Navigational Compass used in Ming Dynasty image source
Before the invention of artificial satellites and development of data transformation, celestial navigation played an indispensable role in human’s exploration and discovery of newfound lands. And in this blog, I would like to introduce some celestial navigating technologies implemented in Zheng He’s treasury voyage, one of the most significant expeditionary adventures recorded in the 15th century and the navigational compass and constellation map employed during the trip once again show the importance of celestial navigating in ancient times. Firstly, as shown in the figure above, based on their knowledge of magnetic declination, Chinese mariners built their advanced 48-position compass, in which the alignment of the magnetic needle always points to the direction of destination and can be calibrated by artificial measures. During Zheng He’s trip southward to Southeast Asia , one cusp of the needle stay in the direction of North Polaris and when later he switched his destination to the Persian Gulf, the mariner adjust it to point at 22.5 degree SW. Such technology reveals its importance especially in the dates when the sky is clouded over the sea. Another element that is pivotal in the success of his adventure is the constellation map. Unlike maps drawn in previous dynasties, constellation maps employed in his exploration can be separated into seven parts with different sizes and put at arm’s length to determine certain constellation’s height over horizon. And Alpha Lyrae, Pegasi, Canopus and Cassiopeia were frequently used in identifying flotilla’s position during this great adventure.