Chinese Astrology 101: Although there are more complex calculations and analyses involved, this is a quick and simple way to find out if a certain day will be lucky or unlucky for you.
To recap from the “Chinese time” post, the Chinese believe that qi (or “chi” depending on the Chinese dialect) is a form of energy that encompasses all living things, or even natural elements/minerals. Manmade products such as plastic are not natural, and therefore do not have qi (so is the consensus thus far, but that may change in the future if more scientists get interested in feng shui and start studying it “scientifically” 
—on another note, scientists have recently found an invisible substance referred to as “gray matter,” which could possibly be qi… hmmmm).
Qi is energy coming from heaven and the earth. Ancient astrologists were able to discover 10 heavenly energies (which they called heavenly stems) and 12 earthly energies (called earthly branches). They believed that these energies were present each hour, day, month and year. Their characteristics and interactions could be studied and used to foretell the future.
The year 2008 is ruled by the stem “wu” and the branch “zi,” making this a “wu zi” year. (It is always in this order: stem first, then branch.) May is “ding si” month (“ding” is the stem and “si” is the branch). Today, May 15, is a “yi mao” day. Refer to the “Chinese time” post for the full listing of stems and branches (sorry to confuse you, but I listed the branches first and then the stems later).
In time, laypeople dropped the stem designation and referred to only the 12 earthly branches to tell time. Through folk legend, each branch was given an animal name. So, zi became rat, chou – ox, yin – tiger, mao – rabbit, chen – dragon, si – snake, wu – horse, wei – goat, shen – monkey, you – rooster, xu – dog, and hai – pig.
People could relate easier to the animals and their characteristics. For example, instead of having to memorize what the branch “zi” stood for, they could use the term “rat,” which in ancient times was an animal respected for its cunning, charm and wit (unlike today’s view of a rat as being a filthy, disease-carrying vermin 
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It is believed that when you are born, you are bombarded, enveloped and infused by the energies present during that hour (the Chinese don’t have hours, they use two-hour intervals), day, month and year. The stem-branch combination of the hour in which you are born, along with the stem-branch of the day you were born, the stem-branch of the month and the stem-branch of the year form the basis of your astrological chart.
Called the four pillars—hour pillar, day pillar, month pillar and year pillar, these 8 characters (a stem and branch for each pillar) can be read and analyzed to predict your luck, fortune, family and career situation, and destiny. An expert Chinese astrologer can calculate your future and analyze your good and bad times according to whether your birth chart clashes with the prevailing chart during a certain time period.
As this is a rather complicated analysis and protected information, laypeople were taught to simply analyze their year branch—or animal sign—with the day, month or year’s animal sign. (You could analyze hour by hour, but that would be very OCD —unless you want to predict an important event.)
Part 2 will explain how to tell if you’ll be having a bad day. To be continued…
