How Jewish astrologers used astrolabes to predict the future
A 14th century astrolabe from Spain
If you are reading this over Shabbat, then it is safe to assume that the world did not come to an end on December 21, despite the predictions of the Mayan calendar.
But the Mayans were not the only people to look to the universe in order to predict the future. In the medieval era, scientists from various cultures used devices called astrolabes to study the cosmos and use what they saw to draw up charts or horoscopes from which they could make predictions.
At the height of their use, between the 12th and 14th centuries, astrolabes were popular in the Arab and Christian worlds. They were viewed as valuable objects, often found in royal courts and frequently decorated with precious gems.
The instruments, the majority of which were about the size of a small plate, were also used by Jewish astrologers, both for their own interest and also to offer Christian or Muslim patrons predictions about the power of their leaders and what to expect from the future.
Although some Jewish scholars, including Maimonides, were sceptical about and even critical of astrology, astrolabes were not in themselves considered magical objects.
“Astrologers used them for teaching their students how the cosmos operated,” said Professor Charles Burnett, who is leading a study into the use of astrolabes in medieval Jewish society.
“They gave a very good image of how the stars traversed the heavens.”
This meant they could be used to tell the time and check longitude or the heights of the sun and the moon. Jewish scholars would often use them to calculate the times of Shabbat or the dates for the new moon.
But, according to Prof Burnett, others used them in a more superstitious manner, to “calculate” auspicious dates for a marriage or to see what lay ahead for a child born on a particular day.
By the end of the 14th century, the use of astrolabes declined, replaced by other astrological instruments and clocks, although they were being used as late as the early 19th century in the Ottoman Empire.
Up until now, little research has been conducted into how astrolabes were used by medieval Jews, although they are referred to by the influential Jewish scholar Abraham Ibn Ezra and an image of one appears on a 14th century manuscript of Maimonides’s Guide for the Perplexed.
Their use is now the subject of Prof Burnett’s study, which is being carried out over three years by experts at the Warburg Institute and Oxford University’s Museum of the History of Science.
The researchers have gathered a list of around 20 astrolabes with Hebrew inscriptions and 150 texts relating to how they were built or used, but are hoping to locate more that may be in private collections or have been sold at auction.
The intention is to collate images and the information in a monograph, offering historians an insight into the Jewish community and culture of the period.
“They were also used as beautiful display instruments by noblemen,” said Prof Burnett. “So some may be with people who don’t even know what they are.”