The twelve Earthly Branches or Terrestrial Branches  are a Chinese ordering system used throughout East Asia in various contexts,including its ancient dating system,astrological traditions,zodiac and ordinals.
This system was built from observations of the orbit of Jupiter. Chinese astronomers divided the celestial circle into 12 sections to follow the orbit of 歲星Suìxīng (Jupiter,the Year Star). Astronomers rounded the orbit of Suixing to 12 years (from 11.86). Suixing was associated with 攝提Shètí (ηBoötis) and sometimes called Sheti.
Jonathan Smith has proposed that the first meanings of the earthly branches,predating the Shang dynasty,were phases of the moon,with the heavenly stems at that point referring to divisions of the ecliptic. After being adopted as a calendar these would have lost their clear lunar reference,permitting their repurposing for Jupiter stations. 
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In correlative thinking, the 12 years of the Jupiter cycle also identify the 12 months of the year, 12 animals (mnemonics for the system), cardinal directions, seasons, and the 12 traditional Chinese units of time in the form of two-hour periods that each day was divided into. In this case an Earthly Branch can refer to a whole two-hour period, or to the exact time at its center. For instance 午時wǔshí can mean either noon or 11 am –1 pm. (The jiéqì system provided single hours and 15-degree arcs in time and space.)
Chinese seasons are based on observations of the sun and stars. Many Chinese calendrical systems have started the new year on the second new moon after the winter solstice.
The Earthly Branches are today used with the Heavenly Stems in the current version of the "traditional Chinese calendar" and in Taoism. The Ganzhi (Stem-Branch) combination is a fairly new way to mark time; in the second millennium BC, during the Shang era, the 10 Heavenly Stems provided the names of the days of the week. The Branches are as old as the Stems (and according to recent archaeology may actually be older), but the Stems were tied to the ritual calendars of Chinese kings.
|Direction||Season||Lunar Month||Double Hour|
| on'yomi of|
| kun'yomi |
of Animal / Zodiac
| on'yomi of|
| Japanese-based kun'yomi |
of Animal / Zodiac
