A Kansas farm boy spots Pluto in a blink
On this day · 18 February 1930
Comparing photographic plates taken nights apart, Clyde Tombaugh caught a tiny dot shifting against the stars.
On February 18, 1930, a 24-year-old assistant at Lowell Observatory near Flagstaff, Arizona, found a new world. Clyde Tombaugh, a self-taught astronomer from a Kansas farm, had been hired to photograph the same patches of sky several nights apart and hunt for the long-predicted Planet X.
His tool was a blink comparator, which flicked rapidly between two plates of identical star fields. Anything that had moved would appear to jump back and forth while the fixed stars stayed put. Studying plates exposed a few weeks earlier, Tombaugh noticed a faint dot hopping between frames.
The object orbited far beyond Neptune, and the search for a ninth planet was over.
The name Pluto, suggested by an 11-year-old English schoolgirl, was adopted that May. For 76 years it counted as the ninth planet, until 2006, when the discovery of similar Kuiper Belt bodies led astronomers to reclassify it as a dwarf planet.
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