February 18th, 1930 – The Discovery of Pluto

Today-In-History

While studying photographs taken in January, Clyde Tombaugh discovers Pluto on February 18th, 1930.

Clyde-Tombaugh-APS

While a young researcher working for the Lowell Observatory in Flagstaff, Arizona, Tombaugh was given the job to perform a systematic search for a trans-Neptunian planet (also called Planet X), which had been predicted by Percival Lowell and William Pickering.

Clyde_W._Tombaugh

Clyde William Tombaugh (February 4th, 1906 – January 17th, 1997)

Tombaugh used the observatory’s 13-inch astrograph to take photographs of the same section of sky several nights apart. He then used a blink comparator to compare the different images. When he shifted between the two images, a moving object, such as a planet, would appear to jump from one position to another, while the more distant objects such as stars would appear stationary. Tombaugh noticed such a moving object in his search, near the place predicted by Lowell, and subsequent observations showed it to have an orbit beyond that of Neptune. This ruled out classification as an asteroid, and they decided this was the ninth planet that Lowell had predicted. The discovery was made on Tuesday, February 18th, 1930, using images taken the previous month. The name “Pluto” was suggested by Venetia Burney, then an 11-year-old English schoolgirl, who died in April 2009, having lived to see the reclassification of Pluto as a dwarf planet. It won out over numerous other suggestions because it was the name of the Roman god of the underworld, who was able to render himself invisible, and because Percival Lowell‘s initials PL formed the first 2 letters. The name Pluto was officially adopted on May 1st, 1930.

Following the discovery, starting in the 1990s, of other Kuiper belt objects, Pluto began to be seen not as a planet orbiting alone at 40 AU, but as the largest of a group of icy bodies in that region of space. After it was shown that at least one such body was more massive than Pluto, on August 24th, 2006 the International Astronomical Union (IAU) reclassified Pluto, grouping it with two similarly sized “dwarf planets” rather than with the eight “classical planets“.

Simulation showing outer planets and Kuiper belt: a) before Jupiter/Saturn 2:1 resonance, b) scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune, c) after ejection of Kuiper belt bodies by Jupiter

Simulation showing outer planets and Kuiper belt: a) before Jupiter/Saturn 2:1 resonance, b) scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune, c) after ejection of Kuiper belt bodies by Jupiter

Tombaugh’s widow Patricia stated after the IAU’s decision that while Clyde may have been disappointed with the change, since he had resisted attempts to remove Pluto’s planetary status in his lifetime, he would have accepted the decision now if he were alive. She noted that he “was a scientist. He would understand they had a real problem when they start finding several of these things flying around the place.” Hal Levison offered this perspective on Tombaugh’s place in history: “Clyde Tombaugh discovered the Kuiper Belt. That’s a helluva lot more interesting than the ninth planet.”

“Today in History” on The Pandora Society dot com is primarily focused on Victorian and Edwardian history and does not always have a direct connection to Steampunk, Dieselpunk, or whatever punk; in fact it rarely does, but it is our hope that in sharing these historical events they might serve as some inspiration to the writers in our community to create potential alternative history stories which we look forward to reading 🙂


 

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