Projection Methods in East Asian Star Maps

Abstract

The celestial map of the Chunyou(淳祐) stone inscription in Suzhou (蘇小1) and that contained in the Xin yixiang ayao (新儀象法要) , both belonging to the Song (宋) Dynasty, are among the oldest of the extant celestial maps in China. The former has a circular form, and the latter is in two forms, circular and rectangular. I have been wondering which projection methods were used in these star maps, or rather, whether they were ever drawn accurately enough for us to be able to discuss their projection methods. While the stone inscription in Suzhou remains original without any change, we are not sure to which extent the star map in the Xin yixiang fayao maintains its original form, because the text underwent frequent reimpressions.

I have chosen this title for the following reason. I had a chance of analyzing two celestial maps, one from Japan and the other from Korea. The Japanese one is a rectangular star map in the Tenmon seishō zu 天文成象図, ‘Map of the arrangement of stars and constellations’), a work of the astronomer Shibukawa Harmi (渋川舂海) and his son Hisatada (昔伊), published in 1699; that from Korea is the circular star map Ch’ōnsang yōlch’a punyajido (天象列次分野之圖, ‘Chart of the constellations and the regions they govern’), originally engraved on a stone in 1395. As a result of my analyses I found that the celestial maps in the Chinese cultural area in East Asia were based on the same projection method.