Liu Xin ( ) (ca. 46 BC – AD
23), later changed name to Liu Xiu (劉秀), courtesy name Zijun (子駿), was
a Chinese astronomer, historian,
and editor during the Xin Dynasty (AD
9–23). He was the son of Confucian scholar
Liu Xiang (77–6 BC) and an associate of
other prominent thinkers such as the philosopher
Huan Tan (d. 28 AD). Liu 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
magnitude. 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. 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. 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):
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).
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.
Although Liu Xin was originally a loyal partisan of Wang Mang,
after Wang's troops suffered defeat on
July
7,
23 at the
Battle of Kunyang, Liu Xin plotted with
others to overthrow Wang Mang. The plot was discovered, while all
the conspirators committed suicide or were executed.
A
crater on
Mars
was named in his honor.
See also
Notes
- Crespigny, 338.
- Needham, Volume 3, 99.
- Needham, Volume 3, 100.
- Needham, Volume 3, 100–101.
- Bielenstein, 247–248
References
- Bielenstein, Hans. (1986). "Wang Mang, the Restoration of the
Han Dynasty, and Later Han," in The Cambridge History of China:
Volume I: the Ch'in and Han Empires, 221 B.C. – A.D.
220. Edited by Denis Twitchett and Michael Loewe.
Cambridge: Cambridge University Press. ISBN 0521243270.
- Bin, Hansheng, "Liu Xin". Encyclopedia of China (Philosophy
Edition), 1st ed.
- Crespigny, Rafe de. (2007). A Biographical Dictionary of
Later Han to the Three Kingdoms (23-220 AD). Leiden:
Koninklijke Brill. ISBN 9004156054.
- Needham, Joseph (1986). Science and Civilization in China:
Volume 3, Mathematics and the Sciences of the Heavens and the
Earth. Taipei: Caves Books, Ltd.