Yin is the third of the twelve Earthly Branches (dizhi), distinct from the yin of the yin-yang polarity, which is a different word. Its zodiac animal is the Tiger, its element is Wood, its direction is east-northeast, and its double-hour runs from 3 to 5 am, the hour before daybreak. As one of the twelve branches it combines with the ten Heavenly Stems to form the sexagenary cycle of sixty that numbers years, months, days, and double-hours. In the traditional calendar the branch Yin is associated with the first month of the lunar year in the common reckoning. These are the conventions of the Chinese calendrical and cosmological tradition, in which the twelve branches order the twelve-year animal cycle, the months, and the twelve two-hour periods of the day.
Yin is the third Earthly Branch, corresponding to the Tiger in the twelve-animal cycle, and to the double hour from 3 am to 5 am, the pre-dawn hours. Its dominant hidden stem is Jia, giving it the Wood phase, with Bing and Wu present as secondary hidden stems. Because the traditional Chinese calendar's civil and agricultural month count begins with Yin rather than with Zi, the first lunar month of the year is called the month of Yin, a convention that has held since the Han dynasty's adoption of the Xia calendar's month ordering, even though Zi retains its place as the first branch of the twelve and the first double hour of the day. Note that the branch Yin, the Tiger, is an unrelated homophone of yin the polarity opposite yang; the two are written with entirely different characters.