Sunday 10 July 2016


Five hundred years ago, Rabbi Avraham Zacuto[1] was probably one of the most accomplished people of his generation. Born in Spain in 1452, although originally a doctor, he became arguably the greatest astronomer of the era. Astronomy then was as critical to exploration as rocket science is to space travel today. Without his knowledge, guidance and inventions, Christopher Columbus and Vasco da Gama may have failed in their missions.


At the age of 20 he began work on his HaChibur HaGadol or Almanach which calculates geographical coordinates. The Hebrew text was then translated into Spanish. In the introduction to his tables, he wrote that he also intended to write a book on the Sages of the Mishna and Talmud. (We will deal with this work later on in this article.)

After the captains of the sailing vessels were instructed by Rabbi Zacuto, his charts were used to discover America, the Cape of Good Hope and the seaway to India. When Columbus arrived in Spain he met extensively with Rabbi Zacuto who showed him some of the astronomic writings of Ibn Ezra, and also introduced him to Rabbi Don Yitzchal Abravanel.[2]

Zacuto was one of the few who believed in the successful completion of Columbus’ journey. There is a family tradition that Rabbis Zacuto’s son sailed with Columbus, advising on navigation.[3]
A copy of Rabbi Zacuto’s tables with notes by Columbus is extant in the Colombian library in Portugal.

Rabbi Zacuto's Tables

After fleeing Spain, he settled in Portugal where his knowledge of storms and gales made it possible for him to advise Vasco da Gama on a route to India. Rabbi Zacuto told King Manuel that India would soon belong to Portugal.[4] So respected was Rabbi Zacuto, that his tables were among the first printed material in Portugal after the invention of the printing press.[5]

Additionally, he made the first ever copper astrolabe which allowed for extremely accurate readings to determine latitude while at sea for navigational purposes. In the Biur Luchot, another of his works, Rabbi Zacuto revolutionized ocean navigation. Until then, sailors had to correct for compass error (the deviation of magnetic north from true north) by using the quadrant and the Pole star. However on approaching the equator the Pole Star began to disappear behind the horizon. Zacuto’s tables allowed them to use the sun instead. And since the quadrant could not be used to look directly at the sun, Zacuto’s astrolabe became invaluable. 

He also provided the longitudes and latitudes of the main cities of that time. Many of the great astronomers from around the world corresponded with him and sought his opinion.

The 84 km diameter moon crater Zagut is named after Rabbi Zacuto (his Hebrew name was Zechut) in recognition of his contribution to astronomy.[6]


 Rabbi Zacuto was very aware that such contributions to science by a Jew and particularly a rabbi, created an unimaginable kiddush haShem or favourable impression among his non-Jewish peers.
His first publisher wrote in 1566: “All preceding tables of Gentiles were of naught and they broke and discarded all previous tables and adopted his wonderful creation...”[7]

He was acutely aware of the Kiddush haShem his contributions made. He wrote; “When I was in the kingdom of Spain and also in other Christian kingdoms, my books on astronomy appeared which were titled ‘by Rabbi Abraham Zacuto of Salamanca’. And I am permitted to glory in this, as the sages have said, ‘What wisdom is it that made (Jewish) scholars great in the eyes of the nations? It is the calculation of times and signs.’ And I bear witness to Heaven that they praised Israel very much for this.”

Not quite sure what an astrolabe was, I looked it up and too was proud to read; “the first known European metal astrolabe was developed in the 15th century by Rabbi Abraham Zacuto in Lisbon.”[8]

To this day Rabbi Zacuto features in The Oxford Encyclopedia of Maritime History, The Oxford Companion to World Exploration and The Oxford Dictionary of the Renaissance.[9]


Rabbi Zacuto’s teacher was the great mystic Rabbi Abuhav[10] (who designed the famous synagogue by the same name in Safed). After being expelled from Portugal, Rabbi Zacuto fled once again, this time to Tunis[11] where he became acquainted with Rabbi Moshe Alaskar.

It was in Tunis where he wrote the majority of his Sefer haYuchsin (Book of Lineage) which recorded the first 1 500 years of Jewish history. Rabbi Zacuto wrote; “This year (1499) is the thousand-year anniversary of the completion of the Talmud.”[12]

Amazingly he wrote this encyclopaedic work with apparently only one tractate of Talmud (Nezikin) and hardly any other reference books except for those few the exiles brought with them. He was honest enough to admit that he only wrote about; “...the sages of the Mishna and Babylonian Talmud as we have it, excluding the sages of the Baraita, as I do not know them and their dates.” [13]

This is the first systematic record of Talmudic sages, because hitherto there seems not to have been a need to present the Talmudic era in a historic perspective including dates, spiritual and philosophic movements and trends. He felt this was important from a halachic point of view to know who preceded whom, in order to show the oldest opinion - which is usually regarded as most authoritative. It also contains great details about the lives of the Talmudic sages and their families.

