On the 15th day of the 8th month of the lunar calendar, the moon is at the fullest. The round shape to a Chinese means family reunion. Therefore the Mid Autumn Festival or Moon Cake Festival is a day for members of a family to get together wherever it is possible.
Mid-Autumn Festival is also known as “Harvest Festival”.
This festival signals that the year's hard work in the fields will soon come to an end, with only the harvest left to attend to. People use this opportunity to express their gratitude to heaven (represented by the moon) and earth (symbolized by the earth god) for the blessings they have enjoyed over the past year.
The round "moon cakes" eaten on this festival are symbolic of family unity & closeness and also reflects people's pursuit of a round and perfect life.
Watching the moon, while eating these cakes is a custom, which is meant to encourage people to seek the brightness of the moon in their journey through life.
“水调歌头 Shui diao ge tou” is the most popular poem about the moon and the moon festival. (now in pop music too :)
水调歌头 The Moon Festival (苏轼 Su shi)
明月几时有, 把酒问青天。
不知天上宫阙, 今夕是何年?
我欲乘风归去, 又恐琼楼玉宇,
高处不胜寒, 起舞弄清影,
何似在人间!
转朱阁,低绮户,照无眠。
不应有恨, 何事长向别时圆?
人有悲欢离合, 月有阴晴圆缺,
此事古难全。
但愿人长久,千里共婵娟。
(English Translation)