Parabolic reflector

A reflecting surface shaped as a paraboloid that sends parallel rays to a focus or reflects rays from that focus into a parallel beam.

Paraboloid: A three-dimensional surface formed by rotating a parabola around its axis of symmetry. The reflector’s surface is a paraboloid, giving every axial ray the same optical path to the focus.
Reflecting telescope: A telescope that uses a mirror to collect and focus light. Its primary mirror is commonly parabolic to bring distant, nearly parallel light to a focus.
Spherical mirror: A mirror whose reflecting surface is part of a sphere. Unlike a paraboloid, it does not focus parallel axial rays to one exact point.
Electromagnetic radiation: Energy that propagates through space as coupled oscillating electric and magnetic fields. Visible light and radio waves can both be focused by suitably shaped reflectors.
Herschelian telescope: A reflecting telescope design that places its eyepiece near the front edge of the tube. William Herschel used a tilted parabolic primary mirror to keep the observer out of the incoming beam.
Parabola: A plane curve whose points are equally distant from a fixed point and a fixed line. A paraboloid is generated by rotating this curve around its axis.
Radio telescope: An instrument that detects radio waves from astronomical sources using an antenna. Its dish often uses a parabolic surface to concentrate incoming radio waves at a receiver.
Ellipsoidal reflector: A reflector shaped as part of an ellipsoid, with two distinct focal points. It transfers rays between two foci rather than mapping parallel rays to one focus.
Plane wave: A wave whose surfaces of constant phase are parallel planes. At large distances, incoming radiation is often approximated as a plane wave with parallel rays.
Arecibo Observatory: A former radio observatory in Puerto Rico, known for its enormous fixed dish antenna. Its spherical primary reflector required corrective optics to handle the resulting aberrations.

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