This blink comparator at Lowell Observatory was used in the discovery of Pluto.

A blink comparator was a viewing apparatus used by astronomers to find differences between photographic plates taken of the same area of the sky at different times. It was also sometimes known as a blink microscope. Image File history File links Download high resolution version (1941x2226, 400 KB)Blink comparator at Lowell Observatory used in the discovery of Pluto. ... Image File history File links Download high resolution version (1941x2226, 400 KB)Blink comparator at Lowell Observatory used in the discovery of Pluto. ... Lowell Observatory Percival observing Mars from the Clark telescope at the Lowell Observatory. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Photography is the process of making pictures by means of the action of light. ...

It permitted rapidly switching from viewing one plate to viewing the other, "blinking" back and forth between the two views. In plates 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. Plates 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. An asteroid is a predominantly rocky body that orbits around its star. ... Comet Hale-Bopp For other uses, see Comet (disambiguation). ... The proper motion of a star is the motion of the position of the star in the sky (the change in direction in which we see it, as opposed to the radial velocity) after eliminating the improper motions of the stars, which affect their measured coordinates but are not real... Most stars are of almost constant luminosity. ... Artists impression of a binary star system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... This topic is about the astronomical phenomenon. ...

The most notable body to be found using this technique was Pluto, discovered by Clyde Tombaugh in 1930. Atmospheric characteristics Atmospheric pressure 0. ... An image of Clyde Tombaugh Clyde William Tombaugh (February 4, 1906 – January 17, 1997) was an American astronomer who discovered the dwarf planet Pluto in 1930. ... 1930 (MCMXXX) is a common year starting on Wednesday. ...

The Projection Blink Comparator (PROBLICOM), invented by amateur astronomer Ben Mayer, was a low-cost version of the professional tool. It consisted of two slide projectors with a rotating occulting disk that alternately blocked the images from the projectors. This tool allowed amateur astronomers to contribute to some phases of serious research. Ben Mayer (? - 2000) was an amateur astronomer perhaps best known for the invention of the Projection Blink Comparator (PROBLICOM). ... It has been suggested that this article or section be merged with Skygazing. ...

In modern times, CCDs have largely replaced photographic plates and astronomical images are stored digitally on computer. The blinking technique can easily be performed on a computer screen rather than with a physical blink comparator apparatus as before. For example, a recently proposed method allows a radiologist to compare new and old digital medical images (MRI, CT, xrays, etc.) with greater accuracy and efficiency using a digital blink comparator method. A specially developed CCD used for ultraviolet imaging in a wire bonded package. ...

However, the blinking technique is less used than before because image differencing algorithms are often used to detect moving objects more effectively than human eyes are capable of. Or, to measure the precise position of a known object whose direction and rate of motion are known, a "track and stack" technique is used in which multiple images are superimposed by software in such a way that the moving object is fixed in place; the moving object then stands out as a dot among the star trails. This is particularly effective in cases where the moving object is very faint and superimposing multiple images of it permits it to be seen better. Image differencing is an image processing technique used to determine changes between images. ...

See also

• Hinman Collator