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The Pluto Discovery telescope.

The Pluto Discovery telescope.

The Pluto Discovery Telescope

Built in 1928-1929 expressly for the purpose of completing the search for “Planet X” – the name for the hypothetical ninth planet in the solar system that Percival Lowell thought must exist – the Pluto Discovery Telescope, like the Clark, is one of the most famous telescopes in the history of American astronomical research.

Known as an astrograph (or astrographic camera), the telescope has three lenses, each 13 inches (32.5 cm) in diameter. The light from (or reflected off) a celestial object was focused onto a 14″ x 17″ (35 cm x 42.5 cm) glass photographic plate. Time exposures of about an hour were made for each image. The glass negatives were then scrutinized using the Zeiss blink comparator, which is currently on loan to the Air and Space Museum in Washington D.C.

Reviewing a set of glass negatives on February 18, 1930, Observatory assistant Clyde Tombaugh made the first recognized sighting of the object later named Pluto.

After the discovery of Pluto, Henry Giclas used the telescope for his proper-motion survey, in which he studied the actual (not just apparent) motion of celestial objects. The telescope was later moved to the Observatory’s Anderson Mesa dark-sky site and then returned to Mars Hill in the early 1990s so our visitors could see this historic instrument first-hand.

Principal funding for the instrument and dome came from Abbott Lawrence Lowell, Percival’s younger brother and then president of Harvard University.

For a detailed history about the Pluto Telescope, read The 13-inch Pluto Discovery Telescope (PDF).


The telescope that Clyde Tombaugh used to discovery the icy world in 1930 was in need of care. Our team did an incredible job on the restoration of the 120-year-old Clark refractor and they gave the same attention to this historic instrument. The restoration process included removal and restoration of the telescope, structural work, exhibit renovation, and dome removal and repair.

Pluto Telescope Restoration Press Release

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