Variable Earth’s Rotation Speed in the 14th to 16th Centuries: New ΔT Constraints from Chinese Eclipse Records

Abstract

Total solar eclipses are not only astronomical spectacles but also great astrophysical laboratories. Their historical records are particularly helpful for assessing the past variability of the Earth’s rotation speed. Chinese records played a key role for such analyses. However, Chinese eclipse records from the Míng period have not been used for ΔT reconstructions, partially because most of the contemporaneous eclipse reports are found not in official histories but in local treatises. This study examines eclipse records in the (quasi-)contemporaneous local treatises, concentrating on what explicitly mentioned eclipse totality on the day of a total solar eclipse and what were compiled during the Míng Dynasty. On their basis, our study revised the ΔT constraint in 1361 to − 408 s ≤ ΔT ≤ 601 s and set new ΔT constraints of 277 s ≤ ΔT ≤ 890 s in 1514, −328 s ≤ ΔT ≤ 332 s in 1542, and − 1762 s ≤ ΔT ≤ 1091 s in 1575, respectively. We also revised most of the existing ΔT constraints in the 14th to 16th centuries, using the ephemeris data of the NASA JPL DE 441. Overall, our ΔT constraints generally tighten the ΔT variations more than what M + 21 fit for their ΔT spline curve, requiring downward modification and upward modifications for the ΔT reconstructions around 1361 and 1542, respectively. Our results suggest that the ΔT decrease between 1514 and 1567 was slightly steeper than previously considered.