没有指南针,古人怎么定方向

A Song-dynasty book, the Pingzhou ketan, records that the master of a seagoing ship watches the stars at night, the sun by day, and the compass only in overcast weather — the compass standing third. This note deals with the long stretch before the needle appeared, and with how people nevertheless fixed their directions. The core method, given in the Zhouli, "Kaogong ji", is the gnomon: level the ground, set up a pole, draw a circle, and mark on the circumference the tip of the pole's shadow at sunrise and again at sunset. The two points are left-right symmetric about the line of true north-south; joining them gives true east-west, and folding the line back to the pole gives true north-south, so that no direction need be known in advance. At night the pole star, the one place that barely moves, and the Dipper, a dial that turns, serve as rulers. The note then sets out the archaeological evidence — the Taosi observation structure in Shanxi and tomb 45 at Xishuipo in Henan — and traces the word "sinan" from a gnomon pole to a ladle-shaped object to the magnetised needle. It closes with the way orientation entered ritual and speech. The note is descriptive; it contains no predictive claims.

(This preprint has not been peer reviewed.)