Reference: The Oxford Companion to the Year - Bonnie Blackburn and
Leofranc Holford-Strevens. Pg 696-707
The Chinese calendar is a 19 year cycle. Seven of these 19 years have 13
months, and the rest have 12. Theres a whole heck of a lot more to it
than the 12 animals that you see on your placemat at your favorite
There is a cycle of 10 stems and 12 branches. Each stem has associated
with it an element (wood, fire, earth, metal, water) a yang (fir,
kindling, hill, weapons, waves) a yin (bamboo, lamp-flame, plain,
kettle, brooks) a cardinal point (east, south, centre, west, north)
and a planet (Jupiter, Mars, Saturn, Venus, Mercury).
Likewise, each branch has associated with it an animal, an element, a
double-hour, a compass point, and a sign of the zodiac.
Each of these various cycles are going on at the same time, and so
interact with each other to produce combinations of all of these
different components. And various combinations mean various things.
There are, of course, many folks that have more knowledge of how this
all works than I do. I just used to be a mathematician.
http://www.math.nus.edu.sg/aslaksen/calendar/chinese.shtml seems like
a good place to start, but there are many other very informative sites
on the net.