24 Seasonal Segments 二十四节气

The earliest calendars can be traced to the Neolithic period, but it is only with the beginning of the dynastic period that calendars were standardized and formalized. From the Shang Dynasty (1523-1027 BC) to the Warring States Period (770-221 BC) there was continuous improvement in observation and thus the calendar improved. All of the calendars were based on the average motion of the moon and measured a month as starting and ending with the new moon. Oracle bones show that during the Shang Dynasty people used a year of 365 days and a lunar month of about 29 or 30 days. It was during the Warring States Period that the 24 Seasonal Segments (二十四节气 èrshísì jiéqì) were incorporated into the calendar.

The sky is divided into 24 segments or jiéqì (节气) based on the seasons of the year. The earliest calendars assumed that the motion of the sun was constant and divided the year into 24 segments with equal numbers of days. This method is called píngqì (平气). Because the motion of the sun is not consistent, this was found to be inaccurate. The calendar then changed to a method where the ecliptic (the path of the sun as seen from earth) was divided into 24 equal parts of 15 degrees. This method is called dìngqì (定气). Calendars from the Warring States Period through the Ming Dynasty used the pingqi method in their designs and only changed to the more accurate dingqi method during the Qing Dynasty.

The average lunar month is a little more than 29 and 1/2 days. It is the half day that is a problem. The solution was to have both short (29 days) and long months (30 days). The procedure works for a short time but eventually gets out of step with the new moon because the lunar month is slightly longer than 29.5 days. To correct that, periodically a double long month would be added to the calendar to bring the beginning of the month back to the new moon. The leap concept was also used to bring the calendar back to agreement with the year. An average of 29.5 days in 12 months only gives you 354 days in a year. Every few years, an extra month called an intercalary month would be added to make up the days needed to keep the solstices and equinoxes consistent with the seasons.

During the Eastern Han Dynasty (25-220 AD), Jiǎ Kuí 贾逵 observed that the motion of the moon was actually inconsistent, but he continued to use the pingqi method of calculation in his Sì Fèn calendar (四分历). In 223 AD Kàn Zé (阚泽) used the dingqi method to predict eclipses but still based his Qian Xiang calendar on the pingqi method. Subsequently, several calendars were proposed (from the Yuan Jia calendar in 445 AD through the Wu Yin calendar in 619 AD) that incorporated the dingqi method. In each case the imperial court refused the innovation because the procedure would include more than two long months in a sequence.

It is amazing that a culture that regularly required its astrologers to rewrite the calendar would hold on so tightly to the simple rule of the pingqi calendars, "Never more than two long months in a row," but they did. The relationship between our view of stability and the mythology we create around time is deep seated. We happily deal with uneven months and leap years, but if it were seriously proposed that we straighten the whole thing out, there would be riots in the streets as there were when the Gregorian calendar was introduced. It is not logical that we cling to something that is just a concept, but we do. As a consequence, calendars could be "reset", but they had to use the same rules.

Although future astronomers continued to use the dingqi calculation to develop their calendars and to make observations after the Qian Xian calendar, it wasn't until the Qing Dynasty that it was actually built into the calendar. All of the earlier calendars were based on the pingqi method.

Below is a table of the 24 seasonal segments shown in the picture above. They are based on the idea of predicting the seasonal variation using the moon's motion to measure the time it will take for the earth to return to a certain position (the solstices and equinoxes) in relation to the sun. Thus, the Chinese calendar is a lunisolar model.

Below that is a partial list of some of the calendars in Chinese history. A few will be discussed in greater depth on subsequent pages.

1 Li Chun 立 春
2 Yu Shui 雨 水
3 Jing Zhe 惊 蛰
4 Chun Fen 春 分
5 Qing Ming 清 明

6 Gu Yu 谷 雨
7 Li Xia 立 夏
8 Xiao Man 小 满
9 Mang Zhong 芒 种
10 Xia Shi 夏 至
11 Xiao Shu 小 暑
12 Da Shu 大 暑
13 Li Qiu 立 秋
14 Chu Shu 处 暑
15 Bai Lu 白 露
16 Qiu Fen 秋 分
17 Han Lu 寒 露
18 Shuang Jiang 霜 降
19 Li Dong 立 冬
20 Xiao Xue 小 雪
21 Da Xue 大 雪
22 Dong Zhi 冬 至
23 Xiao Han 小 寒
24 Da Han 大 寒
Beginning of spring (Spring Festival)
Rain water
Waking of insects
Spring equinox (March 21)
Pure brightness
Grain rain
Beginning of summer
Grain full
Grain in ear
Summer solstice (June 22)
Slight heat

