Parabola

Parabola, geometrical curve, similar in shape to the path followed by a projectile when it is fired into the air. A parabola is a conic section, obtained by the intersection of a right circular cone and a plane. If a parabola is rotated about its axis, it traces out a three-dimensional parabolic surface. When a light source is placed at the focus of a mirror with this shape, all the light rays are reflected parallel to the axis. A reflecting telescope uses the principle in reverse, collecting parallel rays of light from space and concentrating them at the focus.