Liu Xin

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For the Western Han Dynasty emperor named Liu Xin, see Emperor Ai of Han; not to be confused with Emperor Guangwu of Han, also named Liu Xiu.

Liu Xin (traditional Chinese: 劉歆; simplified Chinese: 刘歆; Wade-Giles: Liu Hsin) (?? – 23), later changed name to Liu Xiu (劉秀), courtesy name Zijun (子駿), was a Chinese astronomer and historian during the Xin Dynasty. The son of the Confucian scholar Liu Xiang, he created a new astronomical system, called "Triple Concordance". He published this system in the year 8 as section of his textbook. In it he provided the following periods:

Therefore his number of days in one year was 365.25016, which is 11 minutes longer than the current value.

Liu created a catalog of 1080 stars, where he used the scale of 6 magnitudes. He also calculated periods for planets.

For centuries before the reign of Wang Mang (r. 9–23) the Chinese had used the value of 3 for their calculation of pi.[1] Between the years 1 and 5, while working for the de facto head of state Wang Mang, Liu Xin was the first to give a more accurate calculation of pi at 3.154, although the exact method he used to reach this figure is unknown.[2] However, the ancient record of Liu Xin's 'Jia Liang Hu' standard is still preserved in Beijing, which Joseph Needham quotes below with modern references for archaic units (Wade-Giles spelling):[2]

The standardised chia liang hu (has) a square with each side 1 chhih (foot) long, and outside it a circle. The distance from each corner of the square to the circle (thiao phang) is 9 li 5 hao. The area of the circle (mu) is 162 (square) tshun (inches), the depth 1 chhih (foot), and the volume (of the whole) 1620 (cubic) tshun (inches).[2]

Later mathematicians such as Zhang Heng (78–139) and Liu Hui (fl. 3rd century) would improve Liu's calculation for pi approximate to the standard of pi used in modern times.[3]

A crater on Mars was named in his honor.

[edit] Notes

  1. ^ Needham, Volume 3, 99.
  2. ^ a b c Needham, Volume 3, 100.
  3. ^ Needham, Volume 3, 100–101.

[edit] References

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  • Bin, Hansheng, "Liu Xin". Encyclopedia of China (Philosophy Edition), 1st ed.
  • Needham, Joseph (1986). Science and Civilization in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth. Taipei: Caves Books, Ltd.


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