Tombaugh, Clyde W. (1906-1997)

Tombaugh, Clyde W. (1906-1997)

American astronomer

Clyde W. Tombaugh, an astronomer and master telescope maker, spent much of his career performing a painstaking photographic survey of the heavens from Lowell Observatory in Flagstaff, Arizona. This led to the discovery of Pluto (1930), the ninth planet in the solar system . Although Tombaugh is best known for this early triumph, he went on to make other contributions, including his work on the geography of Mars and studies of the distribution of galaxies. Tombaugh also made valuable refinements to missile-tracking technology during a nine-year stint at the U.S. Army's White Sands Proving Grounds in New Mexico.

Clyde William Tombaugh, the eldest of six children, was born to Muron Tombaugh, a farmer, and Adella Chritton Tombaugh. He spent most of his childhood on a farm near Streator, Illinois. In 1922, the family relocated to a farm in western Kansas. Tombaugh glimpsed his first telescopic view of the heavens through his uncle Leon's 3-in (7.6-cm) refractor, a kind of telescope that uses a lens to gather faint light from stars and planets. In 1925, inspired by an article in Popular Astronomy, Tombaugh bought materials to grind an 8-in (20.3-cm) light-collecting mirror for a reflecting telescope. He ground that first mirror by hand, using a fence post on the farm as a grinding stand.

The finished instrument, a 7-ft (2.1-m) rectangular wooden box, was equipped with wooden setting circles for aligning it to objects of interest in the sky. Tombaugh had not ground the mirror very accurately, and thus the telescope was unsuitable for the planetary observing he had in mind. However, it launched a lifetime of building, improving, and maintaining telescopes, tasks at which Tombaugh excelled. Tombaugh biographer and amateur astronomer David H. Levy estimated that Tombaugh ground some 36 telescope mirrors and lenses in his career. He continued to use a few of his early telescopes for decades after he first constructed them (for example, his 9-in [23-cm] reflector, whose mechanical mounting included parts from a 1910 Buick).

Tombaugh's 9-in reflector, which he completed in 1928, led to a career as a professional observer as well as to sharper views of the planets and stars. After a 1928 hailstorm wiped out the Tombaughs'wheat crop and foiled Clyde's plans for college, the young observer turned his new telescope to Jupiter and Mars. Subsequently, he sent his best drawings of these planets to Lowell Observatory, which had been founded in the late nineteenth century by famed Mars watcher Percival Lowell.

Hoping only for constructive criticism of his drawings, Tombaugh instead received a job offer from the astronomers at Lowell. He accepted, and in January 1929 began his work on the search for the predicted ninth planet beyond the orbit of Neptune. Working full time as a professional observer (although lacking any formal education in astronomy ), Tombaugh used Lowell's 13-in (33-cm) telescope to systematically photograph the sky. He then used a special instrument, called a blink comparator, to examine the plates for telltale signs of moving bodies beyond the orbit of Earth. A blink comparator, or blink microscope, rapidly alternates—up to 10 times per second—two photographic images, taken at different times, of the same field or area of the sky. Seen through a magnifying lens, moving bodies will appear to jump back and forth or "blink" as the images are switched.

Using his knowledge of orbital mechanics and his sharp observer's eye, Tombaugh was able to discern asteroids and comets from possible planets; a third "check" plate was then taken to confirm or rule out the existence of these suspected planets. On February 18, 1930, after 10 months of concentrated, painstaking work, Tombaugh zeroed in on Pluto, fulfilling a search begun by Percival Lowell in 1905. The discovery of Pluto secured the 24-year-old Tombaugh's reputation and his place in the history of astronomy, and he remained with the survey until 1943.

After his discovery, Tombaugh took some time off to obtain his formal education in astronomy. He left for the University of Kansas in the fall of 1932, returning to Lowell each summer to resume his observing duties. At college, he met Patricia Irene Edson, a philosophy major. They married in 1934, and subsequently had two children. Tombaugh paused only once more for formal education in science, taking his master's degree in 1939 at the University of Kansas. For his thesis work, he restored the university's 27-in (68.6-cm) reflecting telescope to full operational status and studied its observing capabilities.

In 1943, Tombaugh taught physics at Arizona State Teachers College in Flagstaff; that same year, the U.S. Navy asked him to teach navigation, also at Arizona State. In what little spare time remained, Tombaugh struggled to continue the planet survey. The following year, he taught astronomy and the history of astronomy at the University of California in Los Angeles. Tombaugh's stint on the planet survey ceased abruptly in 1946. Citing financial constraints, observatory director Vesto M. Slipher asked Tombaugh to seek other employment.

Tombaugh's contribution to the "planetary patrol" at Lowell proved enormous. From 1929 to 1945, he cataloged many thousands of celestial objects, including 29,548 galaxies, 3,969 asteroids (775 of them previously unreported), two previously undiscovered comets, one nova, and, of course, the planet Pluto. However, as Tombaugh pointed out to biographer David Levy, tiny Pluto cast a long and sometimes burdensome shadow over the rest of his career, obscuring subsequent astronomical work. For instance, in 1937, Tombaugh discovered a dense cluster of 1,800 galaxies, which he called the "Great Perseus-Andromeda Stratum of Extra-Galactic Nebula." This suggested to Tombaugh that the distribution of galaxies in the universe may not be as random and irregular as some astronomers believed at the time.

Tombaugh was also an accomplished observer of Mars. He predicted in 1950 that the red planet, being so close to the asteroid belt, would have impact craters like those on the moon . These craters are not easily visible from Earth because Mars always shows its face to astronomers fully or nearly fully lighted, masking the craters' fine lines. Images of the Martian surface captured in the 1960s by the Mariner IV space probe confirmed Tombaugh's prediction.

In 1946, Tombaugh began a relatively brief career as a civilian employee of the U.S. Army, working as an optical physicist and astronomer at White Sands Proving Grounds near Las Cruces, New Mexico, where the army was developing launching facilities for captured German V-2 missiles. Tombaugh witnessed 50 launchings of the 46-ft (14-m) rockets and documented their performance in flight using a variety of tracking telescopes. Armed with his observing skills and intimate knowledge of telescope optics, Tombaugh greatly increased the quality of missile tracking at White Sands, host to a number of important postwar missile-development programs.

Tombaugh resumed serious planetary observing in 1955, when he accepted a teaching and research position at New Mexico State University in Las Cruces. There, he taught astronomy, led planetary observation programs, and participated in the care and construction of new telescopes. From 1953 to 1958, Tombaugh directed a major search for small, asyet-undetected objects near the Earth—either asteroids or tiny natural satellites—that might pose a threat to future spacecraft. He and colleagues developed sensitive telescopic tracking equipment and used it to scan the skies from a high-altitude site in Quito, Ecuador. The survey turned up no evidence of hazardous objects near Earth, and Tombaugh issued a closing report on the program the year after the Soviet Union launched Sputnik (1957), the first artificial satellite .

Upon his retirement in 1973, Tombaugh maintained his links to New Mexico State University, often attending lunches and colloquia in the astronomy department that he helped to found. He also remained active in the local astronomical society and continued to observe with his homemade telescopes. Indeed, asked by the Smithsonian Institution in Washington, D.C., to relinquish his 9-in reflector to its historical collections, Tombaugh refused, explaining to Smithsonian magazine, "I'm not through using it yet!" He died in 1997 at his home in Las Cruces, New Mexico.