UNIFIED ANALYSIS OF OBSERVATION DATES FOR ANCIENT STAR MAPS AND CATALOGUES IN ASIA

Abstract

It is an intriguing subject in the history of astronomy to determine scientifically observation dates of stars recorded in ancient star maps and catalogues of East Asia. Most of previous studies used leastsquares fitting as a function of time between observation and calculation for a group of selected stars, and they simply took the resulting mean residuals as the dating errors. In 2014, the author of this paper was given an opportunity to perform a dating analysis of a star map drawn on the ceiling of the stone room of the Kitora tumulus discovered in 1998, located at Nara in Japan. The construction time of the tumulus had been inferred by archaeologists to be around the end of the 7th century. The main difficulty in treating stellar coordinates of Chinese origin was that their longitudes had not been measured from a common cardinal point, thus preventing us from directly using the precession theory. After trial-and-error experiments, we developed a method for analyzing the observation epoch of stars exclusively using the 28-Xiu constellations based on an interval estimation in modern statistics. This method is applicable to many historical star maps and catalogues in a unified way. Furthermore, to reduce the error range of dating, the bootstrap method for small sample sizes was introduced. As a result, we obtained 81 BC ± 42 years (for a 90% confidence level) as the observation date of the Kitora star map. The same procedure was applied, with successful outcomes, to data in the Shi shi xingjing, the Almagest catalogue, the famous stone-inscribed Suzhou tianwentu, the 28-Xiu observations by Guo Shoujing, the Japanese paper star map Koshi Gesshin-zu, and Ulugh Beg' s star catalogue. Thus, it is certain that our approach can be effectively used for other old star maps and catalogues yet unexplored.