A new study of ancient Chinese astronomical records of the Zhou Dynasty has strengthened the case that a solar eclipse observed on July 17, 709 BCE, could be the earliest reliably dated total solar eclipse. 

The records, which date back more than 2,700 years, may even contain the first description of the Sun’s corona, Space reports. 

The eclipse is mentioned in the chronicle Spring and Autumn Annals, compiled a few centuries after the event in the court of the ancient Chinese State of Lu. 

A later addendum in the Book of Han describes the eclipsed Sun as “completely yellow above and below,” a phrase that astronomers believe may refer to the solar corona: the faint outer atmosphere of the Sun, usually visible only during a total eclipse. 

Previous attempts to model the eclipse had failed to place the eclipse’s path over Qufu, the ancient capital of the Lu State. However, the new research corrects a long-standing error, as it turned out that the coordinates used for Qufu were off by roughly 8 kilometres. 

That correction helped the researchers accurately estimate Earth’s rotation during the eclipse, determine the tilt of the Sun’s rotational axis, and recreate how the corona likely appeared during the event. This modelling confirmed that the total eclipse would indeed have been visible at that time. 

The refined dataset, they say, corrects long-standing inaccuracies in previous reconstructions of historical astronomical events. “This work improves the precision of dating and modelling past eclipses and Earth’s rotation,” said coauthor Mitsuru Sôma of Japan’s National Astronomical Observatory.

“By pairing their careful written records with modern simulations and historical research, we can uncover new clues about our planet and our star even from events that took place thousands of years ago,” said researcher Meng Jin of the Lockheed Martin Solar and Astrophysics Laboratory, who also coauthored the study.