Preliminary Study of Astronomical Navigation by Zheng He

Sheng-I Hsu；Yau-Zhih Chen

地理研究叢書 氣候與人文 歷史氣候、鄭和航海、客家文化

第46號（2016 / 03 / 01）

130 - 139

英文

In the early 15th century Zheng He and his associates sailed across to the Arabian Sea many times. Each expedition involved some two hundred large ships and a crew of over 27,000 men. This fleet visited over thirty countries. They completed the voyages by means of terrestrial and astronomical navigation. Official documents about Zheng He’s expedition are sparse and meager, every piece of these records might prove to be helpful to reveal the mystery of ancient navigation techniques. Sketches printed in Wu Bei Zhi (武备志), present two types of sea maps that were used for positioning of the vessels while at sea. The first type of maps is referred to as terrestrial navigation that includes up to 40 consecutive sketches, each map is sketched in detail with mountains, rivers, islands, buildings that provide heA.D.ing direction and depth of water along the sea route from Nanjing to Hormuz. The second type of maps is called astronomical navigation that sketches the star elevation angles as observed at Pulau We, Beruwala, Dandi Bandar, Jabal Khamis, and Hormuz. Major stars used for positioning the ships include the Polaris, Gacrux, Vega, Pollux, and Procyon. Research results are summarised as follows: (1) With 3.8° polarization of the astronomical nutation (地轴章动) in 1433 A.D., Persian navigators alreA.D.y knew the technique to position their ships by telling the star elevation angle. In principle, when both the elevation angles of Polaris and Gacrux are combined to 15.5 ＂fingers＂ and its ratio is checked to the recorded value of a given location, then the positioning is completed; (2) The Sky Level IV software is employed to trace the star diagrams as recorded at Calicut step by step and we are confident to conclude that one ＂finger＂ is estimated to be equivalent to 1.57° to the best of our knowledge; (3) When four plates of the star diagrams are examined; star observing time is tabulated for each plate, misprints and errors in the diagrams are also rectified and discussed.