Zu Geng or Zu Gengzhi (Chinese: 祖暅之; Wade–Giles: Tsu Keng-chih; ca. 480 – ca. 525) was a Chinese mathematician, politician, and writer. His courtesy name was Jingshuo (景爍). He was the son of the famous mathematician Zu Chongzhi.^[1] He is known principally for deriving and proving the formula for the volume of a sphere. He additionally measured the angular distance between Polaris and the celestial north pole, which was greater 1600 years ago than it is today.