ephemeris.com History of Astronomy — Ancient China
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History of Astronomy — Ancient China

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• Ancient China

In 213 B.C.E., Emperor Shih Huang Ti rose to power and gave the tragic order to collect all books in the kingdom and burn them. Today, we only have books that somehow survived this purge either by being hidden or reconstructed imperfectly from memory after Shih Huang Ti. The Chinese are thought to have had records possibly going back as far as 3000 B.C.E. before this destruction. Oracle bones dating to the Shang Dynasty (about 1800-1200 B.C.E.) also survive. They show a 19-year Moon cycle, and a 29 1/2-day lunar month. Days are grouped in 60-day cycles.

Astronomy flourished in the Han Dynasty, which began in 206 B.C.E. with the victory of Liu Bang over other armies. Slowly, the old knowledge was restored and spread again. Confucian beliefs were again introduced into the government over time. The Han Dynasty extended to southern Mongolia, into Korea and Vietnam, but north of Tibet.

In 2637 B.C.E., the legendary First Emperor Huan Ti (the "Yellow Emperor") instituted the calendar that survives in China to this day for festival dates. The calnedar has lunar months but the seasons are determined by the position of the stars. Like the calendars developed in ancient Mesopotamia, a regular year has 12 lunar months and an intercalary leap year has 13 lunar months. This is therefore a luni-solar calendar, able to track the seasons and at the same time divide the year into months. According to legend, the intercalary leap months were added by the Fourth Emperor, Emperor Yao. Unlike the Mesopotamian-derived calendards, a Chinese month begins at the New Moon, not the first crescent after a New Moon.

The 78th cycle began in the year -2636 + 78 (60), which is the year 1984. The year 2004 is the 21st year in the 78th cycle from the date the calendar was started. A New Year begins on the New Moon in the month when the Sun's longitude is 330°.

In 104 B.C.E., Emperor Wu of the Western Han Dynasty summoned a conference of astronomers to improve timekeeping. During this conference, a new rule was added to determining the months: the Winter Solstice date. Astronomers decided to track the solstices by measuring the shadow from an eight-foot bamboo stalk. From recorded observations, today we know these observations must have been made in the Hunan Province. The Emperor also declared at this time that a leap month would occur whenever the Sun did not move to a new zodiac sign. These rules of Emperor Wu, instituted in 104 B.C.E., still determine the Chinese Calendar to this day.

During and after Emperor Wu's conference, two astronomers were instrumental in improving calculations of time: Ssu-ma-Ch'ien and his assistant Lo-hsia-Hung. They used a bamboo stalk for measuring time during the day, and a water clock to measure time at night. Lo-hsia-Hung is thought to be the first Chinese astronomer to construct an armillary sphere, with 365.25 divisions, and rings for the Equator and the meridian. Several centuries later, another ring was added for the ecliptic.

Lo-hsia-Hung likened Heaven and Earth to a shell surrounding its yolk. He stated that the Earth's movement caused the seasons; "the Earth moves cconstantly but people do not know it; they are as persons in a closed boat; when it proceeds they do not perceive it." [Maspero, p. 336].

Chinese astronomy made rapid progress in the following centuries. In 25 C.E., Liu-Hsin produced a textbook that contained a section on astronomy. It stated that the Moon's phases (the synodic month) repeated every 29 43/81 days (just 23 seconds extra). It gave 235 synodic months in 19 years, and also gave 254 lunar sidereal months in 19 years. This was used to calculate the year as 365 385/1539 days. This is 365.25016 days, 11 minutes extra. The textbook reasoned that the Sun passes through the Moon's Nodes 23 times in 135 synodic months, so eclipses must return every (135/23) x (29 43/81) = 173 1/3 days, just 35 minutes extra. Planetary periods were given accurate to within about half a day or better.

In the first century C.E., China's expansion into Central Asia exposed Chinese astronomers to Hindu and Persian astronomical advances. Chinese documents mention astronomers from Near Asia visiting China in 164 C.E. Other Chinese documents mention the astronomer Ho-Tsheng-Tien learning astronomy from an Indian priest. This priest taught him, among other things, how to determine latitue from the meridian height of the Sun.

During the Tang Dynasty in 619 C.E., astronomers approximated the relative motions of the Sun and Moon with parabolas. This was more accurate than the Chaldean modified sawtooth progression, but not as accurate as sinusoidal curves. During the Qing Dynasty in 1645 C.E., the Constant Conformity calendar was instituted. This calendar adopted the positions of the Sun and Moon from more accurate formulas brought to China by Jesuit missionaries.

In June of 1054 C.E., Chinese astronomers recorded a "new star" in Taurus. The star was visible in the daytime for two years, then disappeared. Today we know that they observed the supernova explosion that became the Crab Nebula.

The modern Chinese Calendar typically calculates the New Moon at 120° East Longitude (approximately the position of Mainland China's East Coast), but this can vary by location. Also, some communities number the years from 2697 B.C.E., sixty years earlier.

The years follow a 60 year cycle, in five groups of 12 years. Each of the 12 years is named after an animal. According to tradition, Gautama Buddha called the animals of the Earth to him before he left his body. Only twelve came, and the years are named in the order in which the animals arrived. The years in this cycle are: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Sheep, Monkey, Rooster, Dog, and Boar. 2003 was the Year of the Sheep. 2004 is the Year of the Monkey, and so on. The five qualities are Wood, Fire, Earth, Metal, and Water. They proceed along with the animal for a year. For example, if one year is the Year of the Wood Rat, the next is the Year of the Fire Ox, next the Year of the Earth Tiger, and so on.

Because the current cycle began in 1984, the year 1984 is the Year of the Wood Rat. Twenty years later, the year 2004 is the Year of the Wood Monkey. The Chinese New Year in 2004 began on 22 January.

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