Mortimer and Raymond Sackler Institute of Advanced Studies
Tel Aviv University, Israel
1. Greeks and Hebrews: two intertwining intellectual progressions
In very broad lines, Western culture is the outcome of two independent
intellectual progressions: Greek philosophy and science, centered on a
rational understanding of the world
With the destruction of the Second Temple (70 AD), the Jewish cult and rites centre on learning much more than before. Judaism, as remodeled for a countryless nation by Yokhanan Ben Zakkay (Ist Century AD) became a study-oriented religion. Note that 1000 years later, in medieval Europe, all male Jews were literate, at a time when in most of Europe, only churchmen could read.
Intellectual evolution is conveyed by teachers and transmitted to their students. Jewish centres of study moved from Israel, where the Mishnah (300 BC - 200 AD) and "Jerusalem Talmud" (250 - 500 AD), i.e. the Proceedings of the Sanhedrin and Academies, were collected and edited, to Babylon (present Iraq) where the larger and more comprehensive "Babylonian Talmud" (200 - 500 AD) was composed, in the three great universities of Surah, Pumbadita and Nehardea. Creative work continued in these institutions, under the "Geonim" (Heads of Academies) until the Xth Century. Around that period, new schools were started, first in Kairouan (Tunisia) and then in Eastern France and the Rhineland ("the Wise of Lothar" in Jewish lore) where a new tradition of Biblical exegesis and of legislation was to grow, that of Rashi (R. Shlomo Itzhaki of Troyes), his grandson R. Tam and the "Tosaftists" (from the Hebrew word for "authors" of appendices).
And yet the greatest teacher of ethical philosophy was Rabbi Moshe Ben
Maimon, better known as Maimonides (1135 - 1204). Born in Cordoba he grew
up as a Moslem marrano (i.e. forced convert, having to hide his
Jewishness) under the intolerant Almoravides. Only when he reached Egypt
and settled there, living under the liberal Fatimids, could he openly appear
and teach as a Jew - even while serving as physician to the Caliph.
The progress of Greek science came to a standstill around the end of the first Century AD. My own conjecture  is that it was caused by the success and enthusiasm on the ethical-religious side. The size of the learned and intellectual class within the Roman Empire was very limited; the total teacher-student population in the 10-15 centers of study active around 100 AD must have amounted to a few hundred souls. All of a sudden, Christianity burst upon the scene. New moral truths, new hopes centering on Salvation, inspiring ideas about human freedom - all of this destroyed the delicate web of scientific teaching and research in natural science. Supposedly, the end of the world was near - who then would be interested in evaluating the distance to the Sun?
2. How science got to Spain
In 529 AD, the School of Athens was all that remained of Greek science, a pale flicker, trying mainly to preserve past intellectual achievements. The orthodox churchmen advising the Byzantine emperor Justinian and his wife Theodora felt that even this minute activity could become a danger to the Faith. They prevailed upon the emperor and he ordered the School of Athens to be closed.
This might have become the burial of Greek science (and could have retarded the end of the Middle Ages by another thousand years...) except for Khushru ("Chosroes I") Anushirvan ("Beloved of the Heavens"), Emperor of Sassanid Persia. He was interested in philosophy, which had already trickled into Persia, brought in by Nestorian refugees. That sect and the Monophysites had incorporated many Aristotelian teachings, which added one more good reason for their expulsion by the Orthodox Church. When in that year - and after a prolonged war - a ten-year truce was negotiated between Persia and Byzantium, Khushru instructed his ambassadors to ask for the teachers of the School of Athens to be transferred to Persian territory. Justinian thought it a good idea and good riddance and Damascius, Head of the School, with six teachers, moved to Babylonia. They established their new school not far from the Jewish Academies. By the time of the Arab conquest, the exiled school had grown new roots and branches in the Middle East and Persia. The intellectual climate improved after the first militant wave of Islam and its intolerance. The next generation of Moslem rulers became interested in knowledge, encouraging study and research, sometime in spite of strong resistance by the Moslem religious spiritual leadership. Note that one well-known alumnus of the Naishapur branch of the imported school of philosophy is the poet Omar Khayyam, who was also an astronomer and mathematician, credited with working out a method for solving the factorizable cubic equations.
