Star Catalogue and Star Atlas

     Astronomy emerged quite early in ancient China. On some relics from the Neolithic Period there were astronomical signs and symbols. Sima Qian (c.145BC or 135BC-?), the great historian of the Western Han Dynasty, writes in his Shi Ji (Historical Records): Emperor Huangdi made observations of stars and worked out a calendar. He established the five elements of metal, wood, water, fire and earth, and understood their correlations, and he solved the problems of leap months and leap days in the calendar. He divided all things on earth under the heaven and the God into five groups, and brought about their orderly operations, free from disturbances and confusion.

Therefore the people believed in his rule, and the God praised his wisdom. He showed high respect to the people and the God, though they were quite different. As a result the people had the blessing of the heaven, and enjoyed an affluent life.

    This sowed the seed of the great concept of "integration of nature and man" and formed the ideological basis for astronomical undertakings. Soon after Emperor Huangdi, a post of Huozheng was established to take charge of astronomical and calendrical affairs, who was to make close observations of the Mars, so as to direct farming activities according to the positions of the planet. The duties of ancient officials in charge of astronomical affairs were to observe the movements of the sun, the moon and stars, forecast solar and lunar eclipses, determine the times of the solar terms, and work out calendars. With diligence, wisdom and perseverance, they made great contributions to astronomical observations and formulation of

calendars in ancient China.

    Gan De from the state of Qi and Shi Shen from the state of Wei were both royal astronomers. Shi Shen was the author of Tzanwen (Astronomy) in eight volumes, and Gan De also wrote an eight- volume Tianwen Xingzhan (Astronomical Observations of Stars). But both of their works have long been lost. In later years other writers collected excerpts from the two works that were quoted in other books, and compiled them into a book known as Gan Shi XingIing (Gan's and Shi's Classics on Stars). Both of them recorded a number of fixed stars, including their names and positions, but some of them overlapped. In the Three Kingdoms period astronomer Chen Zhuo put together all the fixed stars recorded by Gan De, Shi Shen and another astronomer Wu Xian, and divided them into 283 groups. All the 1,464 fixed stars were marked in a star map in different colors. Later astronomers used the map to work out a star atlas and a celestial sphere. In Gan's and Shi's Classics on Stars, 120 groups of 815 stars were attributed to Shi Shen, and 146 groups of 687 stars to Gan De.

    What is most valuable is that Shi Shen provided values of the coordinates of the 120 standard stars in 120 groups of stars, including their equatorial coordinates. The coordinates of the twenty-eight lunar constellations were expressed in the ascensional differences of their representative stars as arranged along the equator from west to east, and the angle between the fixed star and the celestial pole. As for other fixed stars in the constellations, their coordinates were the ascensional differences between them and the representative star, and the angles between them and the celestial pole. This shows Shi Shen's star catalogue adopted the equatorial coordinate system, or the right ascension and the declination to show the position of any celestial body on the celestial sphere. Shi Shen's star catalogue was completely expressed in numerals.

The adoption of the equatorial coordinate system was a unique contribution by ancient Chinese to world astronomy, as ancient astronomers in the West all used the ecliptic coordinate system to mark the positions of fixed stars. Astronomers in ancient Greece, from the time'of China's Warring States Period till the 16'h to 17'h centuries, used the ecliptic coordinate system inherited from Babylon. The combination of the equatorial coordinate system and the ecliptic coordinate system helps to improve the accuracy of astronomical observations and records. The astronomical achievements of Shi Shen and Gan De were all recorded in Kaiyuan Xingzhan the Kaiyuan Star Observations) from the Tang Dynasty. Although Shi Shen's star observations as seen in the Tang publication had been improved in several hundred years since his time, his star catalogue is nevertheless one of the earliest in the world and possesses high scientific values. Quite a few figures in the star catalogue were the results of observations made in the Warring States Period, which proved that Shi Shen had used angular surveying devices to determine the positions of celestial bodies in the equatorial coordinate system.

This in turn shows that Chinese astronomers in the Warring States Period led the world in astronomy and the making of astronomical instruments. Shi Shen and Gan De had another unique achievement: they divided the celestial sphere into 365 1/, degrees; as a tropical year has 365 1/, days, therefore each day the sun moves one degree on the celestial sphere. Yet in the West most ancient astronomers adopted the Babylon division, dividing the celestial sphere into 360 degrees. Shi and Gan also made fairly accurate observations of the five major planets. Both of them noted that the sidereal period of Jupiter was 12 years (compared with the exact value of 11.86 years). Shi Shen also found in observations that the syndic period of Jupiter was 400 days (compared with the exact value of 398.9 days), the syndic period of Venus was 587.25 days (compared with the exact value of 583.9 days), and the syndic period of Mercury. Was 136 days (compared with the exact value of 115.9 days).