The Mid-Autumn is a very important Chinese festival. It falls on the 15th day of the 8th lunar month，usually in September or October. 

中秋节是中国一个很重要的节日，在农历八月十五号，通常在阳历的九月或十月。

Why Mid-Autumn Festival is Celebrated and How it Started？

Mid-Autumn Festival has a history of over 3,000 years, dating back to moon worship in the Shang Dynasty (1600–1046 BC). It’s such an important festival that many poems were written about it, stories and legends about the festival are widespread, and its origins have been guessed at and explained by generations of Chinese.

中秋节有三千多年历史，可以追溯到商代时对月亮的崇拜。因为中秋节的重要地位，历代诗人都会为中秋节写诗，关于中秋节的故事、传奇在民间广为流传，中秋节的起源也被历代中国人探究。

The term 'Mid-Autumn' first appeared in the book Rites of Zhou (周礼), written in the Warring States Period (475–221 BC). But the term only related to the time and season; the festival didn't exist at that point.

“中秋”一词最早出现在战国时期《周礼》一书中，但是该词只和时间和季节有关，当时还没有中秋节。

In the Tang Dynasty (618–907 AD), it was popular to appreciate the moon. Many poets liked to create poems related to the moon when appreciating it. There is a legend that Emperor Xuanzong of the Tang Dynasty visited the Moon Palace in his dream and heard a wonderful song.

唐代时赏月风靡，诗人在赏月之时佳作连连。据传，唐玄宗曾在梦中去往月宫并听到优美的歌声。

In the Northern Song Dynasty (960–1127 AD), the 15th day of the 8th lunar month was established as the 'Mid-Autumn Festival'. From then on, sacrificing to the moon was very popular, and has become a custom ever since.

北宋时期，农历八月十五才被正式确立为中秋节，从那以后，为月亮献祭盛行，从那以后便成为风俗。