GEOMETRY: Mathematics Animation: CONICS: movie of conic section: parabola
An parabola is a geometric figure (shown in bright pink) formed when a plane (red) intersects a cone (green) and that plane lies parallel to the edge of that cone. Because the plane lies parallel to the side of the cone it always passes through the base of the cone (shown in bright blue) and so the figure remains open ended unlike an ellipse, which is a related closed figure. Parabolas are very important figures since they describe the trajectory (flight path) of an object that is thrown and is pulled by gravity. Such an object is called "ballistic". Parabolic reflectors are concave mirrors with a parabolic profile (cross-section) that focus incoming rays to a point (focus). These are very important in astronomy where they are used in reflecting telescopes.