Another branch of that school was activated in the Caliph's palace in
820 AD ("Beit al Hikmeh", i.e. House of Wisdom) by the Abbassid Al Ma'mun,
son and successor of Harun al-Rashid
The new climate, encouraging learning, fitted very much with Jewish culture and traditions. Already in the first Century AD, contact with Greek philosophy had brought about a cross-fertilization, especially in Alexandria, where a large Jewish community lived next door to one of the more active centers of Greek learning. The Jewish philosopher Philo of Alexandria (30 BC - 45 AD) tried to identify the overlap between Greek ethics and Hebrew scripture at the philosophical level.
There had also been a beginning of activities in Israel relating to
natural science. Since the Babylonian captivity (597 - 538 BC) an interest
in Astronomy had developed
It was also in the Xth Century in Babylon, under the Abbassids, that R. Sa'adiah Gaon (882-942), Head of the Academy at Sura, made a new start from the point of view of Jewish scholarship. For the first time, Jewish learning embraced philosophy per se, displaying an interest in the rational understanding of nature, borrowing it from the Greeks. From that time on, and especially in the cultural crucible of medieval Spain and under the relatively tolerant regimes of the Popes in Avignon and of the enlightened Kings of Provence - the greatest Jewish thinkers discuss science, parallely to their interest in ethical and ritual issues. For Maimonides, it is mostly Medicine, some "theoretical" (Aristotelian) Physics and Astronomy, plus the struggle against Astrology - a personal crusade, exceptional in the Middle Ages, considering that four hundred years later, Johannes Kepler (1571-1630) was having qualms arising from his involvement in the production of horoscopes for the emperor...
With the transfer of the centres of learning into Umayyad Spain, this country - the Hebrew "Sefarad" - became the scene of the rediscovery of Greek science, followed by first hesitant steps attempting to go beyond. The centers of learning rose and decayed, according to the various degrees of tolerance and openness of the local dynasties, whether Moslem or Christian, the Jews sometimes enjoying the advantage of being able to move between the two regions - and on other occasions having to do it forcibly. In the IX - XIth Century, it was under the Umayyads in the South that the ball started rolling. There was also a very brief return of the enlightment under the Almohades, during the reigns of Yusuf (1163 - 1184) and his successor Ya'kub Al-Mansur - until 1195, when it was all destroyed by a fanatic reaction. In the XIIIth Century, King Alphonso X of Castille (1252-1284) developed the University of Salamanca as a centre of research in the sciences, especially Astronomy.
3. The Jewish astronomers in Spain and Provence
Abraham bar Hiyya of Barcelona (d. 1136)  is the first important Jewish astronomer in Spain. His books "The Shape of the Earth", "Calculation of the Courses of the Stars" and "Book of Intercalation" (all in Hebrew, later translated) reproduce the Greek results, sometimes with new proofs and improved accuracy. He also issued a set of astronomical tables which were much in use later on.
Our map of the Moon, established by the International Astronomical Union at the beginning of the XXth century, carries the names of three great Jewish medieval astronomers, two in Spain (Ibn Ezra and Zacuto), one beyond the Pyrenees (Levi b. Gershon). Abraham Ibn Ezra (1089-1164) of Tudela in Navarre , was a wandering scholar who also issued astronomical tables and wrote treatises on mathematics and intercalation. He travelled extensively, reaching Jerusalem in his old age.
The Alphonsine Tables (1252 - 1256) were computed and edited by a large
number of scholars, led by R. Isaac Ibn Sa'id ("R. Saz")
and Judah b. Moshe Cohen, two Jewish astronomers in Toledo.
But the most original and perhaps the greatest of Jewish Medieval astronomers
was Levi b. Gershon ("Gersonides") in Provence .
He invented "Jacob's Staff"
an instrument for the measurement of angular separations,
which remained in use in navigation up to the XVIIIth Century.
He wrote textbooks on Astronomy. He is the only astronomer before
modern times to have estimated correctly stellar distances.
In the same context, I consider Gersonides' observational refutation of
Ptolemy's model as one of the most important insights in the history of
science, generally missed in telling the story of the transition from
epicyclic corrections to the geocentric model to Copernicus' heliocentric
model. Reviewing Ptolemy's model with its epicycles
Gersonides' experimental intuition was excellent. In one case he observed the angular distance between two fixed stars twice within one year and found slightly different results; he ascribed the difference to atmospheric refraction. This was later strongly criticized by George of Trebizond (1395 - 1472), an astronomer working in Italy. George regarded this result as a punishment for not believing Ptolemy's figures and trying to do better "but Leo (Levi, YN) ... descended to inept demonstrations, trying to save the appearances ... seeking glory most basely by false and deceitful detraction of divine men." Note that this same result of Gersonides was praised by Giovanni Pico della Mirandolla (d. 1494) ... Pico could read Hebrew (a very useful language for astronomers at that time) but also had a translation by the Jewish astronomer (~ 1435) Mordecai Finzi of Mantua ("Angelo") who also translated the Oxford Batecombe tables for 1348.
