Full moon is a lunar phase, in which the hemisphere of the moon facing the earth is fully illuminated by the sun and appears round. A full moon occurs when the geocentric apparent longitudes of the sun and the moon differ by 180 degrees. As the full moon corresponds to an age of about 14.8 days of the synodic month, a night with a full moon is called “Jugoya (the 15th night)” in Japanese.

The appearance of the illuminated portion of the moon as seen by an observer on the earth is called luner phases. The phases designate both the degree to which the moon is illuminated and the geometric appearance of the illuminated part. The moon appears as a new moon when the sun and the moon are on the same sides of the earth, while as a full moon when they are on the opposite side. Between the new moon and the full moon, it appears as the first quarter moon and the last quarter moon, which mean we can see half of the illuminated part. If the moon happens to align exactly with the earth and sun, then we get a lunar eclipse.

As a lunar month is about 29.531 days long, the full moon falls on around the 15th day of the lunar month in the calendars that start the month on the new moon such as Chinese Calendar. However, as there is a margin of error, a full moon does not always occur on the 15th day.

The moon on the 15th day of the 8th lunar month of the lunar calendar (usually around mid- or late-September in the Gregorian calendar), when the moon is at its fullest and brightest, is called “Chushu-no-meigetsu (the fine moon in the mid-autumn)” and people hold the Moon Festival. The full moon seems to symbolize the mysterious beauty and power of the moon.

I shall introduce an easily approachable character from nature here. Originally, 'tide' was a character combining 水 'water,' 艸 'grass' and 日 'sun' only; the 'moon' was added later. Above and below the sun are the pictograms for grass. There are also forms for this character with inverse sides. The moon was added for the first time in the Tenbun (Zhuan Wen) seal script.

In antiquity, the characters for celestial bodies such as the sun and the moon had a dot in the middle (there are exceptions), which we can see in 日 (sun, day). The dot also distinguishes ○ 'gem' (of 環) from 日, which would otherwise have been written the same. (In poetic language, the sun, moon and stars were often compared to gems. This is also the case in the Zhuang Zi).

In ancient Chinese characters (carved on tortoise plastron and oracle bones and bronze vessels), the character for 'moon' does not appear. This, of course, does not mean that people then were not interested in the moon. Probably, there was not yet an understanding of the moon's relation to the earth's gravity and tides.

The special thought and attention in Japan to the moon can be understood and is seen in Heian literature like the 'Hyakuninisshu: The Hundred Poems by One Hundred Poets.' Inclination to the moon in ancient China also is conspicuous. The character 望 engraved on bronze vessels shows that a month was divided into four weeks. Although there was no scientific discovery of gravity, this character shows not only the inclination to the moon, but also bears a relation to calm astronomical observation of the atmosphere and the clouds.

Oki Muramatsuri Furyu is held on October 19 every two years in Nakamura on Dogo, the main island of the Oki Islands in Shimane Prefecture. It is one of the three large festivals on the Oki Islands and prefecturally designated as an intangible folk cultural property.

The festival dates back to the early Kamakura period (1192-1333), when Sasaki Sadatsuna was appointed governor of Oki province. He transferred the gods of the sun and the moon from Omi province, his native country, and enshrined the god of the sun at Hachioji Shrine in Motoya and the god of the moon at Jorakuji Temple (later transferred to Ichinomori Shrine) in Nakamura. He, then, performed a festival in hope of a rich harvest by fusing the power of Yin and yang.

On the festival day, the processions carrying the gods leave the two shrines and head for the meeting place, where the ritual to unite the gods of the sun and the moon is performed. After that, various performances such as the salutation by Gyoji (sumo referee) wearing armors, Onmyo-douchi (the Yin-yang drum performance) by young men wearing makeup, Kozuma (the holy sumo tournament) by children and Urate, the sumo-dance by young men are dedicated one after another. The festival ends with the horseback archery. All are performed in accordance with ancient rituals, which make the spectators slip into delusion of seeing a history picture scroll.

