An international research team has deciphered one of the oldest surviving human astronomical records: a description of a total solar eclipse that occurred in 709 BC, documented by sky watchers at the court of the ancient Chinese state of Lu. The Chinese account describes the Sun as becoming "completely yellow from top to bottom" during the eclipse, which may be the earliest known description of this spectacular astronomical phenomenon, the solar corona. However, verifying this account faced a historical-geographical obstacle: previously used coordinates for the ancient capital, "Qufu," were off by about eight kilometers from its actual location, according to modern archaeological evidence. After correcting the precise geographical location, scientists were able to reconstruct the astronomical scene with stunning accuracy. Their calculations revealed that in the 8th century BC, a day was shorter by about 5.5 to 6 hours compared to today. This difference is primarily attributed to the tidal effects of the Moon, which have gradually slowed the Earth's rotation over the ages. Furthermore, the analysis of the potential solar corona's morphology, inferred from the historical description, suggests that the Sun was then in an active phase of its regular 11-year magnetic cycle. This conclusion strikingly aligns with independent data from the analysis of radioactive isotopes in ancient tree rings, which also indicates that the Sun was emerging from a prolonged century-long quiet period known in astronomical records as the "Neo-Assyrian Grand Minimum." This period coincided with the rise and flourishing of the Neo-Assyrian Empire in the Middle East. Thus, this skillful combination of modern astronomy, historical geography, and the study of ancient documents not only confirms the exceptional value of Chinese astronomical records preserved by imperial dynasties over centuries but also offers new evidence of a scientific dialogue through time, where the eyes of ancient observers meet contemporary computer simulation techniques to uncover shared secrets about our Earth and Sun.
