several notable figures,
including Don Juan de Zúñiga, the last Master of the Order of Alcántara (Maestre
de la Orden de Alcántara), and the Bishop of Salamanca, Gonzalo de Vivero,
to whom he dedicated his most famous astronomical work. When Bishop Vivero
died in 1480, Zacut lost his protector in Salamanca and moved to the court
of Don Juan de Zúñiga for whom he produced the following works: Tratado
breve de las influencias del cielo (Short treatise on the influence of
the heavens) and De los eclipses del sol y la luna (On solar and lunar
eclipses). We know that Zacut was in Lisbon on 9 June 1493, working for Juan
II of Portugal. It is logical to assume that he moved to this city when the
Jews were expelled from Spain following the order of the Catholic kings in
1492. Zacut also worked for the brother of King Manuel I, who is said to have
sought Zacut's advice for Vasco de Gama's trip around Africa, for which Zacut
gave a favorable opinion. When in 1496 King Don Manuel ordered the Jews expelled
from Portugal, Zacut fled Portugal and moved to Tunisia, where he was welcomed
by a large Jewish colony. He lived in Carthage for several months, giving
lessons in subjects for which his expertise was renowned. He eventually moved
to the Ottoman lands and died, probably in 1515 although a death date of 1522
has also been suggested.
It
is not clear whether or not Zacut taught at the University of Salamanca. However,
he was in contact with and influenced some of the professors of astrology
there. For example, Juan de Salaya, who was a professor of astrology from
1464 to 1469, translated Zacut's work titled La Compilación Magna (ha‐Hibbur
ha‐gadol or The magnus compilation) from Hebrew into Spanish. The
Latin translation, known as Almanach Perpetuum, was made by José Vizinho
and first published in Leira in 1496. It became essential for the development
of Spanish and Portuguese navigation at the end of the 15th century. The Spanish
translation made Zacut famous due to its influence on his contemporaries.
La
Compilación Magna was commissioned by Zacut's protector,
Gonzalo de Vivero. Indeed the bishop left instructions regarding Zacut in
his will as follows:
…to
deliver to the Jew Abraham, astrologist, five hundred maravedises and ten
measures of grain, and instructed that certain works which were in Romance,
written by the mentioned Jew, should all be published in a volume together
with his other books in his [i. e. the bishop's] church, because it
is worthy to understand the tables made by the mentioned Jew.
This
volume could be Incunable 176, presently kept at the Salamanca University
Library, which contains the Spanish translation of La Compilación Magna
that was dictated by Zacut to the translator Juan de Salaya.
La Compilación Magna
is a collection of astronomical tables with rules (canons) that served several
purposes. The tables were calculated for the meridian of Salamanca for the
radix year 1473. The first part of the collection contains the rules
in 19 chapters, a number Zacut uses because he considers it a golden number,
following the indication of Maimonides.
In those chapters he first analyzes the positions of the Moon and the Sun,
their movements, circumstances, and eclipses, and then moves to the astrological
houses and to the ascendant. He also provides the longitudes and latitudes
of the main cities; finally he devotes a chapter to the fixed stars. In the
second part of the canons, Zacut explains the circumstances of the other planets
(Saturn, Jupiter, Mars, Venus, and Mercury) and devotes one chapter to the
Jewish, Christian, Islamic, and Persian calendars. This second part comes
to a close with Chapter 19, where he explains the movements of the seven planets
and of the lunar node (Dragon Head). After the canons, he gives the tables
for the material discussed in these 19 chapters. The structure of the tables
is influenced by Jacob Poel (Bonet Bonjorn), an intermediary who connected
the work of Gersonides and Zacut.
More than 50 manuscripts are known of these tables, of which we should particularly
note MS Sassoon 823 for its detailed “representation” of its catalog of stars.
In addition to mentioning Bonet Bonjorn, whom the translator Salaya refers
to by his Hebrew name Jacob Poel (Po ‘el meaning “the artisan”), Zacut mentions
the Jewish scholar Yehuda ben Aser. There are also references to the tables
and calendar of King Alfonso X.
The
canons of the Almanach perpetuum also exist in another Spanish version
that was made by the same José Vizinho who made the Latin translation. A copy
of this Spanish version is kept in an incunabulum of the Colombin Library
of Seville's Cathedral. It consists of 23 chapters dealing with the ascendants
of the 12 houses, explanations of the positions of the Sun and the Moon and
their eclipses, the places and movements of the planets, and a reference in
the last chapter to an “animodar.”
Zacut's
empirical interests are indicated by his observation in 1474 of the Moon covering
the star of the spike in Virgo's hand, when this constellation was approximately
in the middle of the sky. Other astronomical observations attributed to him
are an occultation of Venus by the Moon in July 1476, and a total solar eclipse
in June 1478.
Selected References
Cantera Burgos, F. (1931). “Notas para la historia de la
astronomía en la España medieval: El judio salmantino Abraham Zacut.” Revista
de la Academia de Ciencias Exactas, Físicas y Naturales de Madrid 27:
63–98.
Chabás, José and Bernard R. Goldstein (2000). Astronomy in
the Iberian Peninsula: Abraham Zacut and the Transition from Manuscript to
Print. Philadelphia: American Philosophical Society.
Flórez,
Cirilo et al. (1989). La ciencia del cielo. Salamanca:
CAJA DE AHORROS.
Romano, David (1992).
La ciencia hispanojudía. Madrid: Mapfre.
Swerdlow,
Noel M. (1977). “A Summary of the Derivation of the Parameters in the Commentariolus
from the Alfonsine Tables with an Appendix on the Length of the Tropical Year
in Abraham Zacuto's Almanach Perpetuum.” Centaurus 21: 201–213.