Using a 13-inch (33-cm) telescope at the Lowell Observatory in Flagstaff, Arizona, Clyde W. Tombaugh, a 24-year-old American with no formal training in astronomy, discovered the dwarf planet Pluto #OTD in 1930.
The music of the spheres : A nature lover's astronomy by Grondal discusses Pluto as well as many other planets:
https://www.gutenberg.org/ebooks/70382
More about Pluto at PG:
https://www.gutenberg.org/ebooks/search/?query=Pluto&submit_search=Go%21