Variable Earth's Rotation Speed in the 14th to 16th Centuries: New {\Delta}T 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 M\'ing period have not been used for {\Delta}T 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 M\'ing Dynasty. On their basis, our study revised the {\Delta}T constraint in 1361 to -408 s =< {\Delta}T =< 601 s and set new {\Delta}T constraints of 277 s =< {\Delta}T =< 890 s in 1514, -328 s =< {\Delta}T =< 332 s in 1542, and -1762 s =< {\Delta}T =< 1091 s in 1575, respectively. We also revised most of the existing {\Delta}T constraints in the 14th to 16th centuries, using the ephemeris data of the NASA JPL DE 441. Overall, our {\Delta}T constraints generally tighten the {\Delta}T variations more than what M+21 fit for their {\Delta}T spline curve, requiring downward modification and upward modifications for the {\Delta}T reconstructions around 1361 and 1542, respectively. Our results suggest that the {\Delta}T decrease between 1514 and 1567 was slightly steeper than previously considered.