Clyde Tombaugh, 1906 - 1997

 [Clyde Tombaugh]

The only 20th century Solar System planet discoverer, he died at age 90 on Friday, January 17, 1997, in his home in Las Cruces, New Mexico. He was with Patsy, his wife for more than 60 years.

Discoverer of dwarf planet Pluto:

Clyde Tombaugh, born in Streator, Illinois, in 1906, moved with his family to a farm near Burdett, Kansas, during his high school years.

He shared his father's keen amateur interest in astronomy, and when he wanted a telescope more powerful than his 2 1/4-inch Sears Roebuck model, he began grinding mirrors and making his own.

On his father's Kansas farm he built his own 9-inch reflector, using parts from a cream separator for the mount. Another mount component was a part of the crankshaft from his father's 1910 Buick.

He used this telescope to make fine sketches of Mars and Jupiter, and sent the drawings to the Lowell Observatory, for comment (they are still there today), he was offered a job as an assistant.

The astronomer Percival Lowell, at his private Observatory in Flagstaff, Arizona, instituted in 1905 a search for an unknown planet beyond Neptune, the cause of slight perturbations in the motions of Uranus.

Working through the nights in a cold, unheated dome, he made pairs of exposures of portions of the sky with time intervals of two to six days.
These were scrutinized under a device called a Blink-Comparator in hopes of detecting a small shift in position of one of the hundreds of thousands of points of light -- the sign of a planet among a field of stars.

Due to Tombaugh's efforts and the backing of the director Vesto M. Slipher, this search resulted in his photographic discovery of Pluto on February 18, 1930.
At that time, he found Pluto as a faint (magnitude 17), slowly moving spot in the constellation of Gemini.

The new planet's mass, however, seemed insufficient to account for the perturbations of Neptune, and the search for a possible tenth planet continued.

Tombaugh continued searching the skies at Lowell Observatory over the next 13 years, with time out for a college education. No more planets showed up, but he discovered six star clusters, two comets, hundreds of asteroids, several dozen clusters of galaxies and the super-cluster of galaxies stretching from Andromeda to Perseus. In 1932 he discovered a nova in Corvus that had exploded a year earlier.

Tombaugh obtained degrees from the University of Kansas (1936 and 1939) and Arizona State University (1960), he went to work at New Mexico's Aberdeen Ballistic Laboratories Annex in 1946 to become chief of the Optical Measurements Branch at White Sands Missile Range, where German V-2 rockets were being tested.
He joined the faculty of New Mexico State University in 1955, and started the Planetary Group, an astronomy research program. He reached the status of Professor Emeritus in 1973.

By the time he retired, he and his NMSU astronomy staff had confirmed the rotation period of Mercury on its axis, determined the vortex nature of Jupiter's Great Red Spot, and developed a new photographic technique for the small Earth satellites search he was supervising.

After retiring in 1973, Clyde maintained a very active profile, giving lectures frequently. Between 1985 and 1990 he crisscrossed the continent, giving lectures to raise funds for the Tombaugh Scholars program at New Mexico State.

Clyde Tombaugh was always accessible to amateur astronomers, and generously shared detailed advice about observing in countless letters written in long hand.


The ninth and usually most distant planet from the Sun, is the smallest and most remote planet in the Solar System, at a mean distance of 5,900 million Km (3,670 million miles).
The planet was named for Pluto, god of the underworld in Roman mythology, Pluto assisted his two brothers, Jupiter and Neptune, in overthrowing their father, Saturn.

Pluto has a sidereal period of revolution about the Sun of 247.7 years, 4,500 million kilometers (2,800 million miles) distant at perihelion and 7,400 million kilometers (4,600 million miles) at aphelion.
Because of the high eccentricity (0.250) of its elliptical orbit, Pluto occasionally (e.g., between Nov. 28, 1978 and February 11, 1999) comes closer to the Sun than the planet Neptune.
No possibility of collision exists, however, because Pluto's orbit is inclined more than 17.2° to the plane of the ecliptic and never actually crosses Neptune's path.

Pluto has a diameter of 2,320 Km (1,440 miles). Its surface consists largely of frozen nitrogen. It is thought to have a rocky, silicate core, its thin atmosphere is thought to contain methane.
Pluto forms a double planet system with its one known satellite, Charon, which has a diameter of 1,270 Km (790 miles), about half of Pluto's. Charon was discovered by James Christy in 1978.

Photo by R. Sterling Trantham


STScI: Pluto and Charon (Hubble Space Telescope)
Clyde Tombaugh (1906-1997) (by Jeff Foust)

Pluto is now a "dwarf planet" by The IAU definition of "planet" and "dwarf planets" (August 24 '06).
See Observatorio ARVAL: Solar System Data, Hubble Views the Pluto System, New Hubble Maps of Pluto Show Surface Changes.

On 13 September '06 the IAU Minor Planet Center assigned to Pluto the asteroid number 134340.
See IAU Minor Planet Center Circular 8747.

Updated: September 15 '06, April 16 '10, June 24 '14

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