In 1930, a young astronomer named Clyde Tombaugh was scrutinizing photographic plates in a red brick building perched on Mars Hill, in Flagstaff, Arizona. By comparing images of the night sky taken days apart, he noticed a bright dot that was moving: it was Pluto. That building still exists today, and visitors can enter the same space, look through the same instruments, and touch — almost — the history of modern astronomy.
The Lowell Observatory was founded in 1894 by the astronomer and philanthropist Percival Lowell, who was convinced that Mars hosted intelligent civilizations and determined to prove it with a top-notch telescope. He chose Flagstaff not by chance: the altitude of about 2,100 meters above sea level and the clear skies of the Arizona plateau ensured exceptional observing conditions. That choice proved prophetic: today Flagstaff is recognized as the first International Dark Sky City in the world, a title that legally protects the darkness of its night skies.
The Clark Telescope and the Historic Dome
The beating heart of the observatory is the 24-inch Clark refractor (about 61 centimeters in aperture), installed in 1896 and still perfectly operational. The instrument was built by the renowned company Alvan Clark & Sons from Massachusetts, the same craftsmen who created some of the largest refractors of the Victorian era. The wooden dome that houses it creaks reassuringly when it rotates, powered by an original mechanism that seems to have come straight out of a Jules Verne novel.
During the evening sessions open to the public — organized almost every night when the weather permits — guides accompany visitors inside the dome and allow them to put their eye to the eyepiece of the Clark. With good atmospheric conditions, it is possible to observe lunar craters, Saturn's rings, or nebulae, through the same instrument that Percival Lowell used to draw his maps of Mars. It is an experience hard to replicate elsewhere: few historic observatories in the world still offer direct access to a fully operational 19th-century telescope.
The visitor center and the history of Pluto
The modern Steele Visitor Center, inaugurated in 2015, hosts interactive exhibits that tell the story of the observatory with scientific rigor and good narrative ability. One section is entirely dedicated to the discovery of Pluto: you can see reproductions of the original photographic plates used by Tombaugh and the Blink Comparator, the optical instrument that allowed for the rapid alternation of two images to identify moving objects. The comparison with the original plates makes it immediate and almost exciting to understand how the planetary search method worked before the digital era.
The exhibition path also includes insights into the current work of the observatory, which is not a museum frozen in time but an active research institute. The astronomers at Lowell participate in international programs studying objects in the outer solar system and distant galaxies. This dual nature — historical heritage and living laboratory — is perhaps the most interesting characteristic of the place.
Practical tips for the visit
The best time to visit the Lowell Observatory is in the late afternoon, arriving about an hour before sunset: this allows time to calmly explore the visitor center and the wooded campus trails before the evening program begins. The night sessions with the Clark telescope generally last until around 10:00 PM and are included in the entrance ticket, which costs around 20-25 dollars for adults (always check the official website for updated rates and availability, as some themed evenings may require separate reservations).
The observatory is located just a few minutes from downtown Flagstaff, accessible by car following the signs to Mars Hill Road. There is not a huge parking lot, so it is advisable to arrive early on summer weekends. Bring a sweater even in summer: at over 2,000 meters in altitude, the nights cool down quickly, and waiting your turn at the outdoor telescope can take several minutes. Those who are sensitive to the cold will still find refuge in the heated visitor center. Finally, avoid using white light flashlights during night sessions: the guides provide red light flashlights to preserve the eyes' adaptation to darkness, a small consideration that radically changes the quality of observation.
