Byzantine solar eclipse records shed light on mysterious history of Earth’s rotation

Credit: New York Public Library Digital Collections

Watching a total solar eclipse is an unforgettable and perhaps most impressive experience throughout history before we could accurately understand and predict its occurrence. But the historical records of these remarkable astronomical sightings are more than just a curiosity – they provide invaluable information about changes in Earth’s motion.

In a new study in Publications of the Astronomical Society of the PacificJapanese researchers combed records from the Byzantine Empire to locate and locate total solar eclipses observed around the eastern Mediterranean in the fourth and seventh centuries CE, a period when records of previously identified solar eclipses were particularly rare.

These records are essential to understanding the diversity of Earth’s rotation throughout history. However, because the people who recorded these events in antiquity often left out key information of interest to modern astronomers, determining the correct times, locations, and ranges of historical eclipses is hard work.

“Although the original eyewitness accounts from this period have often been lost, the quotations, translations, etc., recorded by later generations provide valuable information,” explains Associate Professor Koji Murata, Associate Professor at the University of Tsukuba. “In addition to reliable location and timing information, we needed to confirm total eclipses: daytime darkness to the point where stars appear in the sky. We were able to determine the likely times and locations of five total solar eclipses from the fourth to seventh centuries in the eastern Mediterranean region, at 346 and 418, 484, 601 and 693 AD.”

The main variable highlighted by this new information is ΔT, which is the difference between time measured according to Earth’s rotation and time independent of Earth’s rotation. Thus, the differences in ΔT represent the differences in the actual length of a day on Earth.

Taking the eclipse of July 19, 418 AD as an example, an ancient text mentioned A solar eclipse So complete that stars appeared in the sky, and the observation site was identified as Constantinople. The ΔT model prior to this time had put Constantinople out of the total path for this eclipse. Therefore, the ΔT for the 5th century AD can be modified based on this new information.

Our new data fills in a large gap and suggests that the ‘fifth margin’ century The upward trend must be reconsidered, while the sixth and seventh centuries must be revised downward,” says Dr. Morata.

This new data highlights the variability of Earth’s rotation on a centigrade time scale, and thus helps to better study other global phenomena throughout history, such as sea level and ice volume variability.

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more information:
Hisashi Hayakawa et al., The Earth’s Changing Rotation in the Fourth and Seventh Centuries: New Constraints from the Records of Byzantine Eclipse, Publications of the Astronomical Society of the Pacific (2022). DOI: 10.1088 / 1538-3873 / ac6b56

Introduction of
University of Tsukuba

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