The search for Pluto was not a moment of sudden, “Eureka!” inspiration, but rather a grueling marathon of mental endurance. When Clyde Tombaugh arrived at the Lowell Observatory in 1929, he was assigned a task that had already defeated several senior astronomers: finding “Planet X.” This theoretical ninth planet was predicted by the observatory’s founder, Percival Lowell, who believed an unseen mass was tugging on the orbits of Uranus and Neptune.
To find it, Clyde used a machine called a Blink Comparator. The process was incredibly tedious:
- He would take two photographs of the same patch of sky, spaced several days apart.
- Each plate contained hundreds of thousands of stars.
- The Blink Comparator would rapidly alternate (or “blink”) between the two images.
- Since stars are too distant to appear to move, they stayed still. However, a planet—being much closer—would appear to “jump” back and forth between the two frames.
For nearly a year, Clyde sat in a dark room for hours every day, peering through an eyepiece at over two million individual stars. Finally, on the afternoon of February 18, 1930, while examining plates taken the previous month, he noticed a tiny, 15th-magnitude speck flickering in the constellation Gemini. After months of painstaking silence, he walked into the director’s office and calmly stated, “Dr. Slipher, I have found your Planet X.”
Why Pluto?
Once the discovery was announced on March 13, 1930 (the anniversary of Lowell’s birth and the discovery of Uranus), the observatory was flooded with over 1,000 suggestions from around the world. Names like Cronus, Minerva, and even “Percival” were tossed around, but the winning name came from an unlikely source: an 11-year-old schoolgirl in Oxford, England, named Venetia Burney.
Venetia, who was interested in classical mythology, suggested Pluto—the Roman god of the underworld who was able to render himself invisible. She felt the name was fitting for a planet that lived in the dark, lonely outer reaches of the solar system. Her grandfather, a librarian at Oxford University, passed the suggestion to a professor, who cabled it to the Lowell Observatory.
The staff at Lowell loved the name for three specific reasons:
- Mythological Consistency: It followed the tradition of naming planets after Roman deities.
- The Underworld Connection: It honored the dark, cold nature of a world so far from the sun.
- A Hidden Tribute: The first two letters, P and L, formed a monogram for Percival Lowell, the man who had dedicated his life and fortune to the search.
On May 1, 1930, the name was formally adopted, and Venetia Burney was awarded £5 (roughly $300 today) as a prize for her contribution to astronomical history.
Clyde Tombaugh 