An angle is a geometric figure created by two line segments that extend from a single point or two planes which extend from a single line. The size of an angle, measured in units of degrees or radians, is related to the amount of rotation required to superimpose one of its sides on the other. First used by ancient civilizations, angles continue to be an important tool to science and industry today.

The study of angles has been known since the time of the ancient Babylonians (4,000-300 b.c.). These people used angles for measurement in many areas such as construction, commerce, and astronomy. The ancient Greeks developed the idea of an angle further and were even able to use them to calculate the circumference of the Earth and the distance to the moon.

A geometric angle is formed by two lines (rays) that intersect at a common...