Around the year 660 BC, astronomers from the Assyrian Empire saw the sky turn ominously red. They wrote their observations in cuneiform writing on clay tablets. Now Japanese astronomers have linked these ancient observations to evidence of a solar storm.

In the Assyrian Empire, which existed between 2000 BC and 609 BC in what we now call the Middle East, astronomers already made observations of the universe. Usually these astronomers were educated people who, on orders of the king, made astrological predictions based on celestial omens. They wrote their observations in cuneiform writing on clay tablets. Some of these clay tablets have been preserved.

Now, a team of Japanese astronomers led by Hisashi Hayakawa of Osaka University, made a closer study of clay tablets from the seventh century BC. Among the 389 astrological records that the researchers analyzed, there were three interesting clay tablets which they named R1, R2 and R3.

Red glow

Created between 679 and 655 BC, R1, R2, and R3 contain remarkable observations by astronomers from the Assyrian Empire. Translated from cuneiform script to contemporary language, these clay tablets contain descriptions of “red glow”, “red cloud” and “red sky”, which may indicate that the astronomers witnessed a solar storm.

By dating the radioactive decay of the carbon-14 isotope in tree rings, an earlier study had already provided evidence of a massive solar storm that occurred around 660 BC. With the newly investigated descriptions on clay tablets, the Japanese team argues that a massive solar storm did indeed take place at that time.

Also after volcanic eruptions

Professor John Steele from Brown University in Providence, USA, who specializes in Babylonian astronomy, thinks that the Japanese researchers’ conclusion is plausible. The descriptions of “red glow” in particular are compelling, he says. “This terminology is relatively common, also in later descriptions.”

Professor of astrophysics Christoph Keller from Leiden University also thinks that the descriptions are telling. All the more so because it was already clear that something important happened at the same time, as was demonstrated by the carbon-14 research. However, Keller is slightly skeptical of the descriptions being attributed to a solar storm. “After volcanic eruptions, the sky can also turn red,” he says.

Visible from the Middle East

Solar storms are explosive events on the surface of the sun, during which enormous amounts of radiation and charged particles are hurled into the universe, accompanied by solar flares and plasma clouds. Sometimes these events are so intense that they can be observed from the Earth. If the Japanese researchers are correct, that was also true for the solar storm around 660 BC, which turned the sky red.

Solar storms can only be seen from the North Pole and South Pole; a good example of this is the natural display of polar lights around the Arctic and Antarctic. But at 660 BC things were different. Around that time, present-day Middle East was closer to the northern geomagnetic pole than it is now, and thus solar storms could still have been visible from there.

Incalculable damage

As our society becomes increasingly dependent on electronics and technology, solar storms will become increasingly relevant problems. In 1859 there was a massive solar storm, called the Carrington Event, which caused major disruptions for telegraphy. Telegraphy was the primary means of sending messages over long distances.

A solar storm of the same intensity reaching Earth would cause incalculable damage to our current society, with widespread electrical outages and blackouts. By mapping solar storms that occurred in the past, we might be able to predict future solar storms and protect our vulnerable electronic equipment in time.

This is a translation of the article published here.