1. A means of converting the electromagnetic energy of photons of a particular wavelength into a digital video signal which can be displayed on a television screen.
2. A device for forming images electronically, using a layer of silicon that releases electrons when struck by incoming light.

The electrons are stored in pixels and read off into a computer at the end of the exposure. CCD's have now almost entirely replaced photographic film for applications: such as, astrophotography where extreme sensitivity to light is so important.

Since the mid-1970's, a new type of detector called the charge-coupled device has gained popularity in astronomy.

The CCD is an electronic detector that replaces photographic plates or film.

It converts light into a electric charge, which is used to form images on a computer screen.

The charge-coupled device was developed as a replacement for television camera tubes and is commonly used in today's camcorders.

Modern astronomical CCD's are much larger, with as many as 16 million separate detectors, or pixels.

Because they are far more sensitive to light, charge-coupled devices produce better pictures than traditional photographic methods and astronomers can see extremely faint galaxies in almost any part of the sky.