When you buy through links on our articles, Future and its syndication partners may earn a commission.A red aurora like the one seen over Japan in 1204. . | Credit: Tomohiro M. Nakayama (CC-BY-NC).The solar cycle was several years shorter and the sun was experiencing an unusually active phase at the beginning of the 13th century — at least, that’s the story told by evidence left behind in tree rings and historical records that suggest a burst of protons and enhanced coronal mass ejections battered Earth between the years 1200 and 1204 CE.More specifically, scientists led by Hiroko Miyahara of the Okinawa Institute of Science and Technology (OIST) Solar–Terrestrial Environment and Climate Unit in Japan have found remnants of a dramatic solar proton event in tree rings dating back 825 years.AdvertisementAdvertisementA solar proton event, or SPE, is a barrage of protons that are accelerated to nine-tenths the speed of light by solar flares and coronal mass ejections. SPEs can be extremely dangerous, threatening astronauts and spacecraft. While Earth’s magnetic field can keep out most of the protons, occasionally some burst through Earth’s magnetic shield and descend into the atmosphere where they collide with atmospheric gases, creating atoms of a kind of carbon (carbon-14) that drift around the planet and become incorporated into living organisms — including trees.Miyahara’s team used “Meigetsuki,” which is the diary of a Japanese courtier and poet named Fujiwara no Teika who lived between 1162 and 1241, as a starting point in their search for historic SPEs. The diary said that, in February of 1204, the poet saw “red lights in the northern sky over Kyoto.” Kyoto is located at 35 degrees north, which is a rather low latitude to be witnessing …
