The researchers calculated how the sun would have appeared from Qufu, the ancient Chinese capital of the Lu Duchy, during the total solar eclipse. Using this information, they analyzed the ancient description of what has been considered the solar corona—the dim outer atmosphere of the sun visible to the naked eye only during total eclipses—and found that its morphology supports recent solar cycle reconstructions for the 8th century BCE.

Their findings, published in The Astrophysical Journal Letters, provide reliable new data about Earth's rotation speed during this period and suggest the sun was becoming more active after a long quiet period, independently confirming what other scientists have found using radiocarbon analysis.

Finding the true location of an ancient capital

The total solar eclipse occurred on 17 July 709 BCE and was reported from Lu Duchy Court. Its description was found in a chronicle titled the "Spring and Autumn Annals" that was compiled roughly 2–3 centuries after the eclipse. The event was recorded as "the sun was totally eclipsed."

"What makes this record special isn't just its age, but also a later addendum in the 'Hanshu' (Book of Han) based on a quote written seven centuries after the eclipse. It describes the eclipsed sun as 'completely yellow above and below.' This addendum has been traditionally associated with a record of a solar corona. If this is truly the case, it represents one of the earliest surviving written descriptions of the solar corona," lead author Hisashi Hayakawa, Assistant Professor from the Institute for Space-Earth Environmental Research and Institute for Advanced Research at Nagoya University explained.