| Zu Chongzhi (430-501)
Also known as Tsu Ch'ung Chi, Tsu Ch'un-Chi, Zu Chong-zhi, Zu Chong Ji, or Zu Chong-Ji
Zu was born in Fan-yang, modern day Hebei (also referred to as Hopeh province, China. He was a brilliant mathematician, engineer, and astronomer of his time. Unfortunately, he is one of the least credited scientists. Because most of the records about him were lost, it is very hard to find any information about his life or his works. This is an essay about his achievements and his genius.
Zu gave an approximation of 355/113 to pi, which was six decimal places correct. This number was used by mankind for over 900 years after his death. He also made a remarkable proof that 3.1415926 < pi < 3.1415927. Unfortunately, the people of today cannot know exactly how he did it because the book that he wrote with his son that described the proof in detail was lost. Zu, along with his father, also derived the formula for the volume of a sphere.
His astronomical achievements included the making of a new calendar, which was never used. He also determined the exact time of the solstice. He did that by measuring the length of the Sun's shadow at noon on days near the solstice. By doing that, he reduced the errors caused by the fact that it is very difficult to determine the exact time of the solstice.
Zu Chongzhi was a great scientist of his time. His great achievements in mathematics and astronomy led modern astronomers to name a crater of the moon after him.
PS. I tried to find out how Zu Chongzhi's calendar worked, but nobody seems to know. There are also a lot of texts in Chinese, but I can't read them.
http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Tsu.html
http://faculty.oxy.edu/jquinn/home/Math490/Timeline/430AD.html
Thanks to Excalibre and JerboaKolinowski for finding all the different names. | 
