Found this intersting article while doing some research...
https://mainichi.jp/english/articles/20170923/p2a/00m/0na/021000cThe largest known geomagnetic storm ever was found to be the cause of an enormous red aurora seen across Japan in the Edo period, a research group from the National Institute of Polar Research announced in an online publication in the academic journal Space Weather on Sept. 18.
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Auroras occur due to geomagnetic storms caused by solar flares and other extraterrestrial sources disturbing the Earth's geomagnetic field. The storm simulated by Kataoka's team is estimated to be larger than the current record-holding storm that occurred in 1859.
Props to Japan for keeping such detailed records. I love this sort of puzzle solving by matching historical information against scientific predictions. It reminds me of how the
1700 Cascadia earthquake was discovered by cross-referencing an "orphan tsunami" against ghost forests in the Pacific Northwest.