The Variable Earth’s Rotation in the 4th–7th Centuries: New ΔT Constraints from Byzantine Eclipse Records

Abstract

As one of the greatest astronomical spectacles, total solar eclipses have long been a subject of scientific interest and have been recorded by numerous civilizations over the millennia. These records are an essential reference for constraining and reconstructing Earth’s variable rotation (ΔT) prior to the 17th century. However, ΔT reconstructions for the 4th–7th centuries have significant uncertainties, mainly owing to a data scarcity. Here, we analyze Byzantine historical sources with reports of total solar eclipses along the Eastern Mediterranean coasts and add probable ΔT constraints on their basis. We examined five cases of total solar eclipses in 346, 418, 484, 601, and 693 CE, identified times and locations of the observations, and compared them with the existing ΔT spline curve to derive new ΔT constraints. Our results probably tighten ΔT variability in 346 CE, show a larger ΔT range in 418 CE, and give smaller ΔT ranges in 484, 601, and 693 CE. Our study tightens the existing ΔT variations and occasionally support some ΔT constraints that slightly depart from the ΔT spline curve in the latest reconstructions. Our results are consistent with contemporary ΔT constraints from other studies and offer an improved understanding of Earth’s variable rotation.