How was Pluto discovered?

Answer 1

Pluto was not found by accident. Scientists saw that Neptune did not always move in orbit as it should. Something was pulling it. So, scientists searched for a ninth planet for decades.

Clyde Tombaugh found Pluto in 1930 after nearly a year of examining photographs with a blink comparator which rapidly shifts between two images alowing the observer to see differences in the (astronomical) images as blinking dots.

Answer 2

Pluto was discovered by comparing photographs taken at Lowell Observatory in 1930 by Clyde Tombaugh.

The apparatus used is called a "blink comparator" and works by rapidly shifting back and forth between two images. This assists the observer in identifying differences in the images and thus objects that are the same in both images will appear stationary, any differences will blink, any planet would show up as a blinking dot as it moved across the sky.

In the 1840s it was discovered that 'wobbles' called perturbations in the orbit of Uranus meant that beyond Uranus there was another planet whose gravitational pull caused these perturbations. This led to the discovery of Neptune. However it was realised that the perturbations in Uranus' orbit could not be all due to Neptune and so the search began for another planet even further out. Clyde Tombaugh was given the job of photographing areas of the sky several days or weeks apart and comparing the pictures with the 'blink comparator' . On February 18th 1930, after a year of searching, he finally found Pluto. However, unbeknown to him Pluto had already appeared on charts as long ago as 1915, but had not been identified as a planet.

The strange fact was, though, that on re-examining the Neptune data many years later, an error in data meant that there was no actual discrepancy in the wobble of Neptune - in other words there was no large planet further out responsible for any supposed perturbations. So the discovery of Pluto was, indeed, fortunate.