In ancient times it was 12. According to Zhao Wei's literature "Mandarin in Four Years", "Twelve years, one year is a period." This means that Jupiter takes about 12 years to orbit the sun. This is ancient times.

Chronology refers to accurately recording the time of historical phenomena in words. In five thousand years in China, writing appeared very early, and some events were recorded. However, even in the middle of the Western Zhou Dynasty, no time was recorded.

In order to solve this situation, Sima Qian clearly marked the major historical events that occurred in and after the first year of the Western Zhou Dynasty in Historical Records according to the information left by predecessors. The first year of the Republic is 84 BC1year. It was also from this year that the history of our country began to have an exact date.

annual report

In ancient China, the chronology was mainly realized by "heavenly stems" and "earthly branches". Characterized in that:

A, take one from the heavenly stems and one from the earthly branches to form a Gregorian calendar year, such as "Wu Jianian" and "Wuxu Year".

B, heavenly stems and earthly branches combination is always odd to odd, even to even, it is impossible to start with odd to even combination.

C, 60-year cycle, cycle after cycle.