This is cool. I was clued in to it by my friend Matt DeHayes, who posted a link on Facebook.
Researchers in Japan have found evidence in a spike in the amount of atmospheric Carbon-14 in AD 774 or 775 reflected in tree rings. Typically, this is the result of a supernova expelling materials into the galaxy, eventually reaching earth. However, nobody knew of any supernovae the ejecta of which would have reached Earth during that time frame, either through historic reports or astronomical data consistent with supernovae.
Then, some smart-ass undergrad at UC Santa Cruz (go Slugs!) by the name of Jonathon Allen got curious, and decided to do a Google search, finding a link to on-line transcripts of the Anglo-Saxon chronicles. In it, he found reference to the appearance of a new "red cruciform" star near the horizon. The placement and color suggest both a dust cloud obscuring some of the light and radiation, and that the "new star" would have been hidden by the sun after its initial appearance, thus explaining why there is little evidence of a supernova, and why the debris hasn't been observed by modern archaeologists.
Now, as always, it should be said that the observations of an 8th century chronicler, while valuable, were never intended to be used as astronomical data. The chronicler wrote about what he saw, but it would, of course, be filtered through the political, religious, and social attitudes and requirements of the time. So, there is a danger in taken what was written at face value, much less in concluding that this was definitely any one particular astronomical event.
Nonetheless, if further evidence comes to light, Allen may have set us on the path to solving a real, if small, historical and chemical mystery. Stuff like this makes me happy.
Allen - you're making this archaeologist happy, and this UC Santa Cruz alumni proud. Keep on doin' what you're doin'.