Ancient Greeks may have observed Halley's comet fly by the earth some 226 years before the the existence of the most famous comet of them all was first recorded by Chinese or Babylonian observers.
Writing in the Journal of Cosmology, philosopher Donald Graham and astronomer Eric Hintz of Brigham Young University, reconstruct the comet's earliest probable sighting, which they say may have occurred in 466 BC, more than a couple of centuries before Chinese astronomers recorded a sighting of the comet in 240 BC.
How do they explain the abrupt shift of the time line? For starters, chalk it up to poor record-keeping.
"Whereas Babylonian and Chinese observers kept meticulous records of daily phenomena in the heavens for centuries, the Greeks do not seem to have kept similar records," they noted. "Hence it is not surprising that the Greeks have not furnished observational records with which to check the appearances of comets and the similar phenomena. Any records found in Greek sources are likely to be accidental in the sense of not arising from systematic habits."
What got the co-authors' attention was the mention of a comet falling somewhere in the Hellespont region of northern Greece, either in 466 or 467 BC. Hintz and Graham write that records from the time describe how the meteor fell even while a continued to burn in the sky. (It subsequently became a tourist attraction for the next 500 years.) However, most of the subsequent commentary focused on the meteor, giving the appearance of the comet relatively short shrift.
Fast forward to 1705. That's when Englishman Edmond Halley correctly predicted the return of a comet seen in 1682, which returned to pass by the Earth in 1758. Since then, scientists have been able to project backwards the comet's return trips, which typically take place every 75 to 76 years.
Using computer simulations Hintz and Graham suggest that what we now call Halley's comet might have been visible for about 80 days during the summer of 466 BC.
"It's tough going back that far in time. It's not like an eclipse, which is really predictable," Hintz told BBC News. "But we feel fairly good about this. If the [sighting] in 240BC is accepted, this has a fairly solid possibility..if accepted, this would be three orbits earlier [than the Chinese sighting]."