Chinese Calendar the Lunisolar Calendar — Formation, Records, Elements, Facts, and Utilizations
Today in China, people use two calendars concurrently.
One is the Gregorian Calendar, introduced in 1912 and has been used till today to better connect with the international world.
The other is the Chinese Calendar, which originated in the Xia Dynasty (2070 BC — 1600 BC), and has been revised and improved several times in history.
Chinese Calendar is also called the Agriculture Calendar or Nong Li, which notes the movement of the sun and moon, includes 12 months and 24 Solar Terms, and has been used as an accurate guide to agricultural activities.
Today, all traditional Chinese Festivals are based on the Chinese Calendar, and many people still celebrate their Nong Li birthdays.
Movement of the Moon — 12 Months in the Chinese Calendar
Movement of the Sun — 24 Solar Terms that Guide Agricultural Activities
Combination of Lunar-Solar Systems — Chinese Calendar
Record and Count System — Sexagenary Cycle

Sundial on Forbidden City, Photo from Official Site of Palace Museum.
Movement of the Moon — 12 Months
In ancient times, people found that the moon's movement was periodic, so they started to note the dates and months corresponding to the different phases, from crescent to full moon.
The moon's wax and wane period, usually 29 or 30 days long, is a month, and 12 months consist of a year.
This is named the Yin or Lunar Calendar, in which every month is represented by a kind of Lucky Flower with special cultural meanings.
However, they also realized that the movements of the moon and the sun are slightly different: 12 times of wax and wane of the moon is over 350 days, while the Revolution of Earth is around 365 days.
This disparity is a big flaw that makes the Yin or Lunar Calendar inaccurate in guiding agricultural activities.

Movement of the Sun — 24 Solar Terms
The sun is essential and influential in agricultural activities; therefore, learning about the sun's movement is very important.
Around 3000 years ago, Ji Dan, a younger brother of King Ji Fa (? — 1043 BC), found and first documented the Winter Solstice when he was trying to determine the geographical center of their kingdom by measuring the length of shadows.
After the Winter Solstice (with the longest shadow) was noted, the Summer Solstice was soon discovered.
Centuries later, the Spring and Autumn Equinoxes were recorded, when the day and night are of equal length.
The four seasonal boundaries have been documented since then.

Restored Ancient Chinese Observatory of Taosi Site of Longshan Culture (Around 2500 BC — 2000 BC) in Shanxi Province.
Until 104 BC, 24 Solar Terms had been formed and documented.
The 24 Solar Terms correspond to the sun’s positions in the ecliptic; every 15° apart along the ecliptic, there is a solar term representing the season, temperature, agricultural and natural phenomena.
It was a perfect guide for agricultural and fishery activities in The Central Plains of China, the cradle area of ancient Chinese Civilization.
Every Solar Term has an exact date, precision to second, and a poetic name.

Ancient Astronomical Observatory on Mount Song, Built by Guo Shoujing from 1276 to 1279.
Combination Of Lunar-Solar Systems — Chinese Calendar As The Lunisolar Calendar
Taking the movement of the sun and moon into consideration, there are 12 Lunar Months and 24 Solar Terms each calendar year.
Therefore, generally, there are 2 Solar Terms in every Lunar Month.
However, because of the different movement periods of the moon and the sun, sometimes there is only 1 Solar Term in a Lunar Month.
When this situation happens, a Leap Month will be added to that year.
Within this system, there are approximately 7 Leap Months every 19 years in the Traditional Chinese Calendar.
This way, the movements of the sun and the moon are all recorded and harmonized in one lunisolar calendar, the Chinese Calendar or Nong Li, which can both note dates clearly and guide agricultural activities efficiently.

Record and Count System of Chinese Calendar — Sexagenary Cycle or Ganzhi
The Sexagenary Cycle, or Heavenly Stems and Earthly Branches (Tiangan Dizhi or Ganzhi), is the system used to count and record in the traditional calendar, Astrology, medication, Fengshui, and divination.
It was formed no later than Shang Dynasty (1600 BC — 1046 BC) and had been documented in oracle inscriptions unearthed from this era.
But why 60?

Oracle Inscriptions of the Shang Dynasty that Records The Sexagenary Cycle System — National Museum of China (Photo by Qu Jiong)
Ten Heavenly Stems or Tiangan
Except for the sun and the moon, the other five bright planets have been documented as essential stars in astrology: Venus, Jupiter, Mercury, Mars, and Saturn.
These five stars move toward and away from the earth periodically, with different influences and power; the approaching earth phase is the Yang, while the apart one is the Yin.
Therefore, the Five planets, each with two phases, together, they composed the Ten Heavenly Stems:
甲(jiǎ) 乙(yǐ) 丙(bǐng) 丁(dīng) 戊(wù)
己(jǐ) 庚(gēng) 辛(xīn) 壬(rén) 癸(guǐ)

Brocade Barcer of the Han Dynasty (202 BC — 220 AD) Recorded the Five Planets — Xinjiang Museum (Photo by Dongmaiying)
Twelve Earthly Branches or Dizhi
The Ecliptic is divided into 12 sections, and there are 12 months in a year, hence the 12 Earthly Branches:
子(zǐ) 丑(chǒu) 寅(yín) 卯(mǎo) 辰(chén) 巳(sì)
午(wǔ) 未(wèi) 申(shēn) 酉(yǒu) 戌(xū) 亥(hài)
Based on the different meanings, 6 are Yin, and 6 are Yang.
Later, 12 Chinese Zodiac Signs were formed to represent the 12 Earthly Branches.

12 Zodiac Animals Carved on Copper Mirror of the Tang Dynasty (618 — 907) — Luoyang Museum
Combination of Heavenly Stems and Earthly Branches
A Heavenly Stem and an Earthly Branch (Yin and Yang) can compose a symbol that can be used to note the year, month, date, and hour.
For instance, a Yang Heavenly Stem + a Yang Earthly Branch or a Yin Heavenly Stem + a Yin Earthly Branch can form a symbol. But a Yang Heavenly Stem + a Yin Earthly Branch cannot create a symbol.
According to this system, there are 60 combinations in the Sexagenary Cycle, hence the 60-year cycle.
Utilizations of the Chinese Calendar or Nong Li
Historically, the Chinese Calendar was used to note dates and times and guide agricultural activities.
Today, many Chinese still celebrate their birthdays based on the traditional calendar.
Some people would celebrate birthdays twice a year, one in the Chinese Calendar and one in the Gregorian Calendar.
In Traditional Weddings, some people would choose their date through divination, which is also based on the Chinese Calendar.

A Calendar Page with Gregorian Calendar Date, Traditional Chinese Calendar Date, Almanac, Auspicious and Inauspicious Activities.
Meanwhile, traditional festivals are based on the Chinese Calendar as well:
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Spring Festival or Chinese New Year: 1st of January
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Lantern Festival: 15th of January
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Qingming Festival: Qingming Solar Term
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Dragon Boat Festival: 5th of May
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Qixi Festival: 7th of July
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Ghost Festival: 15th of July
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Mid-Autumn Festival: 15th of August
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Chongyang Festival: 9th of September
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Dongzhi Festival: Winter Solstice Solar Term
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Laba Festival: 8th of December
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