Mystery of the most ancient solar eclipse solved

An international team of researchers revised the earliest reliably dated record of a total solar eclipse observed in ancient China in 709 BCE. This allowed for a significantly more accurate determination of how fast the Earth rotated nearly three millennia ago. The work was published in the journal The Astrophysical Journal Letters (AJL).

Modern calculations have long yielded contradictory results: according to them, the total phase of the eclipse could not have been visible from the princely court of Lu, located in the city of Qufu. Scientists realized that the problem might not be in the mathematics, but in the geography, and turned to archaeological data. It turned out that previous studies had used incorrect coordinates for ancient Qufu, missing by about eight kilometers. After correcting the coordinates, the calculations matched the observation recorded in the chronicles.

This revision became the key to more accurately determining how the Earth rotated in the 8th century BCE. The change in coordinates allowed for a more precise value of the parameter characterizing the deviation of Earth's rotation from uniform. These data help adjust previous models and clarify the timeframes of ancient astronomical events. The Earth indeed rotated faster than today: the gradual slowdown is caused by the tidal friction of the oceans under the influence of the Moon.

The work shows the significance ancient observations can have when combined with modern calculation methods. The Chinese carefully recorded celestial phenomena, as they considered them signs for the ruler, and these records continue to bring scientific discoveries millennia later. According to the study authors, the combination of ancient chronicles, archaeological data, and modern calculations literally allows us to look into the past and reconstruct the evolution of Earth's rotation and solar activity with surprising accuracy.