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 * - and Hebrew ethics, worrying about the condition of man and his interaction with other men. ** On the Greek side, we note that at the beginning of the first Century AD, Eratosthenes (250 BC) had already computed the diameter of the earth with an error of less than 1/2 %, Hipparchus (150 BC) had evaluated the distance to the Moon with a 1/3 % precision, Hero (100 BC) had invented the steam engine [1]. On the Jewish side, Abraham (1800 BC) had put an end to human sacrifice, Moses (1300 BC) had codified the day of rest, to be applied even to slaves and house animals, Amos (800 BC) had preached social justice and Isaiah (700 BC) had already conceived the idea of universal peace - in a world where war remained the explicit ideal "manly" activity for another thousand years [2]. Note that in this ethical voyage of discovery, Jewish society had evolved "schools" as early as 1000 BC [3], the earliest foundations of what was later to become a learning-oriented culture. In parallel, we have, of course, the Athens Academy ( ~ 500 BC).

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 [4] 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?

---------------------
* Greek culture of course includes Socrates and Plato - and Greek philosophy thus indeed encompasses both ethics and "politics" as well as logic, epistemology and metaphysics, the precursors of science. Nevertheless, the main input in the ethical tradition of western society has been that of the Bible and of Christianity.

** The Hebrew cultural contribution did include the study of astronomy, for the purposes of the Jewish Calendar, a science-oriented pursuit. Yet here again, this was a relatively modest contribution to the birth of science, as compared with Greek geometry and astronomy. In the Jewish tradition itself, it represents a very minor companion to the ethical creation. We shall return to this earlier Jewish contribution to astronomy in the coming sections.

*** The custom of using Jewish physicians was almost universal in the courts of European Kings, Popes and Caliphs, between the IXth and XVth Centuries.

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 Umayyads, expelled by the Abbassids in 750 AD from the East and reestablishing their rule in Spain (756-1031) decided to follow the example and have their own School of Philosophy. Al Hakam II (961 - 976) collected a remarkable library. He also boosted general learning - 27 schools in Cordoba! Unfortunately, his library was completely destroyed by his reactionary successor. Anyhow, this is how Greek science came to flourish in Spain in the Xth Century.

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 **, mostly linked with the synchronization of the lunar Jewish calendar with the solar year. R. Joshua b. Hananiah (around 100 AD) [5] perfected the calendar and may even have noticed the periodical return of Halley's comet [6,7]. Another line of work was computational in its nature: Around 150 AD, R. Nehemiah [8] had published a treatise called "The Study of Measurement", providing rules for the evaluation of areas and volumes, but with no proofs. It is very interesting to note that, with all of Greek geometry to learn from, the new start in geometry by the great Moslem algebrist (of Uzbek origin) Muhammad Ben Musa Al-Khwarizmi, a member of Al-Ma'mun's House of Wisdom, was entirely based on R. Nehemiah's treatise. Even the motivation and general approach also follow Nehemiah, being entirely computational [9]. ***

It was also in the Xth Century in Babylon, under the Abbassids, that R. Sa'adiah Gaon (882-942)[10], 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.

------------------
* It is probable that the initial move was already initiated by Harun al-Rashid himself and formalized by his successor.

** Since the Babylonian exile, the (lunar) months of the Jewish calendar carry Babylonian names, instead of the Hebrew names used in the Bible or those appearing in the Gezzer calendar, dating from 1,000 BC (discovered in an archeological dig in central Israel, now at the Istanbul museum).

*** Euclid's "Elements" had already been translated into Arabic by al-Hajjaj ibn Yusuf ibn Matar under Harun al-Rashid; an improved version was issued by the same scholar under Al-Ma'mun; and yet Khwarizmi would have nothing to do with Greek sources and used only R. Nehemiah [9].

3. The Jewish astronomers in Spain and Provence

Abraham bar Hiyya of Barcelona (d. 1136) [11] 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 [12], 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 [13]. 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. * Whereas everybody else put the stars on a rotating sphere just beyond the Moon, Gersonides estimated the distance to the stars to be ten billion times greater, of the order of 100 light-years (in modern units). Note that the great Tycho Brahe, in his dismissal of the Copernican model, argued that it would require the universe to be much too large. Gersonides did not believe in using Ptolemy's or Hipparchus' tables. He personally remeasured everything, basing his models on his own observations only. In that, he is rather unique for that period. Levi writes [7] "no argument can nullify the reality that is perceived by the senses, for true opinion must follow reality, but reality need not conform to opinion" - certainly not the usual position in the Middle Ages.

