BioEd Online

Want to see the astrolabe used for astronomical calculations by Geoffrey Chaucer himself? You'll be lucky, says Catherine Eagleton, a curator at the British Museum in London.

Several astrolabes have been suggested to have once belonged to Chaucer. The claims are based on the device in question's resemblance to one described by Chaucer in his Treatise on the Astrolabe, written in the late fourteenth century. Perhaps, the claimants argue, the astrolabe they now have in their collection was Chaucer's own, and served as a model for his work.

But Eagleton argues it's the other way around. It's more likely, she says, that these instruments were made after Chaucer's death, inspired by the design given in the English scholar's treatise.

"It is extremely unlikely that any of the surviving instruments were Chaucer's own astrolabe," she concludes in a paper soon to be published in Studies in the History and Philosophy of Science¹.

An astrolabe is a pocket-watch shaped device with dials and pointers for calculating the positions of the stars and the Sun. It was used for timekeeping, determining latitude, and making astrological forecasts.

Man of many talents

Born around 1343, Chaucer is most famous for his literary work known as The Canterbury Tales. But he was a man of many interests, including the sciences of his age: the Tales demonstrate a deep knowledge of astronomy, astrology and alchemy.

He was also a courtier and possibly a spy for Richard II of England. "He was an intellectual omnivore," says Eagleton. "There's no record that he had a formal university education, but he clearly knows the texts that academics were reading."

His Treatise on the Astrolabe of 1391 instructs how to use the devices, and draws instruments with some distinctive features, such as capital letters marking the 24 hours of the day, and a symbol of a dog to represent the Dog Star.

When astrolabes are found with these features, they are often labelled Chaucerian. Sometimes this alone has been used to date the instruments to the fourteenth century. And Eagleton says that some collectors and dealers have claimed that an instrument could be the very one Chaucer held.

"There's a real tendency to link any fourteenth-century instrument to him," she says, adding that museum curators are usually more careful. The British Museum doesn't make strong claims for its own Chaucerian astrolabes, for example. At Merton College in Oxford University there is an instrument generally just called "Chaucer's astrolabe", which may give people the wrong impression, she notes.

"There are probably four or five of these around," says Eagleton. They can't all be Chaucer's, she says — "no one needs five astrolabes".

In fact, none of them can be definitively dated to the fourteenth century, Eagleton says. And all four of those she studied closely, including one at the British Museum and another Chaucerian instrument at Oxford, known as the Painswick astrolabe, have features that suggest they were made after Chaucer's treatise.

For example, the brackets holding the rings of these two astrolabes have unusual designs that could be copies of the awkward drawing of a bracket in Chaucer's text, which merges views from different angles.

Star struck

This habit of linking objects to well-known figures isn't new. Chaucer was already famous by the sixteenth century, when a slew of texts and items were attributed to him.

Clearly that continues today. "There is this weird celebrity angle, where people get a bit carried away," says Eagleton. "It is always tempting to attach an object to a famous name — it's a very human tendency, which lets us tell stories about them. But it winds me up when it's done on the basis of virtually no evidence."

Of course, whether or not an astrolabe was Chaucer's would affect its price. "This association with Chaucer probably boosts the value," says Eagleton. "I might be making myself unpopular with dealers and collectors."