Gersonides also wrote a treatise in Astrology. Ironically this posthumous work became famous, having predicted a catastrophe, which was identified with the Black Death.
In Cosmology, Gersonides conceived the idea of ongoing continuous creation, which was revived as the Steady-State theory in 1948 by Bondi, Gold and Hoyle - to be reburied in 1965 with the discovery of the Background Radiation, the residual remains of the flash of the Big Bang, 15 billion years ago. The theory has, however, recently been revived, in the context of "Inflationary Cosmology"  yet on a grander scale: the Universe as a whole is infinitely larger than our Observable Universe. There could thus have been (and there most probably were) other Big Bangs, before "ours","elsewhere". Gersonides' ideas are here again.
Hasdai Crescas (d. 1412), originally of Barcelona, was the Rabbi of
Saragossa, working for King John I of Aragon. Crescas wrote severe critics
of Aristotle's physics. He was extensively quoted by Giovanni Pico della
Mirandola, through whose writings his influence reached Galileo, Giordano
Bruno and Spinoza. Crescas may thus have greatly contributed to the
demolition of Aristotelian "authority", a crucial factor in the rise of modern
science . This was in direct opposition to the influence of the great
Arab philosopher and astronomer "Averroes" (Ibn Rushd) of Cordoba
(1126-1198), who mainly propagated Aristotle's theses
The last Jewish astronomer in Spain to have a large crater on the Moon named after him is Abraham Zacuto (1452-1515), who studied at the University of Salamanca and later became a Professor of Astronomy . Gonzalo de Vivero, bishop of Salamanca was his patron and admirer. After the Bishop's death in 1480, Zacuto continued his astronomical research in Gata, in the province of Caceres, in the service of Don Juan de Zuniga, Grand Master of the Order of the Knights of Alcantara. There he wrote a book on eclipses, calculating those of coming years. The book was written in Hebrew, but it was almost immediately translated into Spanish. In 1492, he left Spain at the expulsion order and moved to Portugal, where he became Royal Astronomer to John II and Manuel I. There he was a kind of Werner von Braun in the "NASA"-like institution created half a century earlier by Prince Henry the Navigator. Before setting on the voyage to India in 1496, Vasco da Gama and his crew underwent a thorough briefing and preparation by Zacuto, in addition to learning to use the new instruments which he had developed for their trip (including a special metallic astrolabe). Prior to that, Zacuto had again improved on the existing astronomical tables, mostly those prepared under King Alphonso X of Castille. Already Columbus had used Zacuto's tables. 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. Zacuto's work thus saved the Admiral's life and that of his crew.
In 1497, Portugal followed Castille and Aragon and expelled the Jews. Zacuto moved first to Tunis, later to Jerusalem (1513). The Jewish contribution to Iberian culture came to an abrupt end.
And yet it was in medieval Spain that Jewish learning acquired a new dimension: rather than being satisfied with the quest for humanistic ideals (it is not surprising that there have been many Jewish thinkers in the evolution of Socialism, for instance ). In line with the original evolution of the Judeo-Christian ethic, Jewish thinkers have joined the scientific quest for a rational understanding of nature, the line started by the Greeks. Although individuals such as Spinoza continued in the Netherlands, the expulsion from Spain and then the massacres in Eastern Europe in the XVIIth Century, caused a slow-down. With the emancipation that followed the French revolution, however, we observe a strong return to the sciences, starting with Jacobi and culminating with Einstein (who also has a crater named after him on the Moon...). About one third of Nobel Laureates in Physics and Chemistry nowadays are Jewish. As far as craters on the Moon are relevant, even modern Israel has already produced a physicist, G. Racah (1909-1965), who has contributed greatly to Atomic Spectroscopy and now has a crater named after him, on the newly explored "dark side" of the Moon. Israel has the highest density of scientists in the world. This transformation, this interest in a rational understanding of the world - while the quest for justice and ethics was changing from a religious progression to an ideological one - this takeover of the Greek line, this is one of the gifts that the Jews have carried over from the "Golden Age" of Sefarad.
|History of Jewish Astronomy|
Astronomy in Israel:|
From Og's Circle to the Wise Observatory
|Astronomy in Sefarad (Spain)|