Byzantine records of solar eclipses helped to understand the history of the Earth’s rotation

09/16/2022

Japanese scientists investigated ancient texts from the 4th to the 7th centuries AD. C. to identify five total solar eclipses near the eastern Mediterranean and improve the model of Earth’s rotation over time.

The observation of total solar eclipses has been used by people for a long time and it was thanks to this that they were able to understand and later predict their occurrence. The historical records of these astronomical spectacles provide invaluable information about changes in the movement of the Earth.

In a new study published in Publications of the Pacific Astronomical SocietyJapanese experts studied records from the Byzantine Empire to identify and locate total solar eclipses observed in the eastern Mediterranean in the 4th to 7th centuries AD

These records are fundamental to understanding the variability of the Earth’s rotation throughout history. However, since the people who recorded these events in ancient times often missed key information, determining the exact time, location and duration of historical eclipses is painstaking work.

“Although the original eyewitness accounts from that period are mostly lost, the quotations, translations, etc. recorded by later generations contain valuable information,” explains co-author Associate Professor Koji Murata of the University of Tsukuba. “In addition to reliable information about position and time, we needed confirmation of a total eclipse: daytime darkness to the point where the stars appeared in the sky. We were able to determine the likely time and location of five total solar eclipses from the 4th to 7th centuries in the region of the Eastern Mediterranean in AD 346, 418, 484, 601 and 693

The key variable that sheds light on this new information is Δ T it is the difference between the time measured according to the rotation of the Earth and the time independent of the rotation of the Earth. Thus, the variations of ΔT present it is a variation of the actual length of the day on Earth.

Scientists took as an example the eclipse of July 19, 418 AD An ancient text reported a solar eclipse so complete that stars appeared in the sky, and the place of observation was determined to be Constantinople. Previous model ΔT stop this time it would place Constantinople outside the path of the total eclipse. Therefore, Δ T for the 5th century AD can be adjusted based on this new information.

“Our new ΔT data fill a significant gap and indicate that the ΔT range for the 5th century should be revised upwards and downwards for the 6th and 7th centuries,” says Dr Murata.

These new data shed light on the change in the Earth’s rotation on a centennial scale and thus contribute to improving the study of other global phenomena throughout history, such as sea level variability and ice volume.

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Image courtesy of the New York Public Library Digital Collections

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