Chinese Lunar Calendar中国阴历

   Although China has adopted the Gregorian calendar① in common with most other countries in the world for official and business purposes, the traditional Chinese calendar continues to define the dates of festivals and is used for Chinese Zodiac. The calendar has a very long history going back to the Xia and Shang dynasties. It is based on a unique combination of astronomy and geography through observation and exploration. Thus, in essence, it is a combined solar/lunar calendar. It is also referred to as the Lunar, Yin, Xia or the old Chinese calendar.   

   Following its creation in the Xia Dynasty, succeeding reigns continued to use the calendar but modified it from time to time. In the Shang Dynasty, officials were appointed to bear the sole task of observing and recording the changes in the heavens. During this period, people used the lunisolar calendar②, with an intercalary（闰） added to the end of certain years. In the Western Han Dynasty, Emperor Wu ordered the establishment of a new calendar－Taichu Calendar③, based on the old calendar. And the calendar was used in the next 200 years. Later, Zu Chongzhi worked out the Daming Calendar (大明历), taking into consideration the precession of the equinoxes④（分点岁差） for the first time in China. After observations and studies, Zu concluded that a year lasted exactly 365.24281481 days which was only 52 seconds different from the modern estimate. In the Tang Dynasty, famous monk Yi Xing compiled the Dayan Calendar(大衍历), the most comprehensive and thorough calendar in the Chinese history. The calendar had great influences as all the later ones were revised according to it before the introduction of the western calendar. In the Northern Song Dynasty, Shen Kuo worked out the 12 Qijie Calendar, discarding the intercalary（闰）and this is in line with the Gregorian Calendar. During the Yuan Dynasty, Guo Shoujing compiled the Shoushi(授时历) Calendar. He employed several methods of calculation to solve the main problems in the previous calendars. His calendar had 365.2425 days in a year, which was only 26 seconds different from the time it takes the earth to go around the sun. His achievement was 300 years earlier than the finalization of the modern calendar. With the founding of the Republic of China in 1912, the Gregorian calendar was introduced to China. 

   In the Chinese Lunar Calendar, one year is divided into 12 months and the months have either 29 or 30 days, always beginning on days of astronomical（天文的）new moons. So each year has 354 or 355 days. Each time the moon moves into line with the earth and the sun a new month begins and this is called “Chu Yi” or “Shuo Ri” (朔日) (the first day of a lunar month). The longest day of a year or Summer Solstice (夏至) falls on the 21st or 22nd of the sixth lunar month, and the shortest day is the Winter Solstice (冬至) on either 21, 22, or 23 of the twelfth lunar month. Using these two annual events the year was divided into in 24 equal parts, each forming the 24 solar terms. 

   To make the average length of the years equal to a tropical year（回归年）, an intercalary month is added every two or three years. As a result, an ordinary year（平年）has 12 months while a leap year(闰年) has 13 months. And an ordinary year has 354, or 355 days, and a leap year has 384 or 385 days.

   To decide when a leap month needs to be added to bring the lunar calendar in relation to the earth’s movement around the sun, the 24 solar terms are added. Most months will have solar terms and but in those instances where a month has only one, it will be repeated with 29 or 30 days the same as a normal month. This phenomenon can occur every two or three years.

  China is one of the first countries that see the emergence of astronomy(星象). The Chinese lunar calendar is closely related with the development of the astronomy. It also has links with natural sciences such as agriculture and solar terms, the four seasons and traditional festivals such as the Spring Festival. There are links also with the “Five Elements” of which the ancient Chinese believed the physical universe to be composed namely, metal, wood, water, fire and earth. 

                                                            Abridged and revised from                                      

                           http://www.chinaculture.org/library/2008-02/01/content_26219.htm

Notes:

①Gregorian calendar: 公历。公历的标准名称为格里高利历，是现在国际通用的历法，是一种阳历。阳历是太阳历的简称，这种历法与地球环绕太阳的周年运动有关，与月相无关。格里高利历为西方的历法，并非中国所创，故又名“西历”（是相对于中历而言）。

②lunisolar calendar: 阴阳历，在天文学中是指兼顾太阳、月亮与地球关系的一种历法。阴阳历以月亮绕地球一周为1个月，但设置闰月，使得一年的平均天数与回归年的天数相符，因此这种历法与月相相符，也与地球绕太阳周期运动相符合。夏历就是阴阳历的一种。

③Taichu Calendar: 《太初历》，是中国古代第一部比较完整的汉族历法，也是当时世界上最先进的历法。其法规定一回归年为一年，一朔望月为一月，所以又称八十一分律历。以夏历的正月为岁首。三统历第一次把二十四节气编入历法，以没有中气的月份为闰月。

④the precession of the equinoxes: 岁差，在天文学中是指一个天体的自转轴指向因为重力作用导致在空间中缓慢且连续的变化。例如，地球自转轴的方向逐渐漂移，追踪它摇摆的顶部，以大约26,000年的周期扫掠出一个圆锥（在占星学称为大年或柏拉图年）。