A solar eclipse recorded in 709 BCE by Chinese astronomers today offers keys to better understand Earth's rotation and the Sun's activity.
Chinese archives, such as the 'Spring and Autumn Annals', have preserved an accurate record of this event. A later description, found in the 'Book of Han', mentions a particular appearance of the Sun during the eclipse, which could correspond to the solar corona. These ancient documents offer researchers a unique testimony from the past, and with details.
To fully exploit this information, scientists had to correct the exact location of Qufu, the ancient capital of the duchy of Lu. Geographical and archaeological studies revealed an error of several kilometers (a few miles) in the coordinates previously used. This precision allowed for more accurate calculations regarding the eclipse's visibility from this site, eliminating contradictions in the initial simulations.
These adjustments lead to a better estimate of Earth's rotational speed at that time. The delta T parameter, which measures rotational variations, can thus be refined for the period around 709 BCE. These data help to date other historical astronomical events more reliably and to understand the long-term evolution of our planet.
The analysis indicates that the Sun was emerging from a period of low activity, known as the Grand Neo-Assyrian Minimum, around 709 BCE. The description of the corona shows a resumption of solar activity, consistent with the regular cycles of approximately 11 years. This interpretation agrees with reconstructions based on tree rings and radiocarbon measurements, offering independent validation for studies on solar changes.
The Chinese tradition of astronomical observation allowed for the establishment of many records of eclipses and other celestial events. These documents provide contemporary researchers with an abundance of data that can help refine and strengthen current scientific topics.