An instrument in which a pair of images can be viewed in rapid succession to detect any differences between them; also known as a blink microscope. The images are usually of the same part of the sky, taken at different times. Any object which has moved or changed brightness will appear to jump or blink as the operator switches between the two images. Blink comparators are used to search for asteroids, variable stars, and novae. Images taken using CCD cameras are compared using software which displays them alternately on a computer monitor.