Press Release

Discovery of Pluto Reaches 75th Anniversary

By SpaceRef Editor
February 5, 2005
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Discovery of Pluto Reaches 75th Anniversary

Flagstaff, AZ–The planet Pluto turns 75 this month. Clyde Tombaugh discovered the ninth planet in the solar system on the afternoon of February 18, 1930 while he meticulously examined a pair of deep sky photographs at Lowell Observatory. Tombaugh exposed the photographs on two nights in late January using the Observatory’s 13-inch Abbott Lawrence Lowell Telescope. Then, as part of the carefully planned and executed planet search, Tombaugh “blinked” the two exposures using a machine called a comparator, looking for motion of objects captured on film.

“One need only visit Lowell Observatory and view copies of the discovery images through the same eyepiece used by Clyde Tombaugh to appreciate what a remarkable discovery this was,” said Bob Millis, Director. “The images are extremely faint and testify to the skill, concentration, and dedication that Clyde Tombaugh brought to his work.”

Lowell Observatory’s search for a ninth planet was begun by founder Percival Lowell in 1905. While Dr. Lowell did not live to see the discovery of Pluto, the Observatory made the official announcement of the discovery on Percival Lowell’s birth date, March 13, 1930. After many suggestions, Pluto was selected as the name for the new planet. As an added plus, the astronomical community adopted a symbol for the planet that also was a combination of Percival Lowell’s initials. Eleven-year-old Venetia Burney from Oxford, England suggested the name.

Several Lowell Observatory astronomers continue to study Pluto, including Marc Buie and Will Grundy. Marc Buie has studied the cold, dark outer regions of the solar system —with a special interest in Pluto —since the early 1980s. Buie is conducting a long-term project to monitor Pluto’s brightness changes on decade, or longer, time scales. One of his recent, ongoing projects is aimed at producing a new generation of Pluto maps based on images taken with the Hubble Space Telescope. Buie has developed a small, high-performance computing cluster for this project at the Observatory.

Will Grundy, Lowell Associate Astronomer, studies icy surfaces of outer solar system objects including Pluto, the icy satellites of giant planets, centaurs, and Kuiper Belt Objects. Grundy is a science team member on NASA’s New Horizons: A Pluto-Kuiper Belt Mission.

“In the past decade, we have progressed from thinking of Pluto as a barely resolved 14th magnitude point of light to seeing it as a unique world with complicated seasonal cycles and with surface regions exhibiting diverse appearances and chemical compositions,” Grudy said.

To complement the astronomy research that includes these ongoing Pluto studies, Lowell Observatory maintains an active educational and outreach program. The Observatory will present a Pluto 75th anniversary program on the evening of Friday, February 18 as part of its regular evening programs. The nighttime program consists of a special Cosmic Cart at 7:45 p.m., a series of demonstrations particularly suitable for children. This will be followed by a lecture about Pluto at 8:30 p.m. The Observatory opens at 7:30 p.m. and telescope viewing will occur throughout the evening, weather permitting. For more information, visit

In addition to its Pluto research, Lowell Observatory has ongoing and long-term programs to identify near-Earth asteroids, survey a region of the solar system beyond Neptune known as the Kuiper Belt, conduct decades-long research on the sun and sun-like stars, study comets, search for extrasolar planets, and pursue a variety of astrophysical investigations. The Observatory is also building the Discovery Channel Telescope, a partnership with Discovery Communications that will produce a versatile, powerful 4.2-meter telescope.

Lowell Observatory’s mission is to pursue the study of astronomy, especially the study of our solar system and its evolution; to conduct pure research in astronomical phenomena; and to maintain quality public education and outreach programs to bring the results of astronomical research to the general public. The Observatory was founded in 1894. Visit


[This press release is also online at:]

For media, Internet resources: Historic Pluto discovery photographs from Lowell Observatory archives are posted at: (see contact for permissions, credits, caption information, etc).

Also, the Lowell Observer, an online version of the Observatory’s quarterly newsletter features two Pluto articles:

New Horizons: A Pluto-Kuiper Belt Mission:

NASA NSSDC Pluto page

SpaceRef staff editor.