The Mid-Autumn Festival falls on different days almost every year, according to western calendar. As pretty much all Chinese holidays, it is rooted in lunar calendar.
Mid-Autumn Festival is on lunar August 15th. August is the second, as well as middle, month of autumn. The moon is always at its fullest in the middle of the lunar month.
Lunar calendar August 15th: 农历八月十五
(listen:) lunar august 15
• 农: agriculture. Pronunciation: nóng (2)
• 历: calendar. Pronunciation: lì (4)
Not surprised that agriculture is closely link to calendar – they’ve got to work it:)
• 八: eight. Pronunciation: bā (1)
• 月: month or moon. Pronunciation: yuè (4)
• 十: ten. Pronunciation: shí (2)
• 五: five. Pronunciation: wǔ (3)
• 日: day or sun. Pronunciation: rì (4)