What is the origin of the invention of the celestial disk?
The ancients believed that the dragon descended from the sky, belonging to the celestial system and being Yang. Water flows underground, which belongs to the terrane and is cloudy. Because of the displacement effect caused by the relative movement of heaven and earth, the celestial disk should move to the right, so Yang Junsong rotated it to the right by 7.5 degrees.
In the Song Dynasty, twenty-eight nights and five planets were introduced, and a human plate was added, also called "Laipan", which was specially used to eliminate sand and ward off evil spirits. The Twenty-four Mountain of Renpan rotates 7.5 degrees counterclockwise relative to the Twenty-four Mountain of Ruins.
In order to determine the direction, in addition to the compass, it is also necessary to have the cooperation of the azimuth disk. The azimuth disk is still 24 directions, but the disk has evolved from a square to a circle. In this way, the orientation can be determined only by looking at the position of the magnetic needle on the orientation board.