|native kunyomi of animal zodiac|
|1||子||ㄗˇ||zǐ||zi2||chú||tsiX||し (shi)||ね (ne)||し||にー (nii)||えんちゅ (enchu)||자 (ja)||ᠬᠤᠯᠤᠭᠠᠨᠠ||ᠰᡳᠩᡤᡝᡵᡳ||tí (SV: tử)||鼠|
|鼠||0° (north)||winter||Month 11||11pm to 1am (midnight)|
|2||丑||ㄔㄡˇ||chǒu||cau2||thiú||trhjuwX||ちゅう (chū)||うし (ushi)||ちゅー||うし (ushi)||うし (ushi)||축 (chuk)||ᠦᠬᠡᠷ||ᡳᡥᠠᠨ||sửu||牛|
|30°||Month 12||1am to 3am|
|3||寅||ㄧㄣˊ||yín||jan4||în||yin||いん (in)||とら (tora)||いん||とぅら (tura)||とぅら (tura)||인 (in)||ᠪᠠᠷᠰ||ᡨᠠᠰᡥᠠ||dần||虎|
|虎||60°||spring||Month 1||3am to 5am|
|4||卯||ㄇㄠˇ||mǎo||maau5||báu||maewX||ぼう (bō)||う (u)||ぼー||うー (uu)||うさじ (usaji)||묘 (myo)||ᠲᠠᠤᠯᠠᠢ||ᡤᡡᠯᠮᠠᡥᡡᠨ||mão (non-SV: mẹo)||兔|
|兎||90° (east)||Month 2||5am to 7am|
|5||辰||ㄔㄣˊ||chén||san4||sîn||dzyin||しん (shin)||たつ (tatsu)||しん||たち (tachi)||りゅー (ryuu)||진 (jin)||ᠯᠤᠤ||ᠮᡠᡩᡠᡵᡳ||thìn (SV: thần)||龙（龍）|
|竜 (龍)||120°||Month 3||7am to 9 am|
|6||巳||ㄙˋ||sì||zi6||sū||ziX||し (shi)||み (mi)||し||みー (mii)||はぶ (habu)||사 (sa)||ᠮᠣᠭᠠᠢ||ᠮᡝᡳᡥᡝ||tị||蛇|
|蛇||150°||summer||Month 4||9am to 11am|
|7||午||ㄨˇ||wǔ||ng5||ngó͘||nguX||ご (go)||うま (uma)||ぐ||うま (uma)||んま ('nma)||오 (o)||ᠮᠣᠷᠢ||ᠮᠣᡵᡳᠨ||ngọ||马（馬）|
|馬||180° (south)||Month 5||11am to 1pm (noon)|
|8||未||ㄨㄟˋ||wèi||mei6||bī||mjɨjH||び (bi)||ひつじ (hitsuji)||び||ふぃちじ (fichiji)||ふぃーじゃー (fiijaa)||미 (mi)||ᠬᠣᠨᠢ||ᡥᠣᠨᡳᠨ||mùi (SV: vị)||羊|
|210°||Month 6||1pm to 3pm|
|9||申||ㄕㄣ||shēn||san1||sin||syin||しん (shin)||さる (saru)||しん||さーるー (saaruu)||さーるー (saaruu)||신 (sin)||ᠪᠡᠴᠢᠨ||ᠪᠣᠨᡳᠣ||thân||猴|
|猿||240°||autumn||Month 7||3pm to 5pm|
|10||酉||ㄧㄡˇ||yǒu||jau5||iú||yuwX||ゆう (yū)||とり (tori)||ゆー||とぅい (tu'i)||とぅい (tu'i)||유 (yu)||ᠲᠠᠬᠢᠶᠠ||ᠴᠣᡴᠣ||dậu||鸡（雞）|
|鶏 (鳥) |
|270° (west)||Month 8||5pm to 7pm|
|11||戌||ㄒㄩ||xū||seot1||sut||swit||じゅつ (jutsu)||いぬ (inu)||いん ('in)||いん ('in)||술 (sul)||ᠨᠣᠬᠠᠢ||ᡳᠨᡩᠠᡥᡡᠨ||tuất||狗|
|犬||300°||Month 9||7pm to 9pm|
|12||亥||ㄏㄞˋ||hài||hoi6||hāi||hojX||がい (gai)||い (i)||げー||いー (yii)||やましし (yamashishi)||해 (hae)||ᠭᠠᠬᠠᠢ||ᡠᠯᡤᡳᠶᠠᠨ||hợi||猪（豬）|
|330°||winter||Month 10||9pm to 11pm|
Some cultures assign different animals: Vietnam replaces the Ox and Rabbit with the water buffalo and cat, respectively; Tibet replaces the Rooster with the bird. In the traditional Kazakh version of the 12 year animal cycle (Kazakh : мүшел, müşel), the Dragon is substituted by a snail (Kazakh : ұлу, ulw), and the Tiger appears as a leopard (Kazakh : барыс, barıs). 