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 **, Levi realized that it could be checked, by measuring the changes in the apparent brightnesses of Mars and looking for cyclical changes along the conjectured epicycles. These thus ceased being dogma, they were a theory that had to be experimentally verified, "a la Popper". R. Levi developed tools for these measurements, essentially pinholes and the camera obscura. The results of his observations did not fit Ptolemy's model at all. Gersonides concluded that the model was no good. He tried (unsuccessfully) to improve on it. That challenge was finally answered, of course, by Copernicus three centuries later, but Gersonides was the first and only one to falsify the Alexandrian dogma - the first known instance of modern falsification philosophy. Levi also showed that Ptolemy's model for the Lunar orbit, though reproducing correctly the evolution of the Moon's position, fails completely in predicting the apparent sizes of the Moon in its motion. Unfortunately, there is no evidence that the findings had an impact on later generations of astronomers, even though Gersonides' writings were translated and available. ***

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) [18]... 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" [19] 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 [20]. 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 ****. Comparing with the case of Gersonides, it is ironic that the Popperian experimental refutation of Ptolemy's model had no impact, whereas Crescas' philosophical criticism did catch. Crescas lost a son in the anti-Jewish riots of 1391.

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 [21]. 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.

---------------
* I have conjectured that Gersonides might have derived lower bounds for stellar distances by using the figures for the distances to the Moon and planets to evaluate an "average" magnitude for stellar proper motions. Juxtaposing this datum with the fact that the shape of the constellations had not changed since the times of the Greeks (i.e. in more than a thousand years) he would get 10-100 light years as the minimal distance to the Dipper, for instance. It is clear, in addition, that Gersonides tried to evaluate these distances through brightness estimates in addition (he gives the size of a star as roughly what we estimate the size of a Red Giant to be)

** Levi also critisized and falsified the models suggested by the Moslem astronomer al-Bitrudji ("Alpetragius", XII Century, Spain) who rejected epicycles (like Maimonides) for Aristotelian reasons.

*** The failure of Ptolemy's Lunar model was also noticed independently (apparently) by Ibn al-Shatir [14] in the next Century.

**** It is interesting that Ibn Rushd's writings in the original Arabic have been lost; we do have a Hebrew translation (anonymous), reviewed by Moshe b. Yehoshua of Narbonne (d.1362) and a Latin one by Michael Scotus (d. ~ 1232).


4. Conclusion

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 [2]). 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.

5. References

[1]

O. Neugebauer (1957): The Exact Sciences in Antiquity, Providence (R.I.).

[2]

Y. Ne'eman: "An Evolutionary View of Jewish Humanism", address at the 1975 Jewish Educational Convention, Johannesburgh.

[3]

See for example Samuel I, 10, 10.

[4]

Y. Ne'eman (1976): In Harmony Among the Sciences, ICP pub., Washington, p. 851.

[5]

J. Podro (1958): The Last Pharisee, foreword by Robert Graves, Vallentine, Mitchell and Co., London.

[6]

Babylonian Talmud, Horayot, 10a.

[7]

P. Veron and J.C. Ribes (1979): Les Cométes, Hachette, Paris, p. 87.

[8]

S. Gandz (1970): Studies in Hebrew Astronomy and Mathematics, Ktav Pub. Hse., NY, p. 295.

[9]

B.L. van der Waerden (1980): A. History of Algebra, Springer-Verlag, Berlin, etc., pp. 1-14.

[10]

J.L. Fishman (ed.) (1924): Ray Sa'adyah Gaon - Kovetz Torani Madda'i (*: Saadiah Gaon).

[11]

J.M. Mill'as Vallicrosa (1965): La obra Forma de la Tierre, de R. Abraham bar Hiyya ha-Bargeloni, Consejo Super.de Invest. Cient'ificas, Instituto Arias Montano, Madrid-Barcelona (*: Abraham bar Hiyya).

[12]

N. Ben Menahem: Sinai, 10 (1942), 276-287; 11 (1942), 370; 24 (1949), 68-71, 230-235; 29 (1951), 271-317 (*: Ibn Ezra, Abraham).

[13]

B.R. Goldstein (1985): The Astronomy of Levi Ben Gerson (1288-1344), Springer-Verlag, NY-Berlin, etc. (*: Levi Ben Gerson).

[14]

B.R. Goldstein (1969): Preliminary Remarks on Levi Ben Gerson's Contributions to Astronomy, Proc. Israel Acad. Sci. and Hum., III, 9, Jerusalem.

[15]

S. Günther (1890): Bibliotheca Mathematica, NS IV, p. 75.

[16]

E. Renan (1893): Histoire Littéraire de la France, XXXI, pp. 620, 624.

[17]

Cf. Goldstein: Op cit. (supra, n. 13), p. 14.

[18]

Cf. Goldstein: Op cit. (supra, n. 13), p. 10-11.

[19]

A. Linde (1983): Phys. Lett., 129B, 177.

[20]

H.A. Wolfson: Crescas' Critique of Aristotle (1929), incl. bibliography, and Jew Quart. Rev., 7 (1916), 1-44, 175-221 (*: Crescas, Hasdai).

[21]

J. Bensaude (1912): L'astronomie antique au Portugal á l'épogue des grandes
découvertes, pp. 6, 18-29 (*: Zacuto, Abraham ben Samuel).