BaZi, “八 Ba” means eight and “子 Zi” means character. The eight Chinese characters are derived from the Xia/ HSIA farming calendar which represent the year, month, day, hour and indicates beside of the season’s transition the planetary cycles at given time.
The HSIA calendar has a 60-years cycle and consists of two characters for any given time. The upper characters are called 天干 10 Celestial/ Heavenly Stems and represent the five planets dominance and impact with its polarity on the year, month, day and hour.
The lower characters are called 地支 12 Terrestrial/ Earthly Branches and represent the Earths position in relation to other planets.
The planet Jupiter, which is the biggest planet in our solar system completes its cycle around the sun every twelve years, its magnetic field is about twenty times stronger than Earth's and it’s been believed that it has high impact on our nature. Therefore the “Earthly Branch” of the year or in short the year branch indicates planet Jupiter’s position around the sun.
The Month-Branch indicates the Earths position around the Sun and the transition of seasons. The beginning or completion of the month is not necessarily the first day of the Month.
The Day-Branch indicates the moons position/ phases around the Earth. Apparently the day in month, or in another words, the moon's position around the earth has the highest impact on our nature.
The Hour-Branch indicates the Earth phase rotation on its own axis. Each Chinese Hour consists of two hours; the day is divided into 12 instead of 24 hours.
Chinese call the five closest planets in our solar system “Elements”, namely Wood for Jupiter, Fire for Mars, Earth for Saturn, Metal for Venus and Water for Mercury. Each of the five Planets/Elements has its own polarity, the positive polarity (+) is called Yang and the negative polarity (-) is called Ying.
A plotted Chart from HSIA calendar with the eight characters is also known as “BaZi” Ming Pan (Eight characters of life) or 四柱 Four Pillars of Destiny.