How was the dwarf planet Pluto discovered?
A) by prediction using Newton's laws to account for the deviations from uniform orbits of Uranus and Neptune
B) by the infrared cameras on the IRAS spacecraft
C) by Voyager spacecraft cameras, which were used between planetary encounters to survey the planetary system
D) by searching photographs of the sky for an object that moved against the background of distant stars

Question

Quizplus · Accepted Answer

Pluto was discovered by Clyde Tombaugh in 1930 through a meticulous examination of photographic plates. He was searching for a predicted Planet X by comparing images of the night sky taken weeks apart, looking for objects that moved against the backdrop of fixed stars, indicating a planet within our solar system.

How Was the Dwarf Planet Pluto Discovered