Blink comparator

Blink comparator

A blink comparator was a viewing apparatus used by astronomers to find differences between two photographs of the night sky shot using optical telescopes such as astrographs. It permitted rapidly switching from viewing one photograph to viewing the other, "blinking" back and forth between the two taken of the same area of the sky at different times. This allowed the user to more easily spot objects in the night sky that changed position. It was also sometimes known as a blink microscope.


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.

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.

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. [Blink Comparator on PC] 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.

Modern replacements

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.

See also

* Hinman Collator
* vdiff


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Look at other dictionaries:

  • Blink comparator — Comparateur à clignotement Comparateur à clignotement de l Observatoire Lowell utilisé lors de la découverte de Pluton. Un comparateur à clignotement est un dispositif opto mécanique autrefois utilisé par les astronomes pour faire apparaître les… …   Wikipédia en Français

  • blink comparator — an optical instrument used to detect small differences in two photographs of the same field or object by viewing them alternately, switching rapidly from one to the other. [1925 30] * * * …   Universalium

  • blink comparator — noun : an optical instrument by means of which two pictures identical in all but a few details may be registered in a single visual field and viewed alternately in rapid succession * * * an optical instrument used to detect small differences in… …   Useful english dictionary

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  • blink microscope — noun : a blink comparator in which the compared images are magnified * * * blink microscope, an instrument through which two photographs may be viewed in rapid alternation to check the alteration in position or movement of a star, comet, or other …   Useful english dictionary

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