Blink comparator

[1] 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 distant stars remained stationary.

The Projection Blink Comparator (PROBLICOM), invented by amateur astronomer Ben Mayer, is a low-cost version of the professional tool.

[2] In modern times, charge-coupled devices (CCDs) have largely replaced photographic plates, as astronomical images are stored digitally on computers.

[3][4] The blinking technique is less used today, because image differencing algorithms detect moving objects more effectively than human eyes can.

To measure the precise position of a known object whose direction and rate of motion are known, a "track and stack" software technique is used.