How do CCDs (charge coupled devices) work?
CCDs are at the heart of each telephone camera, digital camera and “HandyCam” TV camera . Special purpose CCDs are used for Kepler. When light strikes a piece of silicon, it releases electrons that are free to move about the silicon material. These electrons form a charge or a current, which is measured to determine the amount of light that has fallen on to the silicon. In a CCD, the silicon region is divided electrically into small individual picture elements or pixels with about four hundred elements per cm in each direction, like a very finely divided sheet of graph paper. The free electrons are kept from moving around by permanent channel stops (the vertical lines in the figure) and externally applied voltages (the horizontal lines in the figure). Each pixel can then be thought of as an individual bucket or well that collects electrons. As shown in the animation, first the CCD is exposed to light from a telescope or camera lens. Overtime this produces an image made up of electrons
