Ho Ping-Yü

Ancient and mediaeval observations of comets and novae in Chinese sources

Abstract The existing catalogues on ancient and mediaeval Chinese comets and novae known to western astronomers are neither complete nor accurate mainly because they do not generally come from the best sources available to us. In the Introduction the errors in these catalogues are discussed and the most important sources extant and the astronomical terms employed by the observers described. Comparative sources and parallel Korean and Japanese records are then given, whenever possible, together with the Chinese observations.

An 8th-century meridian line: I-Hsing's chain of gnomons and the pre-history of the metric system

A study is here made of one of the most remarkable pieces of organized field research in the early middle ages — the meridian survey directed by a Buddhist monk I-Hsing and an official astronomer Nankung Yueh in +725. At a central chain of four stations in Eastern China, at measured distances apart, covering some 200 km., observations were systematically made. It is believed that these consisted of the measurement of solstitial and equinoctial Sun shadows and of polar altitudes. The observations were also carried out at a chain of five further stations, about 2500 km in length in all, from Indo-China to the southern border of Mongolia. A single northernmost station in the vicinity of Lake Baikal had also been the scene of similar observations, thus making it possible to consider an arc of no less than 3800 km. length. The ratio of terrestrial distance units (li) to the degree, which it was one of the objects of the survey to ascertain, fixed a civil unit in a manner prefiguring the metric system of a thousand years later. The fact that I-Hsing, Nankung Yueh and their colleagues accepted this ratio as a constant may imply that some of them envisaged the Earths sphericity—a view in harmony with some of the ancient schools of Chinese cosmology, but not generally accepted by scholars in their time. The li which these astronomers desired to express in terms of the degree appears to have been one of the two usual distance units of the period, namely the “normal short Thang li”. A surprising result is that I-Hsing appears to have had remarkably accurate trigonometric tables at his disposal. The paper concludes with a study of the astronomical standardization of the li by Antoine Thomas S.J. in 1702 at the request of the Khang-Hsi emperor, nearly a century before the similar standardization of the metre in Europe.