190-120 B.C.

Greek astronomer sometimes credited as the father of trigonometry. Hipparchus discovered the precession of the equinoxes, or the shift in direction of Earth's axis of rotation, and produced a calculation of the year's length to within 6.5 minutes of the actual figure. Though his role as father of trigonometry is subject to some dispute, it appears that he laid the foundations for the discipline with his table of chords for solving triangles. He was also the first Greek mathematician to divide the circle into 360 degrees.