Today Nature | News reported on an effort to find evidence in medieval chronicles of a supernova that might account for a spike in carbon-14 levels: “Ancient text gives clue to mysterious radiation spike” (unfortunately, the full article is behind a paywall: “Astronomy: Clue to an ancient cosmic-ray event?”).
After hearing about elevated levels of carbon-14 in tree rings in Japan, Jonathan Allen from UC Santa Cruz did some glancing through online transcriptions of medieval chronicles. In an eigth-century Anglo-Saxon chronicle he found a reference to a “red crucifix” that appeared in the sky after sunset (scroll down to A.D. 774). Scientists quoted in the Nature | News report differ in their attitudes toward Allen’s finding. The astronomer seemed convinced
but the physicist was more skeptical. Allen’s own attitude is difficult to judge—the first line of the article suggests that he is cautious.
Caution is probably a good position to hold. Historical chronicles often report various celestial phenomena that seem difficult to interpret. That same chronicle, for example, reports that in 734 the moon appeared as if covered in blood and then in 789: “This year Elwald, king of the Northumbrians, was slain by Siga, on the eleventh day before the calends of October; and a heavenly light was often seen on the spot where he was slain….” Such historical sources are not unproblematic records of observational data that can be mined by 21st-century sciences—we might think we can explain the blood-colored moon but how would we account for the heavenly lights where the king was slain?
We must be careful to avoid cherry-picking bits simply because they confirm our assumptions while dismissing those that contradict our understanding of how nature works.
[Reposted at PACHS.]