Working with designers HKD, we created one of these historical astronomical devices for the Hong-Kong Space Museum. A blink comparator was a viewing apparatus used by astronomers to find differences between two photographs of the night sky. It permitted the switching, or ”blinking” back and forth between two photos taken of the same area of the sky at different times. In photographs taken a few days apart, rapidly moving objects such as asteroids and comets would stand out, because they would appear to be jumping back and forth between two positions, while all the other fixed stars stood still. Photographs taken at longer intervals could be used to detect stars with large proper motion, or variable stars, or to distinguish binary stars from optical doubles. The most notable body to be found using this technique was Pluto, discovered by Clyde Tombaugh in 1930.