Though Chinese has words for the four cardinal directions, Chinese mariners and astronomers/astrologers preferred using the 12 directions of the Earthly Branches, which is somewhat similar to the modern-day practice of English-speaking pilots using o'clock for directions. Since 12 points were not enough for sailing, 12 midpoints were added. Instead of combining two adjacent direction names, they assigned new names:
The 24 directions are:
|Character||Mandarin name||Cantonese name||Hokkien name||Korean name||Japanese name||Ryukyuan (Okinawan)||Vietnamese name||Direction|
|1||子||ㄗˇ zǐ||zi2||chú||자 (ja)||ね (ne)||にー (nii)||tí (SV: tử)||0° (north)|
|2||癸||ㄍㄨㄟˇ guǐ||gwai3||kúi||계 (gye) (SK: 규 (gyu))||みずのと (mizunoto)||みんぬとぅ (minnutu)||quý||15°|
|3||丑||ㄔㄡˇ chǒu||cau2||thiú||축 (chuk) (SK: 추 (chu))||うし (ushi)||うし (ushi)||sửu||30°|
|4||艮||ㄍㄣˋ gèn||gan3||kùn||간 (gan)||うしとら (ushitora)||うしとぅら (ushitura)||cấn||45° (northeast)|
|5||寅||ㄧㄣˊ yín||jan4||în||인 (in)||とら (tora)||とぅら (tura)||dần||60°|
|6||甲||ㄐㄧㄚˇ jiǎ||gaap3||kap / kah||갑 (gap)||きのえ (kinoe)||ちにー (chinii)||giáp||75°|
|7||卯||ㄇㄠˇ mǎo||maau5||báu||묘 (myo)||う (u)||う (u)||mão (non-SV: mẹo)||90° (east)|
|8||乙||ㄧˇ yǐ||jyut3||it||을 (eul)||きのと (kinoto)||ちぬとぅ(chinutu)||ất||105°|
|9||辰||ㄔㄣˊ chén||san4||sîn||진 (jin) (SK: 신 (sin))||たつ (tatsu)||たち (tachi)||thìn (SV: thần)||120°|
|10||巽||ㄒㄩㄣˋ xùn||seon3||sùn||손 (son)||たつみ (tatsumi)||たちみー (tachimii)||tốn||135° (southeast)|
|11||巳||ㄙˋ sì||zi6||sū||사 (sa)||み (mi)||みー (mii)||tị||150°|
|12||丙||ㄅㄧㄥˇ bǐng||bing2||péng||병 (byeong)||ひのえ (hinoe)||ふぃにー (finii)||bính||165°|
|13||午||ㄨˇ wǔ||ng5||ngó͘||오 (o)||うま (uma)||うま (uma)||ngọ||180° (south)|
|14||丁||ㄉㄧㄥ dīng||ding1||teng||정 (jeong)||ひのと (hinoto)||ふぃぬとぅ (finutu)||đinh||195°|
|15||未||ㄨㄟˋ wèi||mei6||bī||미 (mi)||ひつじ (hitsuji)||ふぃちじ (fichiji)||mùi (SV: vị)||210°|
|16||坤||ㄎㄨㄣ kūn||kwan1||khun||곤 (gon)||ひつじさる (hitsujisaru)||ふぃちじさーるー (fichijisaaruu)||khôn||225° (southwest)|
|17||申||ㄕㄣ shēn||san1||sin||신 (sin)||さる (saru)||さーるー (saaruu)||thân||240°|
|18||庚||ㄍㄥ gēng||gang1||keng||경 (gyeong)||かのえ (kanoe)||かにー (kanii)||canh||255°|
|19||酉||ㄧㄡˇ yǒu||yau5||iú||유 (yu)||とり (tori)||とぅい (tu'i)||dậu||270° (west)|
|20||辛||ㄒㄧㄣ xīn||san1||sin||신 (sin)||かのと (kanoto)||かぬとぅ (kanutu)||tân||285°|
|21||戌||ㄒㄩ xū||seot||sut||술 (sul)||いぬ (inu)||いん (in)||tuất||300°|
|22||乾||ㄑㄧㄢˊ qián||kin4||khiân||건 (geon)||いぬい (inui)||いんいー (in'yii)||càn (SV: kiền)||315° (northwest)|
|23||亥||ㄏㄞˋ hài||hoi6||hāi||해 (hae)||い (i)||いー (yii)||hợi||330°|
|24||壬||ㄖㄣˊ rén||jam4||jîm||임 (im)||みずのえ (mizunoe)||みんにい (minnii)||nhâm||345°|
Advanced mariners such as Zheng He used 48-point compasses. An additional midpoint was called by a combination of its two closest basic directions, such as 丙午 (bǐngwǔ) for the direction of 172.5°, the midpoint between 丙 (bǐng), 165°, and 午 (wǔ), 180°.