Great heat
Beginning of autumn
Limit of heat
White dew
Autumnal equinox (September 23)
Cold dew
Descent of Frost
Beginning of winter
Slight snow
Great snow
Winter solstice (December 22)
Slight cold
Great cold

A Minor Sample of the 102 Calendars in Chinese History
Calendar 汉字 Year Astronomer 汉字 Dynasty Span Notes
Xià Xiǎo Zhèng 夏小正 16th
Xia 2070-1600 BC Divided the year into 12 months, comments on agriculture and weather observations
Lǔ lì 鲁历       Warring States 770-221 BC Pingqi method developed in Warring States
Zhōu lì 周历       Warring States 770-221 BC Pingqi method developed in Warring States
Yīn lì 殷历       Warring States 770-221 BC Pingqi method developed in Warring States
Xià lì 夏历       Warring States 770-221 BC Pingqi method developed in Warring States
Zhuān xū lì 颛顼历       Warring States 770-221 BC Pingqi method developed in Warring States
Huángdi4 lì 黄帝历       Warring States 770-221 BC Pingqi method developed in Warring States
Sì Fèn 四分历 85 AD Jiǎ Kuí 贾逵 Eastern Han 25-220 AD Discovered motion of the moon was inconsistent, based calendar on pingqi
Qián Xiàng 乾象历 223 AD Kàn Zé 阚泽 Three Kingdoms 220-280 AD Dingqi used to calculate eclipses but based calendar on pingqi
Yuán Jiā 元嘉
445 AD Hé Chéngtiān 何承天 Northern and
386-589 AD Using dingqi found that could have strings of 3 and 4 long or short months - not implemented due to political constraints
      Zhāng Zǐxìn 张子信 Northern and
386-589 AD Discovered inconsistent speed of the sun
Dà Míng 大明历 510 AD Zǔ Chōngzhī 祖冲之 Northern and
386-589 AD Measured precession of the earth's axis - sui cha (岁差)
Wǔpíng 武平历 576 AD Líu Xiàosūn 刘孝孙 Sui 586-618 AD Included a correction for the Sun's variable movement and solar center - not an official court calendar
Kāi Huáng 开皇 589 AD Zhāng Bīn 张宾 Sui 586-618 AD Inferior calendar written by a monk who was not an astronomer which replaced the Da Ming and ignored precession and the changing solstice point
Dà 大业历 596 or 597 AD Zhāng Zhòuxuán 张胄玄 Sui 586-618 AD Included a linear interpolation to estimate the Sun's changing speed
Huáng Jí 皇极 600 AD Líu Zhuō 刘焯 Sui 586-618 AD Discussed inconsistent speed of the sun, but thought the changes were sudden
Wù Yín 戊寅历 619 AD Fù Rénjūn 傅仁均 Tang 618-907 AD Dingqi showed string of 4 long months, so again used pingqi - (Fu Renjun also worked during the previous Sui Dynasty)
Lín Dé 麟得 665 AD     Tang 618-907 AD Dingqi in the form of dingshuo became the common method for calculation - but still not the base of the calendar
Dà Yǎn 大衍历 729 AD Sēng Yī Xíng 僧一行 Tang 618-907 AD Corrected Zhāng Zhòuxuán and Líu Zhuō 's measurement of solar speed. Determined the actual movement of the Sun and used it to calculate eclipses but not in calendar. Still used pingqi
Fútiān 符天历 780 AD Cáo Shìwéi 曹士为 Tang 618-907 AD Parabolic interpolation for solar motion
Qīntiān 天历 956 AD Wáng Pǔ 王朴 Five Dynasties
and Ten Kingdoms
907-979 AD Used Yixing's meridian line to create a new algorithm of the Sun's shadow.
Shòu Shí 授时历 1281 AD Guō Shǒujìng 郭守敬 Yuan 1279-1368 AD Refined the measurement of the precession of the earth's rotation
Shí Xiàn 时宪历 1645 AD Adam Schall von Bell 汤若望 Qing 1645-1911 AD Ding qi and procession measures implemented in the calendar. Added calculation of Changed day from 12 hours (时辰) with 100 quarters to 24 hours and 96 quarters of 15 minutes. Added time zones for calculation of dawn, dusk and jie qi (seasonal segments), jie qi set at 15 degrees of the ecliptic.

Last update: May 2007
© Marilyn Shea, 2007