A blink comparator is a viewing apparatus formerly used by

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

s to find differences between two photographs of the night sky. It permits rapid switching from viewing one photograph to viewing the other, "blinking" back and forth between the two images taken of the same area of the sky at different times. This allows the user to more easily spot objects in the night sky that have changed position or brightness. It was also sometimes known as a blink microscope. It was invented in 1904 by physicist

Carl Pulfrich Carl P. Pulfrich (September 24, 1858 in Burscheid, Rhine Province – August 12, 1927 in Baltic Sea, drowned when his canoe capsized) was a German physicist, noted for advancements in optics made as a researcher for the Carl Zeiss company in ...

Carl Zeiss AG Carl Zeiss AG (), branded as ZEISS, is a German manufacturer of optical systems and optoelectronics, founded in Jena, Germany in 1846 by optician Carl Zeiss. Together with Ernst Abbe (joined 1866) and Otto Schott (joined 1884) he laid the f ...

, then constituted as Carl-Zeiss-Stiftung. In photographs taken a few days apart, rapidly moving objects such as asteroids and

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

s would stand out, because they would appear to be jumping back and forth between two positions, while all the distant stars remained stationary. Photographs taken at longer intervals could be used to detect stars with large proper motion, or

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

s, or to distinguish binary stars from optical doubles. The most notable object to be found using this technique is

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...

, discovered by

Clyde Tombaugh Clyde William Tombaugh (February 4, 1906 January 17, 1997) was an American astronomer. He discovered Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper belt. At the time of discovery, Pluto was cons ...

in 1930. The Projection Blink Comparator (PROBLICOM), invented by amateur astronomer

Ben Mayer Ben Mayer (1925 in Germany – 28 December 1999) was an amateur astronomer perhaps best known for the invention of the projection blink comparator (PROBLICOM), a low-cost version of the blink comparator. This inexpensive tool allowed amateur astr ...

, is a low-cost version of the professional tool. It consists of two

slide projector A slide projector is an opto-mechanical device for showing photographic slides. 35 mm slide projectors, direct descendants of the larger-format magic lantern, first came into widespread use during the 1950s as a form of occasional hom ...

s with a rotating occluding disk that alternately blocks the images from the projectors. This tool allowed

amateur astronomers Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomer ...

to contribute to some phases of serious research.

Modern replacements

In modern times,

charge-coupled device A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

s (CCDs) have largely replaced photographic plates, as astronomical images are stored digitally on computers. The blinking technique can easily be performed on a computer screen rather than with a physical blink comparator apparatus as before.Blink Comparator on PC http://www.instructables.com/id/Blink_Comparator_on_Personal_Computer The blinking technique is less used today, because

image differencing Image differencing is an image processing technique used to determine changes between images. The difference between two images is calculated by finding the difference between each pixel in each image, and generating an image based on the result. Fo ...

algorithms detect moving objects more effectively than

human eyes The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. Th ...

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. Multiple images are superimposed such 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.

References

{{DEFAULTSORT:Blink Comparator Astronomical imaging Optical devices Observational astronomy Products introduced in 1904 1904 in science Carl Zeiss AG

Modern replacements

See also

References