Blink comparison of two photographic plates showing the movement of the dwarf planet Pluto. The photographs were taken on 2nd and 5th March 1930. The photographs are shown alternating one after the other, making the movement of Pluto evident. Pluto was discovered by Clyde Tombaugh in February 1930, in a pair of photographs taken on 23rd and 29th January 1930. Tombaugh used a blink comparator, a machine that rapidly alternated views of two photographs of the same area of sky taken several days apart, like this. Pluto was deemed a planet at the time of its discovery. The discovery of numerous similar-sized bodies orbiting beyond Neptune, led to it being reclassified as a dwarf planet in August 2006. Pluto was visited by the New Horizons spacecraft on 14th July 2015.
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