The terrestrial branches are still commonly used nowadays in Chinese counting systems similar to the way the alphabet is used in English. For example, names in legal documents and contracts where English speakers would use K, L, M, etc. Korea and Japan also use terrestrial branches on legal documents in this way.
Since the celestial stems and terrestrial branches combined only consist of 22 characters, the four final letters – W, X, Y, and Z – cannot be represented by any of the celestial stems and terrestrial branches, and those four letters are represented by ‘物’, ‘天’, ‘地’, and ‘人’, respectively, instead. 
In case of upper-case letters, the radical of ‘口’ (the ‘mouth’ radical) may be added to the corresponding terrestrial branch or any of ‘物’, ‘天’, ‘地’, and ‘人’ to denote an upper-case letter. 
The traditional Chinese calendar is a lunisolar calendar which identifies years, months, and days according to astronomical phenomena. In China, it is defined by the Chinese national standard GB/T 33661-2017, "Calculation and Promulgation of the Chinese Calendar", issued by the Standardization Administration of China on May 12, 2017.
The ecliptic or ecliptic plane is the orbital plane of Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars. The ecliptic is an important reference plane and is the basis of the ecliptic coordinate system.
The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south of the ecliptic, which is the apparent path of the Sun across the celestial sphere over the course of the year. The orbital paths of the Moon and major planets are within the belt of the zodiac.
In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.
Traditional Chinese astronomy has a system of dividing the celestial sphere into asterisms or constellations, known as "officials".
Chinese astrology is based on the traditional astronomy and calendars. Chinese astrology came to flourish during the Han Dynasty.
An armillary sphere is a model of objects in the sky, consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic. As such, it differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations. It was invented separately first in ancient China during the 4th century BC and ancient Greece during the 3rd century BC, with later uses in the Islamic world and Medieval Europe.
The ten Heavenly Stems or Celestial Stems are a Chinese system of ordinals that first appear during the Shang dynasty, c. 1250 BCE, as the names of the ten days of the week. They were also used in Shang-period ritual as names for dead family members, who were offered sacrifices on the corresponding day of the Shang week. The Heavenly Stems were used in combination with the Earthly Branches, a similar cycle of twelve days, to produce a compound cycle of sixty days. Subsequently, the Heavenly Stems lost their original function as names for days of the week and dead kin, and acquired many other uses, the most prominent and long lasting of which was their use together with the Earthly Branches as a 60-year calendrical cycle. The system is used throughout East Asia.
In astronomy, an epoch or reference epoch is a moment in time used as a reference point for some time-varying astronomical quantity. It is useful for the celestial coordinates or orbital elements of a celestial body, as they are subject to perturbations and vary with time. These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit.
The Pig or sometimes translated as the Boar is the twelfth of the 12-year cycle of animals which appear in Chinese zodiac, in relation to the Chinese calendar and system of horology, and paralleling the system of ten Heavenly Stems and twelve Earthly Branches. Although the term "zodiac" is used in the phrase "Chinese zodiac", there is a major difference between the Chinese usage and Western astrology: the zodiacal animals do not relate to the zodiac as the area of the sky that extends approximately 8° north or south of the ecliptic, the apparent path of the Sun, the Moon, and visible planets across the celestial sphere's constellations, over the course of the year.
The Ox is the second of the 12-year periodic sequence (cycle) of animals which appear in the Chinese zodiac related to the Chinese calendar, and also appears in related calendar systems. The Chinese term translated here as ox is in Chinese niú , a word generally referring to cows, bulls, or neutered types of the bovine family, such as common cattle or water buffalo. The zodiacal ox may be construed as male, female, neutered, hermaphroditic, and either singular or plural. The Year of the Ox is also denoted by the Earthly Branch symbol chǒu. The term "zodiac" ultimately derives from an Ancient Greek term referring to a "circle of little animals". There are also a yearly month of the ox and a daily hour of the ox. Years of the oxen (cows) are cyclically differentiated by correlation to the Heavenly Stems cycle, resulting in a repeating cycle of five years of the ox/cow, each ox/cow year also being associated with one of the Chinese wǔxíng, also known as the "five elements", or "phases": the "Five Phases" being Fire, Water, Wood, Metal, and Earth. The Year of the Ox follows after the Year of the Rat which happened in 2020 and is then followed by the Year of the Tiger, which happened in 2022.
