Clyde W. Tombaugh

American astronomer

• Born: February 4, 1906; Streator, Illinois
• Died: January 17, 1997; Las Cruces, New Mexico

Clyde W. Tombaugh discovered the dwarf planet Pluto and several star clusters and galaxies, studied the distribution of extragalactic nebulas, searched for small natural Earth satellites, and made observations of the surfaces of several planets and of Earth’s moon.

Primary field: Astronomy

Specialty: Observational astronomy

Early Life

Clyde William Tombaugh was born in Streator, Illinois, on February 4, 1906. His parents, Muron and Adella Tombaugh, operated a farm. In high school, Tombaugh became a voracious reader, devoting many hours to encyclopedias and books on mathematics and physics. His uncle, an amateur astronomer, gave him books on astronomy. Tombaugh’s interest in astronomy was further stimulated in 1920 when his father and uncle bought a small refracting telescope. This eventually became Tombaugh’s first telescope, and he later installed it as a finder on a sixteen-inch telescope.

A poor corn crop in 1921 led the Tombaughs to move to a farm near Burdett, Kansas, where they took up wheat farming. After the harvest of 1925, Tombaugh began the tedious process of grinding and polishing a mirror for an eight-inch reflecting telescope. After sending the mirror away for silvering, he was disappointed to learn that it had a poor figure and would not work well. He then built a testing chamber for mirrors in a family tornado cellar and began working on a seven-inch mirror for his uncle, with much better results. In 1928, he completed a nine-inch reflecting telescope for himself and began serious observation.

Tombaugh’s plans to attend Kansas State University in the fall of 1928 were thwarted by a summer hailstorm that destroyed the crops. Seeking advice, he mailed his best astronomical sketches to Lowell Observatory in Flagstaff, Arizona. Observatory director Vesto Slipher, who was seeking to hire a dedicated amateur astronomer to operate a new photographic telescope for a long-exposure survey of the sky, offered Tombaugh a job. In January 1929, Tombaugh traveled to the observatory for a ninety-day trial period.

Life’s Work

Tombaugh’s work at Lowell Observatory built upon the predictions of astronomer Percival Lowell, who had proposed in 1905 that an unknown object he called Planet X might cause the apparent discrepancies in the orbit of the planet Uranus, which had been discovered in 1781. The study of small deviations in Uranus’s orbit had led to the discovery of Neptune in 1846, but the orbital motion of Uranus did not appear to be totally explained by Neptune’s presence. Therefore, Lowell postulated the existence of Planet X and initiated a series of unsuccessful searches at his observatory in Flagstaff.

Lowell died in 1916, and further searches were delayed when his widow challenged his will, which had designated funds for the Lowell Observatory. After the suit was settled a decade later, a new thirteen-inch refractor telescope and wide-angle camera were built. Tombaugh’s first duties after arriving in Flagstaff on January 15, 1929, included painting the new telescope, stoking the furnace, removing snow from the observatory domes, giving tours for visitors, and training for the planet search that began in earnest on April 26.

After months spent photographing the sky and analyzing the resulting photographic plates, it occurred to Tombaugh that a new planet could best be identified when it was near its opposition point, 180 degrees from the sun. He also began to look at new regions of the sky rather than concentrating on the predicted positions that Lowell had calculated. On February 18, Tombaugh observed an object in the photographic plates that he believed could be Planet X. The observatory announced the discovery of a new planet on March 13, 1930, the seventy-fifth anniversary of Lowell’s birth. Six weeks later, on May 1, Slipher proposed the name Pluto for the planet, after the Greek god of the underworld, and a superposed P on L was chosen as its symbol, matching the initials of Percival Lowell.

