One mile west of downtown Flagstaff, on a pine-covered mesa called Mars Hill, sits one of the most consequential astronomical research sites in American history. Lowell Observatory has been operating continuously since 1894 — founded by Boston mathematician and astronomer Percival Lowell, who came to the Arizona Territory specifically for its clear, dark skies and high elevation. What he started here changed our understanding of the universe in ways that are still being felt.

Our Visits

March 2011 — Alexis with Herman and Elfriede

Alexis visited Lowell Observatory with Herman and Elfriede in March 2011 — their photos and experience are part of this record. A spring visit to Flagstaff with the observatory as the centerpiece.

May 16, 2022 — Luca, Rachel, and Parents

Part of a Flagstaff stay that also included the Museum of Northern Arizona and Walnut Canyon National Monument — a full northern Arizona cultural day that covered astronomy, Indigenous history, and ancient cliff dwellings in a single visit sequence.

We attended a program where the presenter used special glasses that revealed rainbows — spectroscopy glasses that split white light into its component wavelengths, showing the full visible spectrum. The same principle revealed through fire — the presenter burned different compounds to display the distinctive colors each element produces when combusted. Sodium burns yellow. Copper burns green. Potassium burns violet. Each element has a unique spectral fingerprint — and this is precisely how astronomers determine the composition of stars and planets millions of light years away. You can't send a probe to a distant star, but you can read its light. Watching that demonstrated with fire and colored glasses in real time made one of astronomy's most fundamental tools immediately and viscerally understandable.

We visited and viewed through all the public telescopes available on the grounds. Attended a star party on the Giovale Open Deck Observatory — the open-air platform with multiple telescopes where astronomers guide visitors through the night sky, pointing out planets, star clusters, nebulae, and the features that make Flagstaff's dark sky one of the finest in the American Southwest for public stargazing.

The Historic Clark Telescope Dome

The dome that houses the 24-inch Clark Refractor Telescope is one of the most distinctive structures on Mars Hill — and one of the most memorable things to see at Lowell regardless of what else you do there. The dome itself is historic and unusual: rather than rotating on a modern motorized track, it moves on a system of wooden wheels — the original 1896 mechanism still functional after more than 125 years. The entire dome rolls on these wooden wheels when the telescope needs to be repositioned, the wood creaking and the dome turning with a weight and deliberateness that speaks to the craftsmanship of the era. Standing inside while the dome moves is a different relationship with the history of the instrument than reading about it.

The Clark Telescope inside the dome is a 24-inch refractor built by Alvan Clark & Sons of Massachusetts — the finest telescope makers of the 19th century. The same instrument Vesto Slipher used in 1912 to detect the first evidence of the expanding universe. It has been in continuous use for over 125 years. That it still operates — that the original dome mechanism still rolls on its original wooden wheels — is a remarkable piece of preserved scientific heritage.

We saw the exhibits at the Astronomy Discovery Center and the Rotunda Museum — the historical collection, the instruments, and the interpretive materials that place Lowell's discoveries in the context of the history of science. The Rotunda in particular — the original library at the heart of the observatory campus — connects the physical space to the people who worked here.

Percival Lowell and the Observatory's Founding

Percival Lowell was a wealthy Boston aristocrat who gave up a career in business and diplomacy to pursue astronomy full time. He was convinced that Mars was inhabited by an intelligent civilization — his detailed drawings and writings about Martian canals became famous and controversial in equal measure. Most professional astronomers rejected his Mars theories, but his passion for the night sky was genuine and his choice of Flagstaff for his observatory was scientifically sound. He arrived in 1894, chose Mars Hill for its elevation of 7,200 feet and its reliably clear and dark skies, and began building.

The observatory Lowell founded is named for him and sits today on the same hill where he built his first telescope dome. His mausoleum — a beautiful blue domed structure — sits adjacent to the Clark Telescope dome, within sight of the instrument he used for his Mars observations. He is buried on the hill where he spent his most productive years.

The Expanding Universe — 1912

In 1912 Lowell Observatory astronomer Vesto Melvin Slipher used the 24-inch Clark Telescope to measure the radial velocities of spiral nebulae — what we now call galaxies. His measurements showed that most galaxies were moving away from Earth at enormous speeds. This was the first observational evidence that the universe is expanding — one of the most significant discoveries in the history of science. Slipher's data was later used by Edwin Hubble to formulate Hubble's Law. The Clark Telescope that made this discovery is still on Mars Hill and still used for public viewing.

