A much-told story about the beginning of the Mid autumn Festival celebration comes from Niuzhu (a place in ancient Nanjing). As early as 1,600 years ago, Nanjing which was called Jianye served as capital of the Eastern Jin Dynasty. On a Mid-autumn night when Xie Shangyue, the governor of Niuzhu, was boating on a river he met Yuan Hong, a poor, frustrated but gifted scholar who had to earn his living by renting boats. Admiring his ability, Xie made friend with him and Yuan had a rise to fame with the help of Xie. Later on, having heard of the story, many refined scholars from all over the country followed suit to boat in the river, climb up the towers, and watch the moon. Famous poets like Li Bai and Ou Yangzhan were all touched by the story, and then wrote numbers of poems about it. Because of this, the tradition of watching the moon on Mid-Autumn Festival gradually came into being.
2. Season and Climate
The Mid-Autumn day is the very moment of rice maturity. And at that day farmers will worship the local God of land, whose birthday is exactly on that day. Mid-Autumn day is possibly an old tradition of telling the coming of autumn. In terms of the seasons in a year, the Mid-Autumn day can be named as “Harvest Day”, when the crops sowed in the spring can be reaped. Since ancient times, people would drink, dance, and sing on that day, celebrating the harvest. This scene can be found in the Books of Odes (the earliest collection of poems in ancient China).
According to the previous descriptions, the ancient emperors had the tradition of worshiping the moon, yet the day was initially on the day of Autumn Equinox, and not on the Mid-Autumn day. However, the Autumn Equinox is not a fixed day and there may or may not be a full moon on that day. Therefore, the day for worshipping the moon was accepted as a convention on the Mid-Autumn day, when the moon is in its fullest.
Meanwhile, it’s proven by scientific research that the inclination of the earth and the sun will gradually increase in autumn, thus the cool air up in the sky will fade away while the northwest wind is still very weak. In this way, the moisture is removed and the air in the sky would become pure and clean. So the moon would appear to be relatively fuller and bigger. And this would be the best time to appreciate the beauty of the moon.
3. Moon Cake
The tradition of eating mooncake on this festival has a long history in China, yet there are different versions of statements about its origin.
The most common version is that during the reign of Emperor Taizong of the Tang Dynasty, Taizong ordered his ablest general Li Jing to go for a battle against the Turkic clan in north ancient China to suppress their frequent invasions. The 15th day of the 8th month was exactly the day for the general’s triumphant return. In order to celebrate his victory, fireworks were set off and music was played in and out of Chang’an City (the capital of the Tang dynasty), and citizens were happily enjoying a riotous night together with warriors. At that time, a business man, coming from the Tubo Kingdom (the ancient name for Tibet), presented Taizong with a kind of round cakes to celebrate Tang’s victory. Taizong gladly received the magnificently-decorated boxes and took the multi-colored round cakes out of the boxes and handed them out to his officials and generals. From then on, the tradition of eating round moon-cakes on the Festival moon cakes was formed.
One of the legends behind this festival tells the story of a plain girl named Wuyan, who was from Qi; an ancient nation in China. Wuyan was chosen for the Emperor’s palace because of her outstanding morality but she never attracted the attention of the Emperor due to her appearance.
However, as a youngster Wuyan had worshipped the Moon and this gave her special powers so that on the night of the 15th of August, when she met the emperor in the moonlight, he saw her as beautiful and fell in love with her immediately. Wuyan later married the Emperor and became the queen of Qi, and from this moment on the tradition of worshipping the Moon on the 15th of August began.
However, young Chinese ladies to also worship the Moon for another reason – in the hope that they can become as beautiful as Chang’e, a girl who, according to Chinese legend, lives in the moon.
Source : http://www.chinatravel.com/facts/chinese-festivals/traditional-chinese-festival/Middle-Autumn-Festival.htm#1