Themes > Science > Astronomy > Equipment and Devices > Recording Images

Throughout most of the history of astronomy scientists have viewed celestial objects through a telescope's eyepiece. When photography was invented in the 1800s, one of its first applications was to attach a camera to a telescope to make a photograph of the moon. Photography permitted astronomers to record and archive what they saw. Photographic time exposures exceeded the eye's sensitivity and recorded very faint objects, often in rich colors. Today, photographic film in telescopes has been largely replaced by solid-state detectors, called charge-coupled devices (CCDs). These thumbnail-sized silicon chips are divided into millions of picture elements, called pixels, that convert incoming starlight into an electrical charge that is read by computer. The resulting mosaic of bright and dark pixels creates a picture. CCDs provide much greater sensitivity and contrast than photographs do, and the image is automatically recorded in digital form for subsequent storage and enhancement by computer image processing. CCDs can also record more wavelengths of light than cameras can, from the visual edge of the ultraviolet region to the near-infrared.