The Discovery of Pluto — 1930

Percival Lowell had predicted the existence of a ninth planet — a "Planet X" — whose gravitational influence he believed was affecting the orbits of Uranus and Neptune. He spent years searching for it without success and died in 1916 still looking. The search continued after his death. In 1929 the observatory hired a 23-year-old Kansas farm boy named Clyde Tombaugh to continue the search using a new 13-inch astrograph — a telescope specifically designed for photographing large areas of sky.

On February 18, 1930, Tombaugh compared photographic plates taken on January 23 and 29 and noticed a faint point of light that had moved between the two exposures — exactly as a planet would. He had found Pluto. The discovery was announced on March 13, 1930 — the 75th anniversary of Percival Lowell's birth and the 149th anniversary of William Herschel's discovery of Uranus.

The name Pluto was suggested by Venetia Burney, an 11-year-old British schoolgirl who proposed the name of the Roman god of the underworld for the cold, distant, dark world. The first two letters — PL — were also the initials of Percival Lowell, a connection that was not lost on the observatory. Pluto was classified as the ninth planet until 2006 when the International Astronomical Union redefined the criteria for planethood and reclassified it as a dwarf planet — a decision that remains contentious among astronomers and the general public alike.

The 13-inch Pluto Discovery Telescope is still at Lowell Observatory and open to visitors in the Pluto Discovery Dome — one of the most remarkable pieces of scientific heritage accessible to the public anywhere in the United States.

The Moon and Apollo

In the 1960s NASA partnered with Lowell Observatory to help prepare for the Apollo program — astronomers here mapped the lunar surface and helped familiarize astronauts with the features they would encounter on landing. The 24-inch Clark Telescope played a role in this preparation. The connection between a 19th-century research telescope and the Moon landings is one of the more unexpected threads in Lowell's history.

The Rings of Uranus — 1977

On March 10, 1977, Lowell Observatory astronomers were observing Uranus from the Perth Observatory in Australia when they discovered that the planet has rings — nine of them at the time of discovery, later expanded to 13. This placed Lowell Observatory in the company of the three solar system discoveries made here — the expanding universe, Pluto, and the rings of Uranus.

What to See and Do

Astronomy Discovery Center — the main visitor building with interactive exhibits on the history of the observatory, the science of astronomy, and the major discoveries made here. The Putnam Collection Center lobby displays select items from the observatory's historical collection.

The Clark Telescope — the 24-inch refractor built in 1896 and still operational. Guided tours visit the Clark dome — standing inside it and looking through the same instrument that detected the expanding universe in 1912 is a genuinely remarkable experience. Used for public viewing on clear nights.

Pluto Discovery Dome — the historic building where Clyde Tombaugh discovered Pluto in 1930. The 13-inch Lawrence Lowell Telescope that made the discovery is inside. Educators on hand to answer questions and share the story of one of astronomy's most famous moments.

Rotunda Library Museum — the historic library at the heart of the original observatory campus.

Dark Sky Planetarium — 360-degree above-the-treetops views of Flagstaff's skies from the crown of the Astronomy Discovery Center.

Solar System Walk — a scale model walk connecting the visitor center to the Pluto Discovery Telescope — the distances along the walk represent the relative distances of the planets from the Sun.

Percival Lowell's Mausoleum — the blue domed structure adjacent to the Clark Telescope dome where Lowell is buried. Open to visitors on the observatory grounds.

Nighttime Stargazing — the primary evening experience. The open-air amphitheater with heated seats offers guided constellation tours and telescope viewing on clear nights. Flagstaff is an International Dark Sky City — the darkness of the skies above Mars Hill is exceptional for a city location. Jupiter, Saturn, star clusters, and nebulae visible through the observatory's telescopes on a clear night.

Daily Tours and Programs

Lowell Observatory offers guided daytime tours covering the Story of Pluto and the Pluto Discovery Telescope, the historic Clark Telescope and Rotunda Library, and evening constellation tours with telescope viewing. A full schedule of current tour times and nighttime programs is available at lowell.edu — check before your visit as times vary by season. Reservations are recommended for evening programs which fill quickly on clear nights.

The Connection to Kitt Peak

If you've visited Kitt Peak National Observatory south of Tucson — as we have — Lowell Observatory on the same trip creates a remarkable context for understanding Arizona's role in astronomical history. Both sites chose Arizona for the same reasons Percival Lowell did in 1894 — elevation, clear skies, and darkness. The state has been at the center of American astronomical research for over 130 years.

Contact

Lowell Observatory1400 W. Mars Hill Road, Flagstaff, AZ 86001

(928) 774-3358

lowell.edu

Hours (2026)

Daily 10:00 AM — varies by season and program

Check lowell.edu for current hours and nighttime program schedules

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