24-inch Clark Telescope
Built in 1896, the Clark Telescope is named after its builder, Alvan G. Clark of the Alvan Clark & Sons Corporation. The 24-inch refractor was one of Lowell Observatory's first instruments and Percival Lowell's primary telescope for observing Venus and Mars. It arrived in Flagstaff by train in early July 1896. Lowell, assisted by A.E. Douglass, W.A. Cogshall, T.J.J. See, Wrexie Leonard, and Daniel Drew, installed the telescope and began making observations within a month.
Due to the typical nature of Flagstaff's weather, Lowell was unhappy with viewing conditions and with the help of Douglass, found a site in Tacubaya, Mexico where they moved the telescope in December of 1896. Eventually, Lowell came to find he didn't like the conditions in Mexico and the remoteness of the site and moved the Clark back to Flagstaff in April of 1897.
Lowell Observatory astronomers used the Clark as a research instrument for decades. V.M. Slipher used a spectrograph mounted on the telescope to discover the redshift of galaxies, which laid the foundation for the discovery of the expanding universe. E.C. Slipher used planetary cameras to take photos of Mars, Venus, Jupiter, and Saturn.
In the 1960s, cartographers from the Air Force Aeronautical Chart and Information Center (ACIC) used the Clark to map the Moon for Apollo missions.
In 2014-2015, the Clark Telescope underwent an extensive restoration. Today, it is the jewel of the observatory's outreach program.