An electronic light detector that converts photons into electrical signals by storing charge in an array of pixels, then transferring this charge sequentially to create a digital image. CCDs revolutionized astronomy by being far more sensitive than photographic film and providing linear response to light intensity.
Named for its mechanism of transferring electrical charge between coupled capacitors, from 'charge' (Old French 'charger'), 'coupled' (Latin 'copula' for bond), and 'device' (Old French 'devis'). Invented at Bell Labs in 1969 for telecommunications, CCDs were quickly adopted by astronomers in the 1970s who recognized their revolutionary potential for detecting faint celestial objects.
CCDs are so sensitive they can detect individual photons that traveled billions of years across the universe - they're literally counting particles of ancient light one by one! A single CCD pixel can detect light 100 times fainter than photographic film, which is why the switch from film to CCDs in the 1980s suddenly revealed galaxies and stars that had been invisible to all previous generations of astronomers.
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