Comparison of two photographic plates showing the movement of the dwarf planet Pluto, on 2nd March 1930 and on 5th March 1930. The photographs are first shown one after the other, and then shown annotated with arrows to highlight Pluto. 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, which presented two photographs of the same area of sky taken several days apart. By flicking rapidly between the two, any moving object is evident amongst the fixed stars. 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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