For the next two years, Tombaugh continued his search to be sure that no other planets might be missed. On June 1, 1932, he made his second major discovery when he identified a globular cluster of stars in the Milky Way Galaxy’s central hub. In the fall of 1932, Tombaugh was given a leave from the observatory to study at the University of Kansas, from which he earned a degree in astronomy in 1936. While a student, he met Patricia Edson, whom he married in 1934. Returning to Flagstaff, he continued his sky survey until 1943, pausing only to complete his master’s degree in Kansas. In 1937, he discovered a supercluster of galaxies and measured its shape and size, eventually cataloging nearly thirty thousand galaxies. He found five open star clusters and identified nearly four thousand asteroids, of which more than seven hundred had not been observed before.

In 1943, Tombaugh began teaching physics and navigation for the US Navy at Northern Arizona State Teachers College in Flagstaff. In 1946, he moved to Las Cruces, New Mexico, to take a position at the White Sands Proving Ground. There, he designed optical equipment and supervised the tracking of V-2 missile firings. In 1953, he received military funding to search for small natural Earth satellites, and for the next two years, he divided his time between White Sands and Lowell Observatory, where the search began.

In 1955, Tombaugh transferred the natural satellite search project to New Mexico State University to facilitate observations from Quito, Ecuador. No such satellites were discovered, but in 1957, Tombaugh and his team took some of the first photographs of Sputnik, the first artificial satellite, and provided the observational basis for the safety of an extensive artificial satellite program. From 1955 to 1973, he was a professor in the Department of Earth Sciences and Astronomy at New Mexico State University, where he established a comprehensive observational program of the five nearest planets.

Tombaugh remained active in astronomy after his retirement in 1973, continuing to build telescopes. Over his lifetime, he ground more than thirty optical surfaces and built many telescopes. Telescopes on which he worked were later featured at the observatories at New Mexico State University and the University of Kansas, both of which were named in his honor. Tombaugh died in Las Cruces, New Mexico, on January 17, 1997.

Impact

Over time, scientists determined that Lowell’s predictions for the position of Pluto were based on faulty calculations, and its discovery near the predicted location was only a coincidence. It was conclusively demonstrated that the mass of Pluto was far too small to cause observable deviations in the orbits of Uranus and Neptune; thus, the two larger planets’ orbits could not be used to predict Pluto’s position. Tombaugh’s decision to search for the planet beyond the coordinates predicted by Lowell, then, proved to be crucial to its discovery. For his contributions to the field of astronomy, Tombaugh was awarded the Jackson-Gwilt Medal by the Royal Astronomical Society in 1931.

By the early twenty-first century, several icy objects were discovered beyond Pluto’s orbit, in the area known as the Kuiper Belt. The objects have orbital periods of more than 300 Earth years, compared to Pluto’s 248-year period. In 2006, the International Astronomical Union grouped Pluto with other large Kuiper Belt objects, classifying them as “dwarf planets.” Because Pluto is extremely difficult to observe from Earth, NASA launched its New Horizons spacecraft in 2006 with the goal of studying Pluto in depth during the craft’s flight past in 2015 and observing several other Kuiper Belt objects when the craft travels farther out into space.

Bibliography

Adler, Larry, Mary Carmichael, Nomi Morris, and A. Christian Jean. “Of Cosmic Proportions.” Newsweek 148.10 (2006): 44–50. Print. Includes discussion of Tombaugh’s discovery of Pluto and examines how and why Pluto lost its planetary status and how that decision changed the shape of the solar system.

Levy, David H. Clyde Tombaugh: Discoverer of Planet Pluto. Tucson: U of Arizona P, 1991. Print. Provides a complete biography of Tombaugh, written by a fellow astronomer and based on thorough research and personal interviews.

Tombaugh, Clyde W., and Patrick Moore. Out of the Darkness: The Planet Pluto. Harrisburg: Stackpole, 1980. Print. Provides an extended account of the discovery of Pluto, written for the fiftieth anniversary of its discovery, with background information on asteroids, Uranus, and Neptune.

Weintraub, David A. Is Pluto a Planet? A Historical Journey through the Solar System. Princeton: Princeton UP, 2007. Print. Examines how the definition of a planet has changed throughout history and chronicles how Pluto’s claim to planetary status has been challenged in the decades since its discovery.