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Learn about the Discovery Channel Telescope
The Pluto Telescope

The Pluto Telescope at Lowell Observatory

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 now resides in the Rotunda Museum.

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.

 Visitor Info


Covers day and evening programs; reservations not needed.

Adults: $12

Seniors, AAA, college students: $11

Ages 5–17: $6

Under 5: Free

Members: Free

For general questions about our day and evening programs, call the Visitor Center at (928) 233-3212 during open hours (listed below).

Groups of 15 or more are eligible for a group discount; to qualify, you must make reservations at least 3 weeks in advance. Contact Samantha Flagg by email or phone at 928-856-9484.

2015 Hours

Monday through Saturday
10 a.m. - 10 p.m.

10 a.m. - 5 p.m.

Arizona observes Mountain Standard Time year round.
Click here
for the current time in Flagstaff, AZ.

Extended Hours in 2015

Feb 15, 2015 - Open until 10 p.m.

Special Closures in 2015

Jan 1, 2015 - Closed all day

Nov 26, 2015- Closed all day

Dec 25, 2015 - Closed all day