It is believed that the festival originated from the custom of moon worship during the Zhou Dynasty over 3,000 years ago. The term "Mid-Autumn" first appeared in the book Rites of Zhou (《周礼》):August was the middle month of the three months of autumn, and the fifteenth day of one month is the middle day of that month. Therefore, the fifteenth day of August is called "mid-autumn", or simply "mid-August".