This will be my second Year of the Monkey. In ancient China there were many ways of counting the years. From 365 BC the names of the 12 annual stations of Jupiter were used, but they were replaced by the the stations of Taisui, the God of Time, which was an invisible counter-orbital correlate of Jupiter.
The present method dates from the Qin dynasty, ie. around 200 BC, and uses the 12 animals, shengxiao, to create an association with the 12 Taisui and one of the 12 earthly branches, or dizhi. In 1912, the provisional president Sun Yat-sen decreed that from January 1st the new Republic would adopt the Gregorian calendar and the solar year.
But the old habits persist for the major traditional festivals such as the lunar New Year.