Chaucer the astronomer

Geoffrey Chaucer left scholars an intriguing puzzle in his 14th-century "Canterbury Tales." In the "Franklin's Tale," he describes a "magical" illusion that made rocks off the Brittany coast seem to disappear. This has been considered mere poetic license, invoking magic to advance the plot. But could it actually have happened?

Astronomer Donald Olsen at Southwest Texas State University says it probably was an actual 14th-century event in which unusually high tides covered the rocks. He surmises that Chaucer knew about this phenomenon. Read in this perspective, the "Franklin's Tale" makes the magician appear to be a charlatan who pretends that his "magic" produces what actually is a predictable natural event.

In the tale, a young squire tries to seduce the wife of a noble knight. She puts him off by promising to yield to his advances if he can make jagged off-shore rocks disappear so boats can sail up to the shore. He arranges to pay the magician 1,000 to create a magical illusion of vanishing rocks. However, the latter insists that the timing must be right.

The magician then uses elaborate calculations - similar perhaps to those of Dr. Olsen - to specify the moment. Chaucer says it was in "the cold and frosty season of December." Olsen calculates that the sun and moon were in position to raise enormous tides off Brittany on Dec. 19, 1340, about the time of Chaucer's birth. They were aligned for an eclipse. Moreover, both bodies were almost as close to Earth as they ever get. This won't happen again until the year 3089.

Describing his conclusions in Sky & Telescope magazine, Olsen notes that Chaucer, who was well-versed in astronomical calculations, probably had noted this alignment in casting his own horoscope. In fact, the "Franklin's Tale" alludes to tides when the squire tries futilely to invoke the sun god and moon goddess to raise the waters. He then turns to the magician. It would seem that Chaucer gave a more sophisticated spin to the tale than scholars have imagined.

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