Study fills significant gap in Earth’s rotation history with ancient solar eclipses

Japanese researchers have identified five total solar eclipses that occurred in the Eastern Mediterranean between 346 and 693 CE. The new data, derived from Byzantine records, shed light on Earth’s historical rotation variability.

A team of Japanese researchers from the University of Tsukuba successfully identified five total solar eclipses that took place in the Eastern Mediterranean region during the 4^th to 7^th centuries CE. These findings have significant implications for our understanding of Earth’s rotational history.

This research focused on ancient records from the Byzantine Empire, a time and place where previously identified solar eclipse records are notably scarce. The identified solar eclipses occurred in the years 346, 418, 484, 601, and 693 CE.

To corroborate the eclipse occurrences, the team required confirmation of “daytime darkness to the extent that stars appeared in the sky,” stated Assistant Professor Koji Murata of the University of Tsukuba. This darkness served as an indicator of eclipse totality, a crucial factor for the study.

The new information impacts our understanding of ΔT, the variable measuring the difference between time-based on Earth’s rotation and time independent of it. This data allows researchers to gauge changes in the actual length of a day on Earth.

Taking the example of the July 19, 418 CE eclipse, a Byzantine text reported that stars appeared in the sky during daytime, observed from Constantinople. Earlier models of ΔT for that period would have situated Constantinople outside the path of the eclipse’s totality. Based on the new data, the ΔT for the 5th century CE requires an upward revision, while adjustments for the 6^th and 7^th centuries should be downward, according to Dr. Murata.

The study also adds value to the ongoing research on other global phenomena, including sea-level variations and ice-volume variability. These can now be studied with a more refined understanding of Earth’s rotational patterns on a centennial scale.

The researchers encountered numerous challenges in their quest to identify these eclipses, primarily due to the incomplete or vague nature of ancient records. Despite this, their effort fills a significant gap in our understanding of Earth’s rotational history, providing a more robust framework for future research.

References:

¹ Byzantine solar eclipse records illuminate obscure history of Earth’s rotation – University of Tsukuba – September 15, 2022

² The Variable Earth’s Rotation in the 4th–7th Centuries: New ΔT Constraints from Byzantine Eclipse Records – Hisshi Hayakawa –  Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP) – September 13, 2022 – DOI 10.1088/1538-3873/ac6b56 – OPEN ACCESS

Featured image credit: NASA/Goddard