Named for Guo Shou-Jing (1231–1316), a prominent Chinese astronomer of the Yuan dynasty. Believing that observations are fundamental to calendrical work and that high-quality instruments are indispensable for making satisfactory observations, he devised and constructed numerous ingenious astronomical instruments. He also conducted an expedition to measure latitudes and derived an accurate value for the obliquity of the ecliptic. (M 4420) _ _.