; Korean: Ch'usǒk or Chuseok ??/秋夕; also known as the Moon
Festival, Mooncake Festival, or the August Moon Festival) is a
popular Chinese celebration of abundance and togetherness, dating
back over 3,000 years to China's Zhou Dynasty.

The Festival falls on the 15th day of the 8th lunar month of the
Chinese calendar (usually around mid- or late-September in the
Gregorian Calendar), a date that parallels the Autumn Equinox of
the solar calendar. (The name August Moon, commonly used for the
mid-autumn festival, comes from the fact that it occurs in the 8th
month of the lunar calendar—the festival does not occur during the
month of August on the Gregorian Calendar). At this time, the moon
is at its fullest and brightest, marking an ideal time to celebrate
the abundance of the summer's harvest, and reminding many of the
lore of Chang E (Chinese: 嫦娥; pinyin: Cháng'é), the mythical Moon
Goddess of Immortality. The traditional food of this festival is
the moon cake, of which there are many different varieties.
The Mid-Autumn Festival is one of the two most important holidays
in the Chinese calendar (the other being the Chinese Lunar New
Year), and is a legal holiday in several countries. Farmers
celebrate the end of the summer harvesting season on this date.
Traditionally, on this day, Chinese family members and friends will
gather to admire the bright mid-autumn harvest moon, and eat moon
cakes and pomeloes together. Brightly lit lanterns are often
carried around by children. Together with the celebration, there
appear some special customs in different parts of the country, such
as burning incense, planting Mid-Autumn trees, lighting lanterns on
towers, and fire dragon dances. Shops selling mooncakes, before the
festival, often display pictures of Chang Er, floating to the
moon.
Origin
The custom of worshipping the moon (called xi yue in Chinese) for
both the Han and minority nationalities, can be traced as far back
as the ancient Xia, and Shang Dynasties (2000 BCE-1066 BCE). In the
Zhou Dynasty (1066 BCE-221 BCE), the people celebrated the
Mid-Autumn Festival to wor**he moon.
The practice became very prevalent in the Tang Dynasty (618-907 CE)
that people enjoyed and worshipped the full moon. In the Southern
Song Dynasty (1127-1279), however, people started making round moon
cakes, as gifts to their relatives in expression of their best
wishes of family reunion. At night, they came out to watch the full
moon to celebrate the festival. Since the Ming (1368-1644), and
Qing Dynasties (1644-1911), the custom of Mid-Autumn Festival
celebration has become unprecedentedly popular.
Stories of the Mid-Autumn Festival
Hou Yi and Chang Er
While Westerners may talk about the 'man in the moon', the Chinese
talk about the 'woman on the moon'. The story of Chang E, and her
flight to the moon, is familiar to every Chinese, and a favourite
subject of poets. Unlike many lunar deities in other cultures who
personify the moon, Chang Er only lives on the moon. Tradition
places Hou Yi and Chang Er around 2170 BC, in the reign of the
legendary Emperor Yao, shortly after that of Huang Di.
There are so many variations of the Chang Er legend that one can
become overwhelmed and utterly confused. However, most legends
about Chang Er in Chinese mythology involve some variation of the
following elements: Hou Yi, the Archer; Chang Er, the mythical Moon
Goddess of Immortality; an emperor, either benevolent or
malevolent; an elixir of life; and the Moon:
Chang E flies to the moon, as Hou Yi looks on, from Myths and
Legends of China, 1922 by E. T. C. Werner Hou Yi, the archer
There are at least four variations to this story where Hou Yi was
an archer.
Version 1: Hou Yi was himself an immortal, while Chang Er was a
beautiful young girl, working in the Jade Emperor's (Emperor of
Heaven) Palace as the attendant to the Queen Mother of the West
(wife of the Jade Emperor), before her marriage. One day, Yi
aroused the jealousy of the other immortals, who then slandered him
before the Jade Emperor. Yi and his wife, Chang Er, were
subsequently banished from heaven, and forced to live by hunting on
earth. He became a famous archer.
