Major Discoveries in a Flip Book

(Dwarf) Planet Pluto Discovered with Blink Comparator from ZEISS

Photo: Classic ZEISS Blink Comparator (Source: ZEISS)

When physicist Carl Pulfrich developed his blink comparator at ZEISS in 1904, he had no idea of just how many important discoveries would be made with his invention.

The instrument makes it possible to switch quickly between two photographs. This is comparable to a flip book – but with only two pictures. If the two images show the same section of the sky at different times, for example, it is easier to distinguish differences between the photographs. In particular, this makes movements and brightness fluctuations visible.

In 1912, using the technology developed at ZEISS, Henrietta Swan Leavitt discovered the relation between the changes in the brightness of certain stars and their luminosity. The slower the brightness of a star changes, the more radiation it emits. However, not all of this radiation actually reaches the Earth. If the total calculable radiation is compared to that measured on the Earth, the difference can be used to determine the distance of the earth from that star. Edwin Hubble later used this method to calculate the distance to our neighboring galaxy Andromeda for the very first time.

Probably the most famous discovery with a ZEISS blink comparator was made in 1930: the young research assistant Clyde Tombaugh discovered the then ninth planet Pluto at the Lowell Observatory in Arizona (USA). He achieved this by comparing two photos that he had taken on 23 and 29 January. He saw that one of the supposed stars was moving in relation to the others. This is typical of planets.

Due to the increasing use of digital camera technology, the blink comparator has now largely lost its significance. Nowadays, it is almost exclusively used for archive research or as a museum piece.

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