The Rat or Mouse is the first of the repeating 12-year cycle of animals which appear in the Chinese zodiac, constituting part of the Chinese calendar system. The Year of the Rat in standard Chinese is Chinese: 鼠年; pinyin: shǔnián. The rat is associated with the first branch of the Earthly Branch symbol 子 (zǐ), which starts a repeating cycle of twelve years. The Chinese word shǔ refers to various small rodents (Muroidea), such as rats and mice. The term "zodiac" ultimately derives from an Ancient Greek term referring to a "circle of little animals". There are also a yearly month of the rat and a daily hour of the rat. Years of the rat are cyclically differentiated by correlation to the Heavenly Stems cycle, resulting in a repeating cycle of five years of the rat, each rat year also being associated with one of the Chinese wu xing, also known as the "five elements", or "phases": the "Five Phases" being Fire, Water, Wood, Metal, and Earth.
Tianlong is a flying dragon in Chinese mythology, a star in Chinese astrology, and a proper name.
The sexagenary cycle, also known as the Stems-and-Branches or ganzhi, is a cycle of sixty terms, each corresponding to one year, thus a total of sixty years for one cycle, historically used for recording time in China and the rest of the East Asian cultural sphere. It appears as a means of recording days in the first Chinese written texts, the Shang oracle bones of the late second millennium BC. Its use to record years began around the middle of the 3rd century BC. The cycle and its variations have been an important part of the traditional calendrical systems in Chinese-influenced Asian states and territories, particularly those of Japan, Korea, and Vietnam, with the old Chinese system still in use in Taiwan, and to a lesser extent, in Mainland China.
Tai Sui is a Chinese term for the stars directly opposite the planet Jupiter during its roughly 12-year orbital cycle. Personified as deities, they are important features of Chinese astrology, Feng Shui, Taoism, and Chinese Buddhism to a lesser extent.
The Department of Divinities, also known as the Department of Shinto Affairs, Department of Rites, Department of Worship, as well as Council of Divinities, was a Japanese Imperial bureaucracy established in the 8th century, as part of the ritsuryō reforms. It was first consolidated under Taihō Code which established the Department of Divinities and Daijō-kan, the Council of State. However, the department and Daijō-kan made its first appearance in the Asuka Kiyomihara Code.
The Four Pillars of Destiny, as known as "Ba-Zi", which means "eight characters" or "eight words" in Chinese, is a Chinese astrological concept that a person's destiny or fate can be divined by the two sexagenary cycle characters assigned to their birth year, month, day, and hour. This type of cosmological astrology is also widely used in both South Korea and Japan.
In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. Although there are two such intersections, the equinox associated with the Sun's ascending node is used as the conventional origin of celestial coordinate systems and referred to simply as "the equinox". In contrast to the common usage of spring/vernal and autumnal equinoxes, the celestial coordinate system equinox is a direction in space rather than a moment in time.
In Chinese astrology, the symbolic stars, also translated as star spirits or calendar spirits, represent beneficial and baleful influences believed to be present during particular times, typically in relation to the specific positions and interactions of the heavenly stems and earthly branches used in traditional Chinese timekeeping and the sexagenary cycle.
Wen Wang Gua is a method of interpreting the results of I Ching divination that was first described in writing by Jing Fang in Han dynasty China. It is based on correlating trigrams to the Celestial Stems and Earthly Branches of the Chinese calendar, and then using the stem and branch elements to interpret the lines of the trigrams and hexagrams of the I Ching. The method is popular in South East Asia. It is known by various names: refers to the fact that it interprets the meaning of six symbols; the Najia method, indicates its logic of elemental values derived from the Chinese calendar; Wu Xing Yi ; or Wen Wang Ke.