The twenty-second solar term marks the deepest yin and the rebirth of yang, the cosmic mirror of the summer solstice. In the I Ching, this corresponds to hexagram Fu (Return), where a single yang line appears beneath five yin lines, signaling renewal from the very bottom. Taoist alchemists consider Dongzhi the most powerful day for internal cultivation, as the body’s yang qi ignites from its lowest point in the Kidneys and begins its annual ascent through the meridian system. Tang Dynasty emperors performed heaven-worship ceremonies on this day. Eating tangyuan (glutinous rice balls) symbolizes cosmic wholeness and the return of light.