The team found three candidate reports in tablets held by the British Museum. The tablets, all from between 679 and 655 B.C., refer to a “red glow,” a “red cloud” or “red cover[ing] the sky.” These descriptions are similar to eyewitness reports of the northern lights from more modern sources. Researchers believe they refer to one of two types of auroral behavior that create a red glow in the sky.
It’s fairly likely that Babylonian and Assyrian astrologers from that time could have seen aurorae, the researchers said. Earth’s magnetic pole, which affects where aurorae are visible, has moved in the 2,700 years since these observations. While the pole is near North America now, it would have been in Eurasia, closer to Babylon and Assyria, during the seventh century B.C. This means the observers in the region likely saw aurorae more frequently and more strongly than they can now.
The researchers compared the timing of these potential aurora records with estimations of solar activity during the time. Tree rings preserve records of their environments each year, and scientists often analyze their chemistry to estimate past solar activity. In years when the sun releases particularly large bursts of energetic particles, tree rings have high concentrations of a radioactive form of carbon called carbon-14. Tree rings from about 660 B.C. show a spike in carbon-14 compared to previous years, so the researchers believe the records they identified may have been of aurorae that came along with that spike in solar activity.
Overall, the goal of the project is to study the history of the sun’s activity over as long a period as possible. Hayakawa references a famous remark made by Isaac Newton to describe their motivations.
“Standing on the shoulders of giants as old as ~2700 years, we can see much further,” Hayakawa wrote.