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Episode 62 - Hebrew astrolabe

Hebrew astrolabe (made fourteenth century), probably from Spain

I've got the whole world in my hands - in fact, not just the world, but the cosmos. What I'm holding is a portable model of the heavens, in the shape of an exquisite, circular brass instrument that looks a bit like a large brass pocket watch, and it's called an astrolabe. With an astrolabe in my hands, I can tell the time, do a bit of surveying, work out my position in the world by sun or stars and, if that's not enough, I can also devise my horoscope.

Although perfectly familiar to the ancient Greeks, this was an instrument that was particularly important for the Islamic world, as it allowed the faithful to find the direction of Mecca, and so it's not surprising that the oldest astrolabe to survive is an Islamic one from the tenth century. But the astrolabe I'm holding is, in fact, a Jewish one. It was made about 750 years ago, in Spain. It's inscribed in Hebrew lettering, but it contains Arabic and Spanish words, and it combines both Islamic and European decorative elements. It is not just an advanced scientific instrument, but it's also an emblem of a very particular moment in Europe's religious and political history.

"There's a Spanish word that's often used to describe the relationship between the different religions and ethnic communities, which is 'convivencia', living together." (John Elliott)

"The astrolabe is much more than just a scientific instrument, it's also a symbol of knowledge. It symbolises that one understands what's going on in the heavens - one literally holds the latest knowledge in one's hands. So it has so many functions, it really is like a medieval type of Blackberry." (Silke Ackermann)

This week's programmes are about high-status objects, from all over the world, that belonged to the leaders and thinkers of around seven hundred years ago - objects that offer profound insights into the society that made them. We don't know exactly who owned the Hebrew astrolabe in today's programme, but it tells us a great deal about how Jewish and Islamic scholars revitalised science and astronomy by developing the inheritance of classical Greece and Rome. This instrument speaks of a great intellectual synthesis, and it can also tell us about a time when the three religions Christianity, Judaism and Islam all peacefully co-existed. There was, in fact, no religious synthesis, but the three faiths lived together in fruitful tension, and the friction between them made medieval Spain the intellectual powerhouse of Europe.

An astrolabe makes accessible in compact form the sum total of medieval astronomical lore. Like the latest developments today - of phone, web and particularly sat nav - this was a must-have technology, a demonstration that you were right on the cutting edge. There's a wonderfully funny and touching letter written by Chaucer to his ten-year-old son Lewis, who is obviously like techie boys in every generation, and is clamouring to get to grips with an astrolabe. As well as writing him a letter, Chaucer also wrote him a little instruction manual, telling the boy how to use the instrument, and warning him just how difficult he was going to find it. Although I suspect that, like most children today, little Lewis quickly left his father behind:

"Little Lewis, I have perceived well thy ability to learn sciences touching numbers and proportions, and I have also considered thy earnest prayer specially to learn the treatise of the astrolabe. Here is an astrolabe of our horizon, and a little treatise to teach a certain number of conclusions appertaining to the same instrument.

"Trust well that all the conclusions that can be found, or else possibly might be found, in so noble an instrument as an astrolabe, are not perfectly understood by any mortal man in this region, and I have seen that there be some instructions that will not in all things deliver their intended results; and some of them be too hard for thy tender age of ten year to understand."

I have to say that I find it as difficult to grapple with an astrolabe as little Lewis at the age of ten. It is so fiendishly clever and complicated in its structure, and it contains so much information, that it would take me the whole of this programme to describe it fully. So what follows is very summary indeed.

At first sight this astrolabe looks like an outsized old-fashioned pocket watch with an entirely brass face. It sits easily in my hand - in fact it fills it - and it's a gleaming assemblage of interlocking brass-work, with five wafer-thin discs, one on top of another, held together by a central pin. On top of this are a number of pointers that you can line up with various symbols on the discs, and this will give you astronomical readings, or help you determine your position. An astrolabe like this one is designed for the particular latitude in which it is going to be used. The five discs here will allow you to get an accurate reading from any position between the latitudes of the Pyrenees and North Africa. In the middle of the range are the latitudes for the Spanish cities of Seville and Toledo.

