Clyde Tombaugh

Clyde William Tombaugh was born on February 4, 1906, on a farm near Streator, Illinois, the eldest of six children of Muron and Adella Tombaugh ^[1]. His father farmed rented land, and money was always short. An uncle owned a small telescope, and through it the young Tombaugh got his first serious look at the Moon and planets, an experience that fixed his ambitions early. When he was in his teens the family moved west to a farm near Burdett, Kansas, hoping for better prospects ^[2].

Kansas dealt the family a hard blow. A hailstorm destroyed the crops that were meant to pay for Clyde's college education, and the plan for formal study had to be abandoned ^[1]. He graduated from Burdett High School in 1925 and stayed on the farm, but he refused to give up astronomy. Working from books and magazine articles, he taught himself optics and began grinding telescope mirrors by hand. His materials were whatever the farm could supply: parts of a cream separator, a shaft from his father's 1910 Buick, and a cellar he dug himself to provide the stable temperatures that fine optical work requires ^[2].

By 1928 he had completed a 9-inch reflecting telescope of genuine quality. With it he made careful drawings of Jupiter and Mars at the eyepiece, night after night, recording detail with the discipline of a trained observer. Wanting a professional opinion of his work, he mailed the drawings to Lowell Observatory in Flagstaff, Arizona ^[3]. It was a long shot from a farm kid with no credentials, and it changed his life.

The drawings arrived at Lowell Observatory at a fortunate moment. The observatory's director, Vesto Melvin Slipher, was preparing to restart the search for a trans-Neptunian planet that the observatory's founder, Percival Lowell, had pursued until his death in 1916. Lowell had called the hypothetical body Planet X and had predicted its position from what he believed were irregularities in the orbit of Uranus ^[4]. Slipher needed a careful, tireless observer who could be hired cheaply, and Tombaugh's drawings suggested exactly that combination. In January 1929 the 22-year-old left Kansas by train for Flagstaff, hired on a trial basis ^[3].

His assignment was brutal in its monotony. Using a new 13-inch photographic telescope, Tombaugh exposed large glass plates of the sky along the zodiac, each capturing tens of thousands to hundreds of thousands of star images. Plates of the same region taken several nights apart were then loaded into a device called a blink comparator, which flips the view rapidly between the two plates. Stars stay fixed; anything in the solar system shifts position and appears to jump ^[4]. Tombaugh spent his days at the comparator, checking star images one by one, and his nights in an unheated dome making new exposures in the Arizona winter.

Who was Clyde Tombaugh at this point? Officially, a junior assistant without a degree, paid a modest wage and expected to stoke the observatory furnace along with his scientific duties. Unofficially, he was becoming one of the most methodical planet hunters ever to work in the field, examining millions of star images with a rigor the earlier Lowell searches had never matched ^[2].

On the afternoon of February 18, 1930, Tombaugh was blinking plates of a field near the star Delta Geminorum, taken on January 23 and January 29. A faint image, far dimmer than Lowell's predictions had suggested, jumped by the small amount expected for an object beyond Neptune ^[4]. He checked a third plate and an earlier poor-quality pair, and the object was there too, moving consistently. After about 45 minutes of verification he walked into the director's office and announced that he had found Planet X ^[3].

The observatory spent weeks quietly confirming the object's motion before making the news public on March 13, 1930, a date chosen because it was both the anniversary of Percival Lowell's birth and of William Herschel's discovery of Uranus ^[1]. The announcement caused a worldwide sensation. Name suggestions poured in, and the observatory settled on Pluto, the Roman god of the underworld, proposed by Venetia Burney, an 11-year-old schoolgirl in Oxford, England. The name's first two letters also honored Percival Lowell's initials ^[5].

Among the most striking Clyde Tombaugh facts is that the discovery, in a sense, rested on a coincidence. Later measurements showed Pluto was far too small to have produced the orbital irregularities Lowell thought he had detected; those irregularities largely vanished once the mass of Neptune was refined. Pluto happened to lie near the predicted spot, but it was Tombaugh's exhaustive, systematic search that actually found it ^[4]. He did not stop there. He continued blinking plates for years afterward, eventually examining an estimated 90 million star images, and demonstrated that no other comparably bright planet existed in the regions he covered ^[2].

Any honest account of Clyde Tombaugh achievements has to reach well past a single famous afternoon. His plate searches through the 1930s and early 1940s produced a large catalog of incidental discoveries: hundreds of asteroids (more than a dozen of which he was credited with discovering formally), several galactic star clusters, a comet, and evidence for large groupings of galaxies, including a concentration in Perseus and Andromeda that he described as a great supercluster ^[2]. Few observers in history have inspected the sky so thoroughly by eye.

