An international team led by Hisashi Hayakawa, an associate professor at Nagoya University, has re-examined the oldest documented records of a total solar eclipse and used them to refine estimates of how fast our planet was rotating in the distant past, infohub.kz reports.
The event occurred on July 17, 709 BC in the state of Lu, and its description survives in the Chunqiu annals and the Han Shu compendium. The chronicles mention a total eclipse and note a "completely yellow color above and below" — which scientists regard as one of the earliest descriptions of the solar corona.
The astronomers initially ran into a contradiction: calculated trajectories showed that the path of totality should not have passed over Qufu, the capital of the state. By comparing archaeological reports with historical geography, the authors found an eight-kilometer error in the city's previously accepted coordinates.
The correction made it possible to reconstruct the eclipse precisely and to estimate Earth's rotation, which is slowing due to lunar tidal friction. The calculation yielded a Delta T value in the range of 20,264 to 21,204 seconds.
According to co-author Mitsuru Soma of the National Astronomical Observatory of Japan, the new data removed systematic distortions and improved the accuracy of dating for other celestial phenomena of antiquity. In addition, the shape of the described corona confirmed that the Sun had returned to its usual activity after a long "Homeric minimum."