The work is of particular relevance to the question of the age of the Zohar. But a crucial section was censored for three hundred years because it contained an account by Rabbi Yitzchak of Akko that that Zohar may only have been written in the 1200’s. The uncensored version was finally published in 1857. Sefer haYuchsin is the only primary source on the age of the Zohar as all other writers simply quote from it in this regard. 

In the 1700’s, for example, Rabbi Yaakov Emden added notes to (the original version of) Sefer haYuchsin, and used it to show that the Zohar was a forgery, in his view, and was not written by Rabbi Shimon bar Yochai. See previous post.

This is how the 1857 uncensored edition records the events:

The first edition appeared in Constantinople in the year 5326

The second edition appeared in Krakow in the year 5340

The third edition appeared in Amsterdam in the year 5476

The first publisher cut the manuscript to pieces

The second publisher abridged the book mercilessly

The third one decimated what the first two left over


The censored Krakow edition of Sefer haYuchsin
Rabbi Moshe Haggis wrote of Sefer haYuchsin“If you wish to quench your thirst and to find the origins and descent of the Sages of the Mishna and 
Talmud and to learn everything about them...keep close to your heart this pleasant book and it will encourage your spirit to study the Oral Torah.”[14]

He had an interesting style of writing. He would often spell a word differently on the same page. He knew his Talmud by heart and he would quote a passage by only referencing one or two words and expect the reader to be equally erudite.

Rabbi Zacuto had a love for Talmud and had also written a supplement to the Sefer Ha’aruch[15], which is a dictionary of Talmudic Aramaic.


We have seen how Rabbi Avraham Zacuto was able to straddle both the secular and Torah world, and became a master of both. In many ways this remarkable ability was common to many of our classical rabbis.

Sadly though, it seems as if this worldview has become dormant in modern times.

What has changed in Judaism today that our rabbis are no longer known for their contribution to technology (or even to humanitarianism)?  How many rabbis work for NASA or for the United Nations? They have incredible minds yet are not generally known outside the four cubits of their local teaching platforms.

The Vilna Gaon summarised it best when he asked (apparently many times); “Compared to the Torah scholars of the past, what are our contemporary scholars doing when it comes to kiddush haShem? In previous generations our scholars made an indelible imprint in the hearts of non-Jews who came to respect religious Jews for their secular knowledge.”[16]

 One cannot help but wonder if there ever be another rabbi who gets crater named after him?

The First English Translation of Sefer haYuchsin (Translated by Israel Shamir).
The Esoteric Codex: Medieval Astrologers, by Hipolito Buchmann.
The Jewish Quaterly Review,Zacuto’s Astronomical Activity, by Raphael Levy.
Zacuto Foundation.

[1] His Hebrew name appears to have been Zechut, and he is also known by the abbreviation Raz (Rabbi Avraham Zacuto).
[2] Zacuto also arranged for Columbus to have an audience with the King and Queen. 
It would be fascinating to know why, in the 12 surviving letters that Columbus wrote to his son Diego, the letters bet and hay appear in the upper left corners. Furthermore, Luis de Torres (or Yosef Levi haIvri) the first to sight land, was hired as an interpreter, because it was believed that they would encounter remnants of the lost tribes of Israel.
[3] When Columbus was marooned in Jamaica, he was threatened by the natives. That night, according to Zacuto’s charts, was to be a lunar eclipse and Columbus used this information to save his crew when he proclaimed that he would destroy the moon.
[4] Correa, Lendas da India.
[5] It has been said that Zacuto helped two countries become the richest and most powerful on earth – yet, sadly he was expelled from both.
[6] There is another moon crater in close proximity to Zagut, also named after a rabbi, entitled ‘Rabbi Levy’, named after Gersonides.
[7] From the Introduction to Sefer haYuchsin.
[8] Although of Spanish origin, the Portuguese claimed him as one of theirs. And fleeing persecution, Zacuto did later settle in Portugal where he made contact with Vasco da Gama. He established a synagogue in Tomar which still exists today.
[9] See Oxford Reference.
[10] Author of Menorat haMaor. Zacuto seems to have had a rare combination of Mysticism and Philosophy in addition to being a master Talmudist.
[11] He refers to himself (proudly) as; “A resident of Tunisia in the Land of Africa”.
[12] Sefer haYuchsin p 204a.
[13] From his introduction to Sefer haYuchsin.
[14] Mishnat Chachamim 652
[15] By Rabbi Natan ben Yechiel (1035-1106). Rashi (1040-1105) is said to have referenced the Sefer haAruch.
[16] Kol Hator 5,2.

1 comment:

  1. Ibn Ezra also has a crater on the moon named after him. Actually 4 of the 300 craters on the moon are named after Jews; 5 if you count Zerah Yisroel 19th century astronomer, Caroline Heschel. Yeah, she was a girl, too.