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Two photos from Lowell Observatory showing a fields of white stars on a black background. A pair of arrows in each photo shows a small dot that has changed position – Pluto. The caption underneath reads HOW PLUTO WAS FOUND WHITE DOT MOVES AMONG THE STARS The ninth and most distant planet was discovered by comparing these two photographs of the same section of the sky taken six nights apart, on January 23, 1930 (right) and January 29 (left). Arrows point to the dot that represents Pluto. The movement indicates that the object was relatively nearer the Earth, and therefore must be a planet. The other white dots are stars, and show no movement between pictures because they are so far away (page 16).