Recognition brought opportunity. The Royal Astronomical Society of Great Britain awarded him its Jackson-Gwilt Medal in 1931 for the Pluto discovery ^[3]. A scholarship for the discoverer enabled him, at last, to attend college: he enrolled at the University of Kansas in 1932, already world famous, and earned a bachelor's degree in astronomy in 1936 and a master's degree in 1939 ^[1]. He returned to Lowell between academic terms to continue the planet search.

During the Second World War Tombaugh taught navigation for the United States Navy at Arizona State Teachers College in Flagstaff. In 1946 he moved to New Mexico to work at the White Sands Proving Ground, where captured German V-2 rockets and early American missiles were being tested. He designed and supervised optical tracking systems, including telescope instrumentation that could follow fast-moving rockets in flight and record their behavior for engineers ^[6]. It was exacting optical work of the kind he had been doing since the cellar in Kansas, now applied to the opening years of the American rocket program.

Tombaugh married Patricia Edson, known as Patsy, in 1934; the two had met through her brother, a fellow astronomy student at the University of Kansas ^[1]. The marriage lasted more than six decades, until his death. The couple raised two children, Annette and Alden, and eventually settled permanently in Las Cruces, New Mexico ^[6].

Those who knew him described a plainspoken, humorous man who never lost the habits of the farm. He was famous among colleagues for his stockpile of puns, delivered with evident delight. He remained a hands-on amateur at heart even as a professional: he kept building telescopes throughout his life, and he never parted with the 9-inch reflector he had made from farm machinery in 1928, which he continued to use for decades ^[2]. He was also active in his community and, with Patsy, a familiar presence in Las Cruces civic life.

He took the public's endless fascination with Pluto in stride. When the National Air and Space Museum sought to acquire his homemade telescope, he reportedly declined for years because he was still observing with it. He answered letters from schoolchildren about the ninth planet well into old age, and he lived long enough to see NASA begin planning the mission that would eventually visit it ^[5].

In 1955 Tombaugh joined the faculty of New Mexico State University in Las Cruces, where he founded the astronomy research program and helped build it into a department that awards graduate degrees ^[6]. He led a planetary photography program, studied the surface of Mars, and conducted a systematic search commissioned by the Army for small natural satellites of Earth. The search found none, a null result that mattered as spaceflight approached, since planners needed to know whether debris hazards existed in near-Earth space ^[2].

He formally retired in 1973 as professor emeritus but kept an office and a steady presence at the university, lecturing widely and raising money for the observatory facilities that now serve the department ^[6]. In 1980, for the fiftieth anniversary of the discovery, he and the writer Patrick Moore published Out of the Darkness: The Planet Pluto, a book-length account of the search and its aftermath ^[7].

Tombaugh died at his home in Las Cruces on January 17, 1997, a few weeks short of his ninety-first birthday ^[1]. His death was reported around the world, with obituaries noting that he had been the only living person to have discovered a planet in the solar system. New Mexico State University later named its campus observatory in his honor.

Pluto's reclassification came after his death. In 2006 the International Astronomical Union defined the term planet in a way that excluded Pluto, designating it a dwarf planet instead, a decision that provoked public argument that has never entirely died down ^[5]. Yet the change arguably enlarged Tombaugh's legacy rather than shrinking it. Pluto proved to be the first known member of the Kuiper Belt, a vast population of icy bodies beyond Neptune, which means Tombaugh had detected the first object of an entirely new region of the solar system decades before anyone knew it existed ^[4].

His discovery received an extraordinary posthumous tribute. When NASA's New Horizons spacecraft launched toward Pluto in January 2006, it carried a small container holding a portion of Tombaugh's ashes, inscribed as a memorial to the discoverer ^[8]. On July 14, 2015, the spacecraft flew past Pluto and returned images of a strikingly varied world. The large, bright, heart-shaped region on its surface was named Tombaugh Regio in his honor, and his children were present at mission control for the encounter ^[8].

For readers of any Clyde Tombaugh biography, the enduring lesson is less about Pluto than about the man's method. He entered professional astronomy with no degree, no money, and no connections, only homemade instruments and an unusual capacity for sustained, careful work. Asteroid 1604 Tombaugh carries his name, as does a crater on Mars ^[3]. He is remembered as proof that in observational science, persistence at the eyepiece and honesty about what one sees can still count for everything.