Now at this time, there were 10 suns that took turns to circle the
earth — one every 10 days. One day, all 10 of the suns circled
together, causing the earth to scorch. Emperor Yao, the Emperor of
China, commanded Yi to kill all but one of the suns. Upon the
completion of his task, the Emperor rewarded Yi with a pill, the
elixir of life, and advised him: 'Make no haste to swallow this
pill, but first prepare yourself with prayer and fasting for a
year'. Yi took the pill home and hid it under a rafter, while he
began healing his spirit. In the midst of this, Yi was summoned
again by the emperor. While he was gone, Chang Er noticed a white
beam of light beckoning from the rafter and discovered the pill,
which she swallowed. Immediately, she found that she could fly.
Just at that moment, Yi returned home, and realizing what had
happened, began to reprimand her. Chang Er flew out the window into
the sky.
With bow in hand, Yi sped after her, and the pursuit continued
halfway across the heavens. Finally, Yi had to return to the earth
because of the force of the wind. Chang Er reached the moon, and
breathless, she coughed. Part of the pill fell out from her mouth.
Now, the hare was already on the moon, and Chang Er commanded the
animal to make a pill from it, so that she could return to earth to
her husband.
As of today, the hare is still pounding. As for Yi, he built
himself a palace in the sun as 'Yang' (the male principle), while
Chang Er is 'Yin' (the female principle). Once a year, on the 15th
day of the full moon, Yi visits his wife. That is why the moon is
full and beautiful on that night. [1]
This des.c.r.i.p.tion appears in written form in two Western Han
dynasty (206 BCE-24 CE) collections; Shanhaijing (Classic of the
Mountains and Seas, a book of travels and tales), and Huainanzi
(scientific, historical and philosophical articles, named for the
Prince of Huai). [2]

Version 2: Another version, very similar to the above story, had it
that the Emperor of Heaven, moved by the people’s suffering caused
by the 10 scorching suns, sent the archer, Prince Hou Yi, from
heaven to help Emperor Yao bring order. Hou Yi, with his wife,
Chang Er, descended to earth, carrying a red bow and white arrows
given him by the Emperor of Heaven.
Version 3: The earth once had ten suns circling over it, each
taking turn to illuminate the earth. One day, however, all ten suns
appeared together, scorching the earth with their heat. Hou Yi, a
strong and tyrannical archer, saved the earth by shooting down nine
of the suns. He eventually became King, but grew to become a
despot.
One day, Yi stole the elixir of life from a goddess. However, his
beautiful wife, Chang Er, drank it in order to save the people from
the her husband’s tyrannical rule. After drinking it, she found
herself floating, and flew to the moon. Yi loved his divinely
beautiful wife so much, he did not shoot down the moon.
Version 4: Another version, however, had it that Chang Er and Hou
Yi were immortals living in heaven. One day, the ten sons of the
Jade Emperor transformed into ten suns, causing the earth to
scorch. Having failed to order his sons to stop ruining the earth,
the Jade Emperor summoned Yi for help. Yi, using his legendary
archery skills, shot down nine of the sons, but spared one son to
be the sun. The Jade Emperor was obviously displeased with Yi’s
solution to save the earth. As punishment, he banished Yi and Chang
Er to live as mere mortals on earth.
Seeing that Chang Er felt extremely miserable over her loss of
immortality, Yi decided to journey on a long, perilous quest to
find the pill of immortality so that the couple could be immortals
again. At the end of his quest, he met the Queen Mother of the
West, who agreed to give him the pill, but warned him that each
person would only need half the pill to become immortal.
Yi brought the pill home and stored it in a case. He warned Chang
Er not to open the case, and then left home for a while. Like
Pandora in Greek mythology, Chang Er became curious. She opened up
the case and found the pill, just as Yi was returning home. Nervous
that Yi would catch her, discovering the contents of the case, she
accidentally swallowed the entire pill, and started to float into
the sky because of the overdose. Although Yi wanted to shoot her in
order to prevent her from floating further, he could not bear to
aim the arrow at her. Chang Er kept on floating until she landed on
the moon.
While she became lonely on the moon without her husband, she did
have company. A jade rabbit, who manufactured elixirs, also lived
on the moon.
Hou Yi, the builder
Hou Yi, a famous builder who built a beautiful jade palace for the
Goddess of the Western Heaven (also called the Royal Mother). In
appreciation, she gave Yi a special pill that contained the magic
elixir of immortality. But with it, came the condition and warning
that he may not use the pill until he had accomplished certain
self-purification.
