The ancient Han people imagined the seven nights in the east, west, north and south as four animal images, called four elephants. In the traditional culture of China, the four elephants refer to the dragon, the white tiger, the suzaku and the Xuanwu, representing the east, west, south and north respectively, which originated from the belief in the stars in ancient China.
In "Twenty-eight Nights", four images are used to divide the stars in the sky, also known as four gods and four spirits. In the theory of astronomical yin and yang in the Spring and Autumn Period, the four images refer to the natural weather of the four seasons. The concept of "Four Elephants" was highly valued in ancient Japan and Korea, which were often called "Four Saints" and "Four Holy Beasts".
In Zhouyi, the four images refer to the sun, Shaoyin, Shaoyang and Taiyin, which come from two instruments (Yang instrument and Yin instrument). Eight diagrams (dry, right, divorced, true, smoked, watched, gen and Kun) are derived from these four images.