[M-IS22] History X Earth and Planetary Science

[MIS22-P01] The Pioneering Age of Planetary Observations in Japan Deduced from Kitora Star Chart and Nihon Shoki

*Akinori Saito¹ (1.Department of Geophysics, Graduate School of Science, Kyoto University)

Keywords:Star chart, Kitora Tumulus Mural Paintings , Nihon Shoki, Aska period

Planetary observations in Japan in the Asuka period were deduced from the star chart of the Kitora tumulus mural painting and descriptions in Nihon shoki. The Kitora tumulus, located in Asuka village, Nara, is estimated to have been constructed between the late 7th and early 8th centuries. Excavations since 1983 have revealed that, in addition to paintings of the four divine creatures on the walls of the stone chamber, there is a star chart on the ceiling of the chamber. This star chart has more than 219 stars depicted in gold leaf and four red circles that are presumed to be internal, equatorial, external, and ecliptic. It is accurate enough to be used as a star chart that can reproduce the position of the stars at any given time on any given date at mid-latitude. This star chart has two major errors: (1) the ecliptic is drawn inverted relative to the line connecting the celestial north pole and the Hoku-rakushi-mon star (Formal Haut star in the Piscis Austrinus constellation), and (2) the positions of the two constellations Chou-syuku (the extended net mansion) and Yoku-syuku (the wings mansion) are interchanged. These errors have been considered an indication of the lack of knowledge and interest in astronomy in Japan at the time. However, by interpreting this as a deliberate change to evade the Ritsuryo-laws, which prohibited the private possession of astronomical knowledge and instruments, it can be inferred that astronomical knowledge was respected at the time. The fact that the ecliptic was inverted indicates that the ecliptic, which represents the position of the planets, was important. It is inferred that the observation of the planets was one of the main targets of astronomical observation at that time. This can be supported by the descriptions in the Nihon-shoki. In the Nihon-shoki, descriptions of Mars and Jupiter first appear in 681 and 692, respectively, which coincide with the estimated construction period of the Kitora tumulus. I will discuss the status and social role of planetary observations in the Asuka period, when the government was developing its components as a state, such as the law, capital, era, and calendar, following the Tang dynasty in China.