Scientists say that a red aurora observed in Kyoto, Japan, 250 years ago may have been the largest geomagnetic storm in recorded history, eclipsing one in 1859 that previously held the record.

Researchers from Tokyo's National Institute of Japanese Literature (NIJL) and National Institute for Polar Research (NIPR) looked at a painting from a Japanese manuscript called Seikai (“understanding comets"), which also included commentary on a red aurora above Kyoto on September 17, 1770.

Using astrometric calculations of the night sky as it would have appeared back then, they were able to check the geometry of the aurora compared to the painting and the written account.

They found that the storm that caused it was likely to be comparable to, or even slightly larger than, the Carrington event in 1859, which remains the largest geomagnetic storm on record. They estimate the 1770 storm was 3 to 10 percent larger. Their results are published in the journal Space Weather.

"The enthusiasm and dedication of amateur astronomers in the past provides us an exciting opportunity," Kiyomi Iwahashi of NIJL said in a statement. "The diary was written by a kokugakusha [scholar of ancient Japanese culture], and provides a sophisticated description of the red aurora, including a description of the position of the aurora relative to the Milky Way."

According to Wired, they were also able to get a better constraint on how long this 1770 storm lasted, suggesting it was as long as nine days. Sunspot drawings from the time show that the area covered by the Sun by sunspots was twice as large as normal.

Geomagnetic storms are caused when solar eruptions send particles our way, and they interact with our atmosphere. They can cause a temporary disturbance of our magnetosphere, which in the modern day can affect satellites and also produce powerful aurorae.

“It was lucky for us that the 1770 storm predated our reliance on electricity," Ryuho Kataoka from NIPR said in the statement.

In their paper, the researchers note that the September 1770 event and the September 1859 event occurred 100 years apart, but it has now been 150 years since the latter event. By some accounts, this means we are probably overdue for a powerful storm.

“This is a matter of a high-risk and low-probability natural hazard in the space age,” they write.

We’re not completely unprepared of course; the Space Weather Prediction Center (SWPC) in the US tells people when to watch out for powerful storms and shut satellites or power stations off appropriately. There’s even been a proposal to launch a huge magnetic shield into space to deflect incoming solar particles.

But, you know, we might want to start brushing up on our knowledge of geomagnetic storms in the mean time. Just in case.

(H/T: Wired)