People in China will see the full moon on August 16 of the lunar calendar, the day after Mid-Autumn Festival arrives, once again. 

The revolution of the moon is about 29.5 days. The lunar month starts when the moon is located between the Earth and the sun. When the moon cannot be seen all night, this is called "Shuo" (new moon). When the sun and moon are located at both ends of the earth in the middle of the month, the moon is full. This is called “Wang” (full moon). The lunar month sometimes is 29 days and sometimes 30 days. So "Wang" may appear on the lunar 15th, 16th or 17th day. The full moon appears on the 15th and 16th day frequently, but seldom on the 17th day.

When the full moon appears, it is not yet dark, but experts say that after dark the moon is still full and the naked eye cannot tell the differences. Thus it will not effect the enjoyment of watching the moon in the night. In addition, when the moon is full, the shadows of its craters, mountains, and valleys will be observed. Therefore, the Mid-Autumn Festival is not the best time for watching the moon.

In fact, the origin of the Mid-Autumn Festival derives from the Autumn Equinox. An old saying goes: "Worship the sun in spring, the moon in autumn." The ancient Chinese chose the Autumn Equinox for making sacrifices to the moon, for they believed it was the beginning of autumn. At this point, hot and wet weather disappears, the sky is bright and clean, stars and the moon are bright: it is the best time to enjoy the full moon.