Aoso Shrine in Sendai, Miyagi Prefecture, is the headquarters of Aoso shrines all over the country. It was founded in 852 by Hozumi Yasumasa, the ancestor of the current shrine priest’s family, who came to this area from Kyoto. He enshrined Amaterasu Omikami (the sun goddess), Ame no Minakanushi no Kami (the god of the universe), and Tsukuyomi no Kami (the god of the moon) in the cave where holy water sprang out; hereby the shrine is famous as the place where the sun, the stars and the moon are enshrined together.

Yasumasa taught the villagers how to grow hemp plants. It is said that the shrine name “Aoso,” which literally means Green Hemp, was derived from this episode. The shrine has been known for its divine power to cure and prevent palsy, and it is said that if you visit this shrine three times, you will never be stricken with palsy for the rest of your life.

As the Hozumi clan was involved in maritime industry, the shrine is also worshipped as the deity of navigation safety. The famous fine water “Osuzu” springs out in the precinct. A lot of visitors come to take a drink of this holy water.

Sorayoi, handed down in Chiran-cho, Minamikyushu City, Kagoshima Prefecture, is a moon festival event to appreciate the moon and the god of land for rich harvest. It is nationally designated as an Important Intangible Cultural Property.

The origin of the festival and its name is unclear. Some says the name derives from the words “Sore wa yoi,” meaning “That’s good.” Others say it is the corruption of “Sora ga yoi,” meaning “The sky looks nice.”

The festival begins when the moon rises. Two boys go into the straw house called “Warakozun,” which is placed at the center of a rice paddy and start revolving it clockwise, while other boys wearing the loincloth, straw coats and straw hats go counterclockwise, mystically dancing and singing “Sorayoi Sorayoi Sorayoiyoi.” around the Warakozun.

After the dance, the adult team vs. the children team play a tug of war three times. Then, they destroy the Warakozun and make a sumo ring out of the straw and do sumo wrestling.

Sorayoi is a mystic but enjoyable traditional event.

Hazuki is a Japanese traditional name for August on the old calendar. Hazuki (葉月) literally means “a leaf month.”

There are several theories concerning its origin. One theory states that as it falls on September to October on the Gregorian calendar, it is the month of falling leaves. Another states that it is a pun for “Inagarizuki,” which means the month when ears of rice plants swell, and still another staes that it is a pun for “Harizuki.” August on the lunar calendar is also called “Tsukimi-zuki (a moon-viewing month),” for it is the month when Chushu no meigetsu (a beautifu mid-autumn moon) can be viewed.
In the Tohoku region, a large and famous annual festivals such as Aomori Nebuta Festival (Aug. 2nd-7th), Akita Kanto Festival (Aug. 4th-8th), and Sendai Tanabata Festival are held, and people enjoy short summer

The New Moon is the lunar phase that occurs when the Moon lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth. At this time, the illuminated half of the Moon faces directly toward the Sun, and the dark portion of the Moon faces directly toward Earth, so that the Moon is invisible as seen from Earth.

A solar eclipse occurs when the ecliptic longitude of the Sun and the moon's path in celestial sphere are extremely close or overlapps, thereby the outline of the new moon can be seen as a white light ring.

The time interval between New Moons is about 29.5 days. According to Feng shui teaching, it is said that if you make two to ten wishes within eight hours right after the Moon gets into the New Moon phase, your wishes will be fulfilled.

Jugoya, or the 15th Night, refers to the 15th night of the 8th month in the lunar calendar when the moon is supposed to be especially beautiful. People enjoy looking at the moon and eating dango dumplings and taro, as well as making decorations with autumn plants such as susuki (Japanese pampas grass).

This custom comes from the mid-autumn festival in China. In Japan, in the Heian period, it became an Imperial event and was called 'Moon Feast'. Courtiers looked at the moon, wrote poems and played music.
  
Commoners called this event 'Taro Beautiful Moon' and it was a harvest thanksgiving festival, in which dumplings, taro, chestnuts and persimmons were eaten.
  
One month later, the 13th Night takes place on the 13th of the 11th month in the lunar calendar. Beans and soybeans are dedicated, and the festival was known as 'Bean Beautiful Moon'. You were supposed to enjoy the moon on both 15th and 13th Nights because if you did not, it was believed to cause bad things.
  
In some local versions of these festivals, local people are allowed to steal offerings or crops as a form of good luck, and these have formed parts of much-loved autumn or harvest festivals.