Mathematician:Oenopides of Chios

Mathematician, geometer and astronomer.

Little is known about him except that he came from the island of Chios, and is generally believed to have lived and worked in Athens in his youth.

Estimated the tilt of the Earth's axis with respect to the ecliptic as $24^\circ$.

Appears to have introduced the rule that all geometric constructions must be done with a straightedge and compass.

Nationality
Greek

History

 * Born: c. 490 BCE, Chios (now Khios), Greece
 * Died: c. 420 BCE

Theorems and Definitions

 * Perpendicular through a Given Point, documented as Proposition 12 of Book I in by Euclid.
 * Construction of an Equal Angle, documented as Proposition 23 of Book I in by Euclid.