SEXAGENARY CYCLE

The Chinese 'sexagenary cycle' () is a cyclic numeral system of 60 combinations of the two basic cycles, the ten Heavenly Stems (天干; tiāngān) and the twelve Earthly Branches (地支; dìzhī). These have been traditionally used as a means of numbering days and years, not only in China but also in other East Asian nations like Japan, Korea, and Vietnam. It is also an important part of Chinese astrology.

Overview

The cycle was used in China since the second millennium BC (it has been found on Shang dynasty oracle bones), as a means of ''naming'' days (just as we use the days in the week). This use of the cycle for days is attested throughout the Zhou dynasty. For instance, most entries in the Spring and Autumn Annals use this system.
Its use for recording years is more recent. It became widespread in the Western Han Dynasty (202 BC- 8 AD), and might have began in the late Warring States period. According to ''Nihon shoki'', the calendar was transmitted to Japan in 553. But it was not until the Suiko era around 602 that the calendar was used for politics.
The calendar is calculated by combining the and . These two sets of terms were used to enumerate years of the civil calendar. Combining the series form a greater cycle of 60 terms, as the least common multiple of 10 and 12 is 60. The first term is formed by adding the first stem to the first branch, then the second stem to the second branch, and so on. If you start with , so the 61st year would also be kinoe-ne. This was how the tradition of celebrating began. This counting system employing things of nature and animals create many myths, and people of Japan today still consider the good and bad luck of certain days and years.
The year 604, when the Japanese officially adopted the Chinese calendar, was the first year of the cycle. The year 1984 began the present cycle, and 2044 will begin another.

Ten Heavenly Stems

	Heavenly Stem	Chinese name (Mandarin pron. in pinyin)	Japanese name		Korean name		Vietnamese name	Yin Yang	Element
	Heavenly Stem	Chinese name (Mandarin pron. in pinyin)	Onyomi	Kunyomi with corresponding kanji	Romanized	Hangul	Vietnamese name	Yin Yang	Element
1	甲	jiǎ	kō	kinoe (木の兄)	gap	갑	giáp	yang	wood
2	乙	yǐ	otsu	kinoto (木の弟)	eul	을	ất	yin	wood
3	丙	bǐng	hei	hinoe (火の兄)	byeong	병	bính	yang	fire
4	丁	dīng	tei	hinoto (火の弟)	jeong	정	đinh	yin	fire
5	戊	wù	bo	tsuchinoe (土の兄)	mu	무	mậu	yang	earth
6	己	jǐ	ki	tsuchinoto (土の弟)	gi	기	kỷ	yin	earth
7	庚	gēng	kō	kanoe (金の兄)	gyeong	경	canh	yang	metal
8	辛	xīn	shin	kanoto (金の弟)	shin	신	tân	yin	metal
9	壬	rén	jin	mizunoe (水の兄)	im	임	nhâm	yang	water
10	癸	guǐ	ki	mizunoto (水の弟)	gye	계	quý	yin	water

Twelve Earthly Branches

	Earthly Branch	Chinese name (Mandarin pron. in pinyin)	Japanese name		Korean name		Vietnamese name	Chinese zodiac	Corresponding hours
	Earthly Branch	Chinese name (Mandarin pron. in pinyin)	Onyomi	Kunyomi	Romanized	Hangul	Vietnamese name	Chinese zodiac	Corresponding hours
1	子	zǐ	shi	ne	ja	자	tý	Rat (鼠)	11 p.m. to 1 a.m.
2	丑	chǒu	chū	ushi	chuk	축	sửu	Ox/Cow/Bull (牛)	1 to 3 a.m.
3	寅	yín	in	tora	in	인	dần	Tiger (虎)	3 to 5 a.m.
4	卯	mǎo	bō	u	myo	묘	mẹo/mão	Rabbit/Hare ★ (兔)	5 to 7 a.m.
5	辰	chén	shin	tatsu	jin	진	thìn	Dragon (龍)	7 to 9 a.m.
6	巳	sì	shi	mi	sa	사	tỵ	Snake (蛇)	9 to 11 a.m.
7	午	wǔ	go	uma	o	오	ngọ	Horse (馬)	11 a.m. to 1 p.m.
8	未	wèi	mi or bi	hitsuji	mi	미	mùi	Sheep/Goat (羊)	1 to 3 p.m.
9	申	shēn	shin	saru	shin	신	thân	Monkey (猴)	3 to 5 p.m.
10	酉	yǒu	yū	tori	yu	유	dậu	Chicken/Rooster (雞)	5 to 7 p.m.
11	戌	xū	jutsu	inu	sul	술	tuất	Dog (狗)	7 to 9 p.m.
12	亥	hài	gai	i	hae	해	hợi	Pig/Boar (豬)	9 to 11 p.m.

★ The names of several animals can be translated into English in several different ways. The Vietnamese Earthly Branches use Cat instead of Rabbit/Hare.
In a traditional story of the twelve animals, the cat and rat were once good friends, but the animals to be selected to represent the years included the cat but not the rat. These animals had to present themselves to be given the honour of representing the years in the cycle, and the cat asked the rat to wake him up before they had to go. The rat didn't do this, but instead went himself. When they came to cross a river, the rat jumped on the ox's back, and just before the ox got to the bank, the rat jumped off and was first in line. This is why the twelve animals are lead by the rat, and because the cat was cheated out of its rightful place, rats are forever sought out by cats for revenge.