Wu is the seventh of the twelve Earthly Branches (dizhi), distinct from the fifth Heavenly Stem of the same romanisation. Its zodiac animal is the Horse, its element is Fire, its direction is due south, and its double-hour runs from 11 am to 1 pm, the hour of noon, when yang is at its height. 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. Standing opposite the midnight branch Zi, Wu marks the sun's zenith. 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 into which the day is divided.
Wu is the seventh Earthly Branch, corresponding to the Horse, and to the double hour from 11 am to 1 pm, midday, the branch's noon position mirroring Zi's midnight position exactly opposite it on the twelve-branch wheel. Its dominant hidden stem is Ding, giving it the Fire phase, with Ji present as a secondary hidden stem. Wu is a Yang-polarity branch, pairing only with Jia, Bing, Wu, Geng or Ren within the sexagenary cycle, and it governs the fifth lunar month, the height of summer. The branch Wu, the Horse, is an unrelated homophone of Wu the fifth Heavenly Stem (Yang Earth); the two share a romanised spelling but are written with different characters and belong to different halves of the sexagenary system. In BaZi astrology a chart with Wu prominent is read through the Horse's traditional associations of energy, sociability and restlessness, amplified by the Fire phase's own association with rapid, outward-moving activity.