A blink comparator is a viewing apparatus formerly used by

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

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, Kingdom of Prussia – 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 C ...

Carl Zeiss AG 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 foundation for today's ...

, then constituted as Carl-Zeiss-Stiftung. Animation

In photographs taken a few days apart, rapidly moving objects such as

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s and

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

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 Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

, or

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

s, or to distinguish

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

s from optical doubles. The most notable object in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

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 Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

, discovered by

Clyde Tombaugh Clyde William Tombaugh (; February 4, 1906 – January 17, 1997) was an American astronomer best known for discovering Pluto, the first object to be identified in what would later be recognized as the Kuiper belt, in 1930. Raised on farms in ...

in 1930. The Projection Blink Comparator (PROBLICOM), invented by amateur astronomer Ben Mayer, is a low-cost version of the professional tool. It consists of two

slide projector A slide projector is an optical device for projecting enlarged images of photographic slides onto a screen. Many projectors have mechanical arrangements to show a series of slides loaded into a special tray sequentially. 35 mm slide p ...

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

amateur astronomers An amateur () is generally considered a person who pursues an avocation independent from their source of income. Amateurs and their pursuits are also described as popular, informal, self-taught, user-generated, DIY, and hobbyist. History ...

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 plate Photographic plates preceded film as the primary medium for capturing images in photography. These plates, made of metal or glass and coated with a light-sensitive emulsion, were integral to early photographic processes such as heliography, d ...

s, 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. The blinking technique is less used today, because image differencing algorithms detect moving objects more effectively than

human eyes The human eye is a sensory organ in the visual system that reacts to visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and keeping balance. The eye can be considered as a living optical device. It is ...

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.http://www.astrometrica.at/ 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