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The Clark Telescope at Lowell Observatory


The Clark Telescope is closed for renovations from January 1, 2014 through mid-2015. Daytime Deep Space Tours will still generally go inside of the dome. In the evening, we will use the recently renovated 16-inch McAllister Telescope as our primary telescope for public viewing.

JANUARY 1, 2014 CLARK RENOVATION OVERVIEW - In 1895, Lowell Observatory founder Percival Lowell commissioned the Alvan Clark & Sons Firm of Cambridgeport, Massachusetts to build a state-of-the-art 24-inch refracting telescope. Since completion of the project the following year, the telescope has been in regular use to view the heavens and help unravel the wonders of the universe. The facility is now undergoing a renovation requiring disassembly of the telescope and replacement of parts no longer functioning properly.

The Clark Telescope is one of seven structures listed in the Observatory's 1964 Registered National Historic Landmark designation. In 1999, First Lady Hillary Clinton recognized Lowell Observatory and, specifically, the Clark, as a site worthy of preservation as part of her Save America's Treasures program.

Percival Lowell initially used the telescope to further his legendary theories about intelligent life on Mars, research that brought worldwide attention to Lowell Observatory. Percival's elegant writings about his research, based on observations made with the Clark Telescope, inspired the work of both scientists, such as rocket expert Robert Goddard, and writers, including science fiction icons H.G Wells and Edgar Rice Burroughs.

Later generations used the Clark Telescope to study double planets, moons, comets, and more. Of particular note, V.M. Slipher revolutionized our understanding of space with his observations of the expanding nature of the universe. He made these fundamental discoveries while using the Clark Telescope in conjunction with an instrument called a spectrograph, a device astronomers use to not only determine the composition of celestial objects, but also detect their line-of-site-motion.

In the 1960s, a team of scientists and artists used the Clark Telescope to create detailed maps of the moon in support of America's manned voyages to the moon. Apollo astronauts studied these maps and some even used the Clark Telescope for part of their training to go to the moon.

By the 1980s, education replaced research as the primary use of the Clark Telescope. Since then, more than two million guests have had the opportunity to enjoy the telescope by joining daytime historic tours or viewing celestial objects during the evening. In 2013, 75,000 people - including 7,500 school children - visited the facility.

In 2012, Lowell launched our Kids Camp for 1st-6th grade students and in 2013 added Tykes Camp for 3-5 year-olds. We are now planning an ambitious long-range plan to establish the Observatory as a center for STEM (Science Technology, Engineering and Mathematics) education. The Clark Telescope is critical to the long-term success of these endeavors.

Over the past several years, the telescope has become more and more difficult to move, due to the degradation of the main support bearing in the optical tube. If this problem were to continue, the telescope would become inoperable. To avoid this outcome, we will remove (using a crane) and dismantle the optical tube and repair of replace the main bearing and other faulty parts, most of which will be fabricated in-house.

We will also install an updated tracking device that will allow the Clark to accurately follow celestial objects as they wander across the skies and clean all components, including the primary lens, optical tube and pier. If necessary, we will strip and recoat the pier.

As for the dome, old wiring is a significant safety issue. We will thus replace all existing wiring, as well as switch gear and load center. We will also replace the shutter doors, which no longer operate properly on a regular basis. Additionally, we will repair metal siding, particularly in areas where snow and rain enter the dome, and refinish the floor.

Most of the work done will be done onsite so visitors can see progress first-hand. We will then host a dedication and grand reopening of the telescope sometime in 2015.

Our fundraising effort, highlighted by major donations from the Toomey Foundation for the Natural Sciences. and the late Joseph N. Orr, will cover the cost of the essential restoration work. If you would like to support other Clark-related efforts, particularly for educational exhibits, please call Antoinette Beiser at (928) 233-3216.

APRIL 2013 CLARK TELESCOPE TO BE RENOVATED - Thanks to donations from many generous supporters, we are preparing to restore the 24" Alvan Clark refractor, a national treasure in need of significant restoration. Stay tuned to this page for updates on our progress.

Presently still in use for nighttime viewing by our public visitors, the Clark Telescope arrived new in 1896 and was the first permanent telescope at Lowell Observatory. The Clark is one of the largest, most productive telescopes of its era and the first large telescope in the desert southwest of the United States.

This telescope was manufactured by the Alvan Clark & Sons Company from Cambridgeport, MA. Mr. Clark himself ground the two 24-inch (61-cm) diameter lenses; this set of optics is still one of the finest made in this epoch, and is especially effective for the study and observation of planets. The telescope tube is 32 feet (10 m) in length, made of rolled steel, and with the other moving parts weighs six tons (5400 kg). Despite the weight, this telescope is so well balanced that it is easily moved by hand!

Percival Lowell was, of course, the first to conduct research with the Clark, closely examining the surface of Mars; his books about this research helped popularize the "Red Planet" and astronomy as a whole among the general public. V.M. Slipher utilized the Clark for his seminal galaxy research, the most impactful research ever conducted at Lowell. Slipher was the first to detect the radial velocities of galaxies, a discovery which led to the realization that the universe is expanding and set the stage for the "Big Bang" theory.

From 1961 to 1969, U.S. Air Force and Lowell cartographers made detailed maps of the moon based on observations made with the Clark Telescope. These maps were critical to the Apollo program, during which men landed on and studied the moon's surface. Today, the Clark is no longer used for research but is part of our Mars Tour and special programs, and is used for nighttime viewing, weather permitting.

The Clark's dome is made of local Ponderosa pine wood and was constructed in Flagstaff. The dome, weighing eight tons (7300 kg), sits on 24 replica 1954 Ford pickup tires and is rotated by three electric motors.

 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