Niâo,' he meant the star culminating at dusk at that season, at the point of observation. And so of the other stars and seasons. A Chinese astronomer at the present day would similarly express himself.
Further, the most common, and what was the earliest division of the ecliptic in China, is that of the twenty-eight lunar mansions, forming what we may call the Chinese zodiac. These mansions are grouped together in four classes of seven each, assigned to the four quarters of the heavens. Of the celestial spaces which Yâo specified, Niâo is the general name for the seven mansions or constellations belonging to the southern quarter; Hwo is an old name of what is now called Fang, the central constellation of the eastern quarter; Hsü and Mâo are the central constellations of the northern and southern quarters respectively. What Yâo meant therefore was, that his astronomers could determine the solstices and the autumnal equinox by the culmination of the stars in the mansions which he specified for those seasons. And we may assume that he directed them, for the star of the vernal equinox, to Hsing, the central mansion in the southern space Niâo. Now, Hsing corresponds to α (Alphard) Hydræ, and small stars near it, in our stellar nomenclature; Hwo, to β, δ in Scorpio; Hsü, to β Aquarii; and Mâo, to Pleiades. When we wish to make the directions of Yâo available for the purpose of chronological enquiry, the question that arises is this:—When did the above-named stars culminate at dusk in China at the equinoctial and solstitial seasons?
Bunsen tells us that Ideler, computing the places of the constellations backwards, fixed the accession of Yâo at B.C. 2163, and that Freret was of opinion that the observations left an uncertainty of 3°, leaving a margin of 210
- In the Official Book of Kâu, a work of the twelfth century before our era, Book XXVI, par. 25, in the enumeration of the duties of the astronomer royal of that day, there is mentioned the determination of 'the places of the twenty-eight stars,' meaning 'the principal stars in the twenty-eight lunar mansions.' The names of the stars and their mansions are not mentioned; surely a sufficient indication that they were even then well known. See Biot's Etudes sur l'Astronomic Indienne, &c., pp. 112, 113.