Ancient Assyrian astronomers somehow observed solar storms without telescopes

Scientists find that ancient Assyrian astronomers knew about solar storms long before traditional detection methods.

The ancient Assyrians are famous for their incredibly accurate astronomical observations. Even so, how could they have possibly recorded solar storms without telescopes? A new study has found that ancient Assyrian observations on clay tablets correspond with tree ring data that points to increased solar activity between 680 and 650 BCE, Newsweek reports.

The discovery could help scientists predict future solar events—including solar flares and their more powerful cousins, coronal mass ejections (CMEs). When the sun throws these temper tantrums, it blasts charged particles out into space. If these tantrums target the Earth, they cause geomagnetic storms that can interfere with satellites, power grids, and communication systems.

The Past Predicts the Future

Knowing when these storms may strike is paramount in protecting the technological systems that humanity relies so heavily upon. Astronomers first started tracking these solar events with telescopes in the early part of the seventeenth century by observing sunspots. These dark areas on the surface of the sun correspond to solar flares.

However, modern researchers needed to create a longer time frame in order to spot patterns in solar storms. Thus, they turned to radiocarbon dating of the rings within trees. Moreover, researchers have looked to ancient observations to confirm the tree ring data.

“These events occurred far before the onset of instrumental observations, well outside the more modern range of wide observational coverage,” the team, led by Osaka University’s Hisashi Hayakawa, wrote in its paper. “Therefore, in order to infer the general trend of solar activity and the occurrence of CMEs, candidate auroral records have been sought in historical documents around these events.”

Auroral Red Arcs

So, how did the Assyrians know that these solar events were taking place? Like many ancient peoples, the Assyrians were astute observers of the heavens. They believed that things taking place in the sky could influence events on Earth. In a way, they were right.

Assyrian kings, often star-gazers themselves, constantly kept their observatories busy. The royal astronomers would send the king astrology reports on cuneiform tablets. Some of these tablets describe strange red skies or a “red cloud.”

Related: Ancient tree offers clues about Earth’s magnetic field reversals

The researchers believe that the Assyrian astronomers documented a phenomenon called stable auroral red arcs. When magnetic fields interact with Earth’s atmospheric oxygen, they excite electrons and cause them to emit red light.

The auroral red arcs are related to the aurora borealis and australis, commonly known as the northern and southern lights. In the sixth century BCE, the magnetic north pole was further south. Therefore, auroral red arcs would have moved south too. Thus, they could have appeared in the Middle East.

Furthermore, the team believes that the tablets represent the oldest “datable records of candidate aurorae” indicating increased solar activity between 680 and 650 BCE. It pushes back the known history of solar storms over a century. The farther back that researchers can track solar events, the better they’ll be able to predict them in the future.