A Poet's Diary. Red Vapors Over Kyoto. Buried Timber. All Evidence of a Medieval Solar Storm.

In February 1204, a Japanese poet named Fujiwara no Teika looked north from Kyoto and saw what he described as "a strange red vapor in the sky, which stretched across the heavens and remained visible for several nights." Those lights were auroras, produced by a solar storm that had struck Earth several years earlier.

The breakthrough came from researchers at the Okinawa Institute of Science and Technology, who developed a refined method for tracking traces of ancient solar proton events hidden inside preserved wood. These events occur when violent eruptions from the Sun accelerate charged particles to enormous speeds, sometimes approaching 90 percent of the speed of light. The answer was in the wood. Carbon-14 levels in buried timber from Aomori Prefecture spiked in a pattern that points directly to a sub-extreme solar proton event. Comparing tree-ring data from the region allowed the team to narrow the event's timing to between late 1200 CE and early 1201 CE.

The years around 1200 fall within what scientists call the Medieval Solar Activity Maximum, a period when the Sun appears to have been particularly energetic. The findings also suggest the Sun's activity cycle ran a few years shorter during the early 13th century than it does today. Historical documents from Japan, China, Korea, Italy, France and Germany all supported the picture of elevated solar activity from the late 12th to early 13th centuries.

The stakes are not merely historical. In 1972, a series of solar proton events occurred between the Apollo 16 and 17 missions, a reminder that the gap between "documented historical curiosity" and "serious hazard to human spaceflight" is narrower than anyone would prefer.

Teika looked up at red skies and recorded his wonder and fear in a diary called The Record of the Clear Moon. Scientists listened and followed his notes to solar storms.

Read the full story at ScienceDaily, May 14, 2026

Hot Take: The trees' carbon-14 didn't care that the other witness was a poet. The data matched anyway.