Applications of Concave Mirrors

Satellite Dish diagramOne very important application of concave mirrors is in the familiar "satellite dish". These antennas are designed to receive and amplify weak signals sent from communications satellites in space. Since these satellites are so far away, the waves that reach the earth from them are practically parallel. When these waves strike a properly-aimed concave mirror, they are all reflected through the focus of the mirror. At the focus is placed the receiver for the signals. The purpose of the mirror is to gather the weak signals over a large area and concentrate them in one spot.

Another example of the practical application of concave mirrors is the headlights of your car. A small but powerful light source is placed at the focus of the concave mirror that forms the back of the headlight. Any light from the focus that strikes the mirror will be reflected parallel to the axis of the mirror. This is how the headlight beam is formed.

Another important application of concave mirrors is the astronomical telescope. All large telescopes (and many small ones) use a large concave mirror at the bottom of the telescope to gather light and form a small image on a small plane mirror at the top. The purpose of the plane mirror is simply to reflect the light into the eyepiece (or camera or other instrument) of the telescope. Larger mirrors gather more light, enabling astronomers to see fainter objects. Many people not familiar with astronomy think that the enlarging power of a telescope is the most important, but this is only true when you are observing relatively nearby objects, like the moon or a planet. Stars are so far away that they appear to be points of light - no matter how much they are enlarged. A large astronomical telescope does not enlarge the image as much as it enables one to see a fainter image.

last update September 20, 1999 by JL Stanbrough