Tsu Ch'ung Chi
Born: 430 in Fan-yang (now Hopeh),
China
Died: 501 in China
Tsu was a Chinese mathematician and astronomer.
He gave the rational approximation 355/113 to p which is correct to 6 decimal places. He also proved that
3.1415926 < p < 3.1415927
a remarkable result on which it would be nice to have more details but Tsu Ch'ung Chi's book, written with his son, is lost.
Tsu's astronomical achievements include the making of a new calendar in 463 which never came into use.
Tsu also determined the precise time of the solstice by measuring the length of the Sun's shadow at noon on days near the solstice to reduce errors caused by the fact that it is very difficult to determine the exact time of the solstice.