On the 15 March 1980 episode of The Sky at Night, Patrick Moore spoke to one of the heroes of his youth, Clyde Tombaugh, who had discovered Pluto 50 years previously in 1930.
An amateur astronomer with no degree, Tombaugh was nonetheless given a job at the Lowell Observatory after sending them drawings he’d made of Mars and Jupiter. Their detail so impressed the observatory staff that he was given the role of operating their new 13-inch refractor. Now known as the Pluto Telescope, it was specifically designed to look for signs of a new planet at the edge of the Solar System.
Night after night, Tombaugh took deep images of the night sky. The exposures needed to be over an hour long to stand a chance of detecting such distant objects, and with no modern tracking he had to constantly check the guide scope to ensure the telescope stayed on target.
Once the images were developed, he would compare plates taken on sequential nights, looking for signs of a planet moving against the fixed background stars. On 18 February 1930, he finally saw it.
“It was one of the best suspects I’d run into in many months,” said Tombaugh. “I looked in there and spied it almost immediately. A tremendous thrill came over me. I almost shook.”
We now know that Pluto is just one of many large object in the region beyond Neptune known as the Kuip
