People react in a variety of ways when some piece of information, apparently reliable, contradicts a long-held belief. Changing beliefs, especially core beliefs, is rather rare, and tends to occur only after a long process of accumulation of contrary evidence until critical mass is reached.
When I was in grade school, I had an interest in astronomy and read popular books on the subject aimed at adults. I was taught that the periodicity of this celestial body was discovered by Edmund Halley, England’s Astronomer Royal, in the early 18th century, and confirmed in 1758. This story is still the dominant textbook account on sites like this one: http://www.space.com/19878-halleys-comet.html. Years later, researching something called the Astronomy wars, I learned that the actual discoverer was John Flamsteed, Astronomer Royal before Halley, whose painstaking observations on two comets visible in 1682 led to the conclusion that they were one body and allowed orbital calculations that confirmed a pattern of recurrence already long suspected. Halley used his clout with Sir Isaac Newton, president of the Royal Academy, to obtain Flamsteed’s notes and publish them under his own name. So it’s not really Halley ’s Comet after all, and the pedestal on which that icon of the enlightenment stands has a few cracks in it.
But is the discovery Flamsteed’s? Textbooks will mention a reference by Chinese astronomers in 239 BC, the notable appearance in 1066, and perhaps the visit in 1301, which was depicted by Giotto di Bandoni in a fresco of the Nativity. In a review of historical records he compiled for writing a novel about Dante (who also witnessed and recorded the 1301 appearance) the novelist Christopher Cervasco noted that Eilmer of Malmesbury, writing in 1066, assumed that the comets of 1066 and 989 were the same comet. The scribe Eadwine, commenting on the appearance in 1145, also mentioned it as a recurring phenomenon. (http://christophermcevasco.com/2011/07/22/halleys-comet-part-3-12th-15th-centuries/) According to Cervasco, the earliest possible mention of periodicity is from the Talmud, of a star that appeared in 66AD and appears every seventy years. The recurring nature, then, was common knowledge in the Middle Ages.
What follows now is speculative in the extreme, but is based on Dante’s explicit mention in Paradiso of the Catholic Church’s reaction to Mesopotamian charts of solar eclipses, produced in the 13th century and vindicated by a total eclipse of the sun crossing Spain and Italy in 1297. At the time, the church taught that the darkness that occurred during Christ’s crucifixion in 33 AD was a solar eclipse; the Arab charts showed no eclipse in Palestine near that date. The discrepancy caused great consternation because people placed great stock both in the accuracy of the Bible and in the reliability of the heavens. Some church apologists claimed the passion was so momentous an event that it affected the movements of the sun and the moon; Dante concluded that the darkness was not an eclipse, and suggested what we now know as volcanic veiling as an alternative.
The astronomers who produced the eclipse tables had the capacity to use observations from the 989, 1066 and 1145 appearances of a comet to model its movement in the heavens and accurately pinpoint its return in 1301. However, to produce anything like a tidy model of a body with the observed characteristics is impossible in the Ptolemaic earth-centered cosmos. That model already required a great deal of fudging, but Halley’s comet clinched it. The earth revolved around the sun, not the other way around. This was a much more serious discrepancy than the lack of coincidence between celestial phenomena and specific biblical events, for it required rethinking an entire world view. The world in 1301 simply wasn’t ready for that, either in Europe or in Mesopotamia, where the most radical astronomy was also labelled as heretical. It would take another 150 years before Copernicus found currency for his heliocentric theory, which did not find immediate acceptance and was indeed still the subject of learned debate when Flamsteed began his researches in the 17th century.
Have we made significant progress in dealing with cognitive dissonance in scientific thought since the beginning of the fourteenth century? I wonder. Models of the primordial earth have been rewritten at least three times in my adult life to preserve the organic soup theory of the origins of life in the light of the discovery of increasingly ancient fossils. Philosophically, at least, our models of the cosmos still reflect a geocentric perspective.
Giotto, Adoration of the Magi, ca. 1305. Lucas. Creative Commons Flickr. Some rights reserved