A parabolic reflector (also known as a parabolic dish or a
parabolic mirror) is a reflective device formed in the shape of a paraboloid
of revolution. Parabolic reflectors can either collect or distribute energy
such as light, sound, or radio waves.
The parabolic reflector functions due to the geometric properties of
the paraboloid shape: if the angle of incidence to the inner surface
of the collector equals the angle of reflection, then any incoming ray
that is parallel to the axis of the dish will be reflected to a central
point, or "focus". Because many types of energy can be reflected
in this way, parabolic reflectors can be used to collect and concentrate
energy entering the relector at a particular angle. Similarly, energy
radiating from the "focus" to the dish can be transmitted
outward in a beam that is parallel to the axis of the dish.
Isaac Newton introduced parabolic mirrors into practical astronomy
when he invented the reflecting telescope. The most common applications
of the parabolic reflector are in satellite dishes, telescopes (including
radio telescopes), parabolic microphones, and many lighting devices
such as spotlights, car headlights, and LED housings.
Parabolic reflectors suffer from an aberration called coma. This is
only of interest in telescopes because other applications don't require
sharp resolution off the axis of the parabola.