His wife, Chang Er, was a beautiful but inquisitive woman. One day,
she discovered the pill, and without telling her husband, swallowed
it. The Goddess was very angry, and as a punishment, banished Chang
Er to the moon where, according to the legend, she can be seen at
her most beautiful, on the night of the bright harvest moon.
Hou Yi and the sorcerer-chieftain
Chang Er was a village girl who married Hou Yi. Pang Meng, the
sorcerer-chieftain, seeing his position threatened, tricked Yi into
believing that Chang Er had been unfaithful. Still deeply in love
with his wife, Yi fed her the elixir of immortality, and banishes
her to the moon. He realized his error, and died gazing at her
image in the sky. [3]
Chang Er and the cruel emperor
Many years after she was already the moon goddess, Chang Er looked
down upon Earth, and saw that a terribly cruel and tyrannical
emperor sat on the throne. To help the people, she allowed herself
to be reborn into the mortal world. The other members of her mortal
family were either killed or enslaved by the emperor, but Chang Er
managed to escape to the countryside.
Meanwhile, the emperor was aging, and obsessed with discovering the
elixir of life. He had people all over the land brought to him, and
demanded of them to find the elixir of life; nobody knew, of
course, but the emperor would not accept ignorance for an answer,
and executed all those who could not give him a satisfactory
reply.
In the countryside, Chang Er met the Goddess of Compassion, Guan
Yin, who proceeded to give Chang Er, a small elixir. Chang Er
brought the elixir to the emperor, but the suspicious emperor,
worrying that it was poison, demanded that Chang Er tasted it
first. She did, and showing no ill-effects, the emperor then took
the elixir, but promptly died. Chang Er also left the mortal world
as the effects of the elixir had only been delayed in her case.
Instead of dying, however, she ascended to the moon to retake her
place as the moon goddess.
The Hare - Jade Rabbit
According to tradition, the Jade Rabbit pounds medicine, together
with the lady, Chang Er, for the gods. Others say that the Jade
Rabbit is a shape, assumed by Chang Er herself. You may find that
the dark areas to the top of the full moon may be construed as the
figure of a rabbit. The animal's ears point to the upper right,
while at the left are two large circular areas, representing its
head and body. [4]
In this legend, three fairy sages transformed themselves into
pitiful old men, and begged for food from a fox, a monkey, and a
hare. The fox and the monkey both had food to give to the old men,
but the hare, empty-handed, jumped into a blazing fire to offer his
own fle**ead. The sages were very thankful for the meat and ate it
but the sages were so touched by the hare's sacrifice and act of
kindness that they let him live in the Moon Palace, where he became
the 'Jade Rabbit'.
A depiction of Chang Er and the Jade Rabbit
Overthrow of Mongol rule.The Mid-Autumn Festival also commemorates
an uprising in China against the Mongol rulers of the Yuan Dynasty
(1280–1368) in the early 14th century. As group gatherings were
banned, it was impossible to make plans for a rebellion. Noting
that the Mongols did not eat mooncakes, Liu Bowen (刘伯温) of Zhejiang
Province, advisor to a Chinese rebel leader Zhu Yuanzhang, came up
with the idea of timing the rebellion to coincide with the
Mid-Autumn Festival. He sought permission to distribute thousands
of moon cakes to the Chinese residents in the city to bless the
longevity of the Mongol emperor. Inside each cake, however, was
inserted a piece of paper with the message: 'Rise against the
Tartars on the 15th day of the Eighth Moon' (八月十五杀鞑子). On the night
of the Moon Festival, the rebels successfully attacked and
overthrew the government. What followed was the establishment of
the Ming dynasty (1368-1644), under the rebel leader Zhu Yuanzhang.
Henceforth, the Mid-Autumn Festival was celebrated with moon cakes
on a national level.

Vietnamese version
The Vietnamese version of this holiday is said to have originated
in the 8th century, during the reign of Emperor Minh-Hoang. Legend
had it that the Emperor took his Empress, Duong Quy Pho, to a lake
where he read a poem that he had composed to her by the light of
the moon.
A more popular version of the holiday recounts the legend of Th?ng
Cu?i, whose banyan tree uprooted and took him with it to the moon
after his wife urinated on it. Every year, on the mid-autumn
festival, children light lanterns to show Cu?i the way to get back
to Earth.
Dates
The moon festival is observed on these dates. Source is from
http://cchello1.blog.sohu.com/65088303.html