九，在《易经》中属于阳数。九月九日，二九相重，故称“重九”，即所谓“是节协阳数”。现在，我国定九月九日为老年节，这是很有深意的，实为祝愿老年人健康长寿。《黄帝内经·素问》说：“天地之至数，始于一，终于九焉。”说明它是一个最高的数。因之，古时称天有九天，地? Nine, in the “I Ching” belongs to the positive number. September 9, twenty-nine weight, so called “heavy nine”, the so-called “is the Festival Association Yang number.” Now, my country is setting September 9 as the Elderly Day. This is a profound and profound wish for the elderly to live healthily and longevity. “The Yellow Emperor Nei Jing Su asked,” said: “heaven and earth to the highest number, starting in one, and finally nine Yan.” It shows that it is the highest number. Therefore, in ancient times, there are nine days in heaven and earth?