The 774 CE Event: A Radiation Spike and a Red Cross in the Sky
A sudden spike of radiation locked into tree rings in 774 CE, and an English chronicle's red cross in the sky that same year.
Tree rings worldwide show a sudden jump in carbon-14 between 774 and 775 CE, caused by a burst of cosmic radiation. Most researchers now blame an extreme solar particle storm.
In 2012 a Japanese team led by Fusa Miyake reported in Nature that cedar tree rings showed a sudden jump in carbon-14 between the growth years 774 and 775 CE. Carbon-14 is made when high-energy particles from space strike the atmosphere, and this was by far the sharpest increase ever found: about twenty times the normal year-to-year variation.
The spike soon turned up worldwide in tree rings from Germany, the United States, Russia and New Zealand, and matching increases of beryllium-10 and chlorine-36 were found in polar ice cores. The source was a burst of cosmic radiation that hit the entire Earth within a year. That pattern of evidence points to charged particles rather than light.
Early suggestions included a nearby supernova or a gamma-ray burst from colliding stars. Most researchers now attribute it to an extreme solar particle storm, many times stronger than any recorded in the space age. A smaller spike in 993 CE and older ones found since, such as around 660 BCE, show such storms recur. They are now called Miyake events.
Soon after the discovery, a student pointed out that the Anglo-Saxon Chronicle, under the year 774, reports that "a red crucifix" appeared in the heavens after sunset. Some linked it to aurora. Spikes like this have become precise time markers: in 2021 a smaller sister spike, from 993 CE, dated the Viking settlement at L'Anse aux Meadows in Newfoundland to exactly 1021 CE.
Because every tree on Earth recorded the same spike, it now works as a global timestamp, and its smaller cousin from 993 CE fixed the date of the first Europeans in the Americas to the year 1021.
The link between the chronicle's red cross and the radiation spike is suggestive but not proven; red aurora and other sky signs were commonly recorded.
