Historische Organisatie
Lowell Observatory
Clyde Tombaugh found a moving point in the photographic plates he had been comparing.
By comparing images of the same star field, Tombaugh detected the movement of the object later named Pluto.
The discovery itself took place on 18 February; public announcement and naming came later.
The object initially joined the planetary list and was reclassified as a dwarf planet many decades afterward.
