A Chinese astrology chart is composed of both "Celestial" or "Heavenly Stems" and "Earthly Branches". Heavenly Stems are denoted by one of the Five Elements (either yin or yang), whilst the Earthly Branches are more commonly known as the animals of the Chinese zodiac.
They are arranged in four columns or "pillars" and as there are two parts to each column, the Four Pillars of Destiny are traditionally known as Ba Zi, meaning "Eight Characters".
There are ten Heavenly Stems and twelve Earthly Branches or animals and they are used not only to construct a Chinese horoscope, but also in the practice of feng shui to indicate direction on a traditional Chinese compass or Luo Pan.
The Ten Heavenly Stems
The ten Heavenly Stems represent heaven's chi and "providence". They are arranged according to the Five Elements and subdivided into yang and yin polarities. The sequence begins with yang wood (Jia), yin wood (Yi), yang fire (Bing), yin fire (Ding), yang earth (Wu), yin earth (Ji), yang metal (Geng), yin metal (Xin), yang water (Ren), and ends with yin water (Gui).
The Twelve Earthly Branches
Below your Heavenly Stems are your "Earthly Branches" or what are more commonly known as the animals of the Chinese Zodiac. They represent Earth Luck, meaning nature or destiny and have the ability to get you in the right place and, with heaven luck, at the right time. They are also arranged according to the Five Elements, Yin and Yang polarities and follow the four seasons. The Earthly Branches comprise the Chinese zodiac signs of Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Sheep, Monkey, Rooster, Dog and Pig and should always be written in this order.
The Earthly Branches show the rise and fall of qi throughout a year and as there are twelve zodiac signs and twelve months in a year, each sign is fixed. The Chinese use double hours so each animal sign is also associated with a two hour period of a day.