1、The 9th day of the 9th lunar month is the traditional Chongyang Festival, or Double Ninth Festival.

It usually falls in October in the Gregorian calendar. In an ancient and mysterious book Yi Jing, or The Book of Changes, number 6 was thought to be of Yin character, meaning feminine or negative, while number 9 was thought to be Yang, meaning masculine or positive.

So the number nine in both month and day create the Double Ninth Festival, or Chongyang Festival. Chong in Chinese means double.

Also, as double ninth was pronounced the same as the word to signify forever, both are Jiu Jiu, the Chinese ancestors considered it an auspicious day worth celebration. Thats why ancient Chinese began to celebrate this festival long time ago.

2、农历九月九日，为传统的重阳节。因为古老的《易经》中把六定为阴数，把九定为阳数，九月九日，日月并阳，两九相重，故而叫重阳，也叫重九，古人认为是个值得庆贺的吉利日子，并且从很早就开始过此节日。在古代，民间在重阳有登高的风俗，故重阳节又叫登高节。相传此风俗始于东汉。唐代文人所写的登高诗很多，大多是写重阳节的习俗;杜甫的七律《登高》，就是写重阳登高的名篇。登高所到之处，没有划一的规定，一般是登高山、登高塔。