How Ancient Texts Can Shed Light on Auroras

Rumors of a strange and terrifying event swept Japan in early September 1859. The “sky seemed to be burning,” according to one diarist. From Aomori Prefecture on the northern edge of the country’s main island to Wakayama, more than 600 miles south, the sky glowed red. Many assumed it was the light of distant fires, but no one could decide where they burned. Had a thousand houses been destroyed in Minato? Or liquor stores at Hyogo or Nishinomiya? Residents of these places assumed there’d been fires elsewhere. Koyasan, Gojo, Hashimoto and even Russia were all suggested as places that could be burning.

The historian of Shingu, a city 80 miles south of Kyoto in Wakayama, noted that “red vapor” in the northern sky had also been seen 90 years earlier in September 1770. Reports during that event similarly hypothesized that the strange light was the result of faraway fires, though other unusual effects appeared, too. One account noted that “white stripes like rods appeared within intensive red vapor,” which covered half the sky. Some people feared the world would end. They dedicated divine dances and prayed to Buddha while the eerie lights streamed through the sky, according to another account.

Scientists now understand that these frightening displays were auroras. When seen in the northern sky, the effect is also known as the northern lights or aurora borealis. The phenomenon is the result of charged particles from the sun or other sun-like stars traveling down Earth’s magnetic field lines and interacting with gases in our atmosphere. Green and red light is given off by interaction with oxygen; blue and purple by nitrogen.

Usually these light displays are visible only at the poles, but during severe geomagnetic storms, the aurora can be seen closer to the equator. This expanded visibility is a key indicator of the intensity of solar activity. During the 1770 and 1859 events, the lights were seen around the world and at exceptionally low latitudes. Although descriptions of these events from Europe and the Americas had been studied extensively, less analysis had been conducted of similar records in East Asian archives.

Now, an interdisciplinary team of Japanese researchers has been compiling and studying these records, as well as identifying new ones, as far back as 10,000 B.C.E. Extending this history, they hope, will lead to better modeling of future solar activity. That modeling is important now, as we are approaching a period when the sun’s magnetic field will be unstable and solar storms are predicted to be more frequent and intense.

The multiday 1859 event is the most severe solar storm observed during the modern era; it damaged telegraph cables on Earth, reportedly sparking fires at telegraph offices and shocking operators. The aurora was even visible in such low-latitude places as the Bahamas and Hawaii.

The damage from a solar storm of this magnitude today would have much more disastrous results, as electronic systems have proliferated since the 19th century. Electrical storms can short-circuit the power grid, as occurred in Quebec in 1989 when millions of people were left without power in the cold of late winter. Jaymie Matthews, an emeritus astronomer at the University of British Columbia, says that satellites, communications networks and the power grid could all be destroyed by a storm on the scale of the 1859 event. “If it happened in the winter, you wouldn’t have any power at all, and it’s a long time before you get it back,” he says.

He warns of possible mass casualties due to loss of power used for heating and food refrigeration, and he says restoring the networks that provide power could take months. One agency has estimated that the cost of disruptions and repairs after such a severe storm could reach $2 trillion.

Although we now know that the world won’t end when the sky streams red or green light, we need proper preparation to protect the electronic infrastructure that has become necessary to supporting human life on Earth. Matthews and others suggest creating more robust systems that have multiple backups already in place could ensure that alternates are immediately available in the event of damage or destruction.

This most recent chapter in the historical quest to compile evidence of past auroras started in 2014 when two Japanese graduate students were chatting at a pub near Kyoto University. Harufumi Tamazawa, an astronomer, was out for drinks with Hisashi Hayakawa, a historian who had been researching medieval transportation networks in East Asia. “Every time I met someone who was interested in history or could read historical documents,” says Tamazawa, “I would ask about records of low-latitude auroras.”

Hayakawa agreed with Tamazawa that finding such records might be possible, and he was interested because the topic was close to the research he’d originally hoped to pursue during his graduate work in the humanities. He’d wanted to “study past environmental variability using historical records,” but a professor advised him against it.

The pair dug in, their research enabled by a major breakthrough by another Japanese scientist in 2012: The physicist Fusa Miyake discovered that superflares appeared to leave datable signatures in tree rings. During a space weather event, Earth is bombarded with cosmic rays, which produce radioactive isotopes including carbon-14 when they reach the planet’s atmosphere. Trees take this in as part of the photosynthesis process, embedding the radioactive material in an annual timeline. Researchers have since identified ten major carbon-14 spikes, now known as Miyake events, in tree ring chronologies.

The astronomer and the historian sought out observational evidence for one of these events in the historical record. Hayakawa turned to the Songshi, a Chinese historical chronicle of the Song dynasty that includes a section on astronomical observations made between 960 to 1279 C.E. Earlier research had connected various descriptions of “vapor,” “cloud” and “light” to the aurora. Reviewing and narrowing down these references turned up 193 possible references to the aurora in the Songshi.

In ongoing research, Hayakawa, Tamazawa and their frequent collaborator Hiroaki Isobe, a solar physicist, expanded the search. They reviewed records related to the solar storms observed in the 1770 and 1859 events described above, and they plunged even further into the past. They have since consulted ancient Babylonian astronomical reports with the help of Near Eastern scholars and uncovered possible descriptions of auroras dating back to 652 B.C.E. They have widened their research to include other descriptors, including “unusual rainbows” or “white rainbows.” Isobe explains that with the growth of literacy in Japan during the Edo period, the number of private diarists increased. However, since these observers were often unfamiliar with classical texts that had previously described the aurora, these chroniclers used a greater variety of descriptive terms to refer to the same phenomenon, which in turn provides contemporary scientists with more clues about the aurora.

Hayakawa and Tamazawa have both since completed their graduate studies, and they have continued their interdisciplinary research. Most recently, Hayakawa, working with the independent researcher Marinus Anthony van der Sluijs, has identified the earliest known candidate aurora in the Chinese Bamboo Annals, which dates to the tenth century B.C.E. and predates previously identified examples by three centuries.

The data recorded by historical observers is crucial to building a more accurate understanding of the solar cycle. Using this data to create models of future activity may aid in predictions, but as Matthews argues, we still need more robust preparations to protect our electronic infrastructure should one of these massive storms reach Earth again.

In the meantime, historical observations unearthed by researchers including Hayakawa and Tamazawa will help us understand what the sun is doing in the long term, according to Leif Svalgaard, a solar physicist at Stanford University. “As always, the past is the key to the present (and future),” he writes in an email. “We need to know if what we observe now is unusual or just the sun doing its thing.”

Kim Beil | READ MORE