And that tells me that this astrolabe was almost certainly made for somebody based in Spain, who might travel between North Africa and France. And what's written on the astrolabe tells us pretty clearly what kind of person must have been using it. It tells us that the owner is Jewish, and is learned. Silke Ackermann, the curator of scientific instruments here at the British Museum, has spent a lot of time on the astrolabe's inscriptions:

"The inscriptions are all in Hebrew, you can see the finely engraved Hebrew letters quite clearly. But what's so intriguing about the piece is that not all the words are Hebrew. Some of them have Arabic origins and some are medieval Spanish. So just to give you an example, beside a star in the constellation that we call Aquila - the eagle - we can see written in Hebrew 'nesher me'offel' - 'the flying eagle'. But other star names are given in their Arabic form. So Aldebaran in Taurus has its Arabic name, 'al-dabaran', written in Hebrew letters. And when you read out the Hebrew letters for the names of the months, they give you the medieval Spanish names, like October, November, December. So what you have here is the knowledge of the classical Greek astronomers who charted the heavens, combined with the contributions of Muslim, Jewish and Christian scholars - and all of that in the palm of your hand!"

The Spain in which this astrolabe was made was the only place in Christian-ruled Europe where there were significant populations of Muslims, and it was also home to an extensive Jewish population. From the eighth to the fifteenth centuries, the mixing in medieval Spain of the people of three religions - Judaism, Christianity and Islam - was one of Spanish society's most distinctive elements. Of course, there was no such place as Spain yet, in the fourteenth century it was still a patchwork of states. The biggest was Castile, which shared a border with the last independent Muslim state in the peninsula, the kingdom of Granada. Throughout Christian Spain there were large numbers of Jewish and Muslim people, all three groups living together but keeping their separate traditions in what might be described as an early example of multi-culturalism. This coexistence, extremely rare in European history, is often referred to by the Spanish term 'convivencia'. Here's the distinguished historian of Spain, Sir John Elliott:

"Well, as I see it, the essence of multi-culturalism is the preservation of the distinctive identity of the different religious and ethnic communities in a society. And for much of the period of Islamic rule, the policy of the rulers was to accept that diversity, even if it regarded Christians and Jews as adherents of inferior faiths. The Christian rulers when they took over did much the same, because they had no other option really, and at the same time of course, there was really no intermarriage. Intermarriage was forbidden between these communities So it is a limited multi-culturalism. And that doesn't of course prevent a great deal of mutual interaction, particularly at the cultural level. So the result is a civilisation which was vibrant and creative and original, because of this contact between the three races."

This mutual interaction had, a couple of centuries earlier, put medieval Spain at the forefront of the expansion of knowledge in Europe. Not only was there growing scientific knowledge around astronomical instruments like our astrolabe, but it was also in Spain that the works of the ancient Greek philosophers - above all Aristotle - were translated into Latin and entered the intellectual bloodstream of modern Europe. And this pioneering work depended on the constant interchange between Muslim, Jewish and Christian scholars.

By the fourteenth century, this scholarly legacy was embedded in European thought, in science and medicine as well as philosophy and theology. The astrolabe became the indispensable attribute for astronomers, astrologers, doctors, geographers, or indeed anyone with intellectual aspirations - even a ten-year-old English boy like Chaucer's son.

The shared inheritance of Islamic, Christian and Jewish thinkers, would survive for centuries. But the 'convivencia' of the three faiths did not. Although medieval Spain is today often hailed by politicians as a beacon of tolerance and the model for multi-faith co-existence, the historical truth is distinctly less comfortable. Here's Sir John Elliott again.

"As regards actual religious tolerance, it's rather less clear cut than coexistence. Christendom in general, though, was a pretty intolerant society, and very opposed to deviants of all kinds. And that intolerance was particularly directed against the Jews. For instance, England expelled its Jews in 1290, and France a decade later, and as far as Christian-Muslim relations were concerned, there was a hardening of religious attitudes, really from the twelfth century onwards. And as the Christians preached the Crusades, and the Almohads who moved into Spain from North Africa, preached the Jihad, there was an increasing aggressiveness on both sides."

Against this European background of growing anti-Semitism, Christian Spain could still seem comparatively tolerant. But, there were already signs of trouble, and the survival of Muslim Granada was a reminder of unfinished business. The intellectual alliance of Christians, Jews and Muslims would soon be swept away by a militant Spanish monarchy, intent on following the rest of Europe and asserting Christian dominance. In the years around 1500, Jews and Muslims would be persecuted and expelled from Spain. The 'convivencia' was over.

Eventually, the astrolabe, this one intricate object which could do so many things, would be displaced by a whole range of separate instruments - the globe, the printed map, the sextant, the chronometer and the compass - all of them doing a part of the job that the single astrolabe could do alone.

Tomorrow we're far south of Spain, way beyond the reach of our astrolabe, in the forest world of West Africa, and again we have a high-status object which represents a huge cultural achievement. It's a sculpture, a head of a ruler from Ife in present-day Nigeria. Like the astrolabe, it's both an object of great beauty and of high technology ... and it's one that in the twentieth century would astonish the whole of Europe.

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