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祖冲之 Zu Chongzhi (AD 429-500) An early Chinese star of astronomy
By Zhang Ciyun |
May 15, 2011, Sunday
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Print Edition
Print Edition
One summer night more than 1,500 years ago, a Chinese boy was sitting in a courtyard and watching a full bright moon. He turned to his grandfather sitting next to him and asked: "Grandpa, why is the moon sometimes full and not at other times?"
The grandfather explained that the movement of the moon had its own rules, so it became full at a certain time every month. Then he asked the boy: "Are you interested in the moon and stars?" The boy answered enthusiastically: "Yes, very much."
The old man immediately stood up and went into the house. A few moments later, he returned with several books. He told the boy: "These are some classic books on astronomy. You may like to read them."
The boy spent much time devouring the books in the following months. He then decided to take astronomy as his career and eventually became one of the most outstanding mathematicians and astronomers in the world. His name was Zu Chongzhi.
The Zu family moved to today's Nanjing, capital of Jiangsu Province in eastern China, from the north to escape wars and political turmoil. Both Zu's grandfather and father served in the imperial court of Liu Song Dynasty (AD 420-479). His grandfather was an engineer in charge of construction and his father a technical consultant.
Under the emperor's patronage, the young Zu was sent to study at the Imperial Nanjing University and then the Imperial Institute. Later, he was assigned to work in an office in today's Zhenjiang in Jiangsu Province for the local governor.
During his study and research at those institutes, Zu first concentrated on calculating the value of pi. Thanks to his computation technique which was way ahead of its time, Zu was able to work out the numerical value of pi to be between 3.1415926 and 3.1415927. Zu obtained this extraordinary fraction more than 1,000 years before European scientists. And Zu's pi was later named by other scientists the Zu Chongzhi Fraction.
In AD 465, Zu created a new calendar, the Daming Calendar, for the imperial court. The new calendar was a great improvement over previous calendars and contained many discoveries that Zu had made in astronomy. For instance, Zu calculated the yearly difference based on the movement of the earth's axis in relation to the fixed stars. In other words, he measured the difference between the Sidereal Year and the Tropical Year.
Zu's measurement of 45 years 11 months per degree was rough compared with the difference of 70.7 years per degree as we know today. However, he was the first astronomer in the world to incorporate the measurement into a calendar.
In addition to his contributions to mathematics and astronomy, Zu also made great achievements as an engineer. One of his most outstanding feats is his reinvention of the South Pointing Chariot in AD 478.
Unlike a compass, which relies on magnetism to achieve the north-pointing effect, the South Pointing Chariot was based on complicated gear works to enable a fixed figurine on a chariot to constantly point south. The device was invented by a Chinese mechanical engineer called Ma Jun in AD 255, but later lost in history.
However, both Zu's recreation of the chariot and a comprehensive mathematical book entitled "The Method of Interpolation," which was co-authored by Zu and his son Zu Gengzhi, also a famous mathematician, failed to survive to the present day.
The grandfather explained that the movement of the moon had its own rules, so it became full at a certain time every month. Then he asked the boy: "Are you interested in the moon and stars?" The boy answered enthusiastically: "Yes, very much."
The old man immediately stood up and went into the house. A few moments later, he returned with several books. He told the boy: "These are some classic books on astronomy. You may like to read them."
The boy spent much time devouring the books in the following months. He then decided to take astronomy as his career and eventually became one of the most outstanding mathematicians and astronomers in the world. His name was Zu Chongzhi.
The Zu family moved to today's Nanjing, capital of Jiangsu Province in eastern China, from the north to escape wars and political turmoil. Both Zu's grandfather and father served in the imperial court of Liu Song Dynasty (AD 420-479). His grandfather was an engineer in charge of construction and his father a technical consultant.
Under the emperor's patronage, the young Zu was sent to study at the Imperial Nanjing University and then the Imperial Institute. Later, he was assigned to work in an office in today's Zhenjiang in Jiangsu Province for the local governor.
During his study and research at those institutes, Zu first concentrated on calculating the value of pi. Thanks to his computation technique which was way ahead of its time, Zu was able to work out the numerical value of pi to be between 3.1415926 and 3.1415927. Zu obtained this extraordinary fraction more than 1,000 years before European scientists. And Zu's pi was later named by other scientists the Zu Chongzhi Fraction.
In AD 465, Zu created a new calendar, the Daming Calendar, for the imperial court. The new calendar was a great improvement over previous calendars and contained many discoveries that Zu had made in astronomy. For instance, Zu calculated the yearly difference based on the movement of the earth's axis in relation to the fixed stars. In other words, he measured the difference between the Sidereal Year and the Tropical Year.
Zu's measurement of 45 years 11 months per degree was rough compared with the difference of 70.7 years per degree as we know today. However, he was the first astronomer in the world to incorporate the measurement into a calendar.
In addition to his contributions to mathematics and astronomy, Zu also made great achievements as an engineer. One of his most outstanding feats is his reinvention of the South Pointing Chariot in AD 478.
Unlike a compass, which relies on magnetism to achieve the north-pointing effect, the South Pointing Chariot was based on complicated gear works to enable a fixed figurine on a chariot to constantly point south. The device was invented by a Chinese mechanical engineer called Ma Jun in AD 255, but later lost in history.
However, both Zu's recreation of the chariot and a comprehensive mathematical book entitled "The Method of Interpolation," which was co-authored by Zu and his son Zu Gengzhi, also a famous mathematician, failed to survive to the present day.
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