Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965. In 2011, the Observatory was named one of "The World's 100 Most Important Places" by Time magazine. It was at the Lowell Observatory that the dwarf planet Pluto was discovered in 1930 by Clyde Tombaugh. Lowell is home to a 24-inch Clark Refracting Telescope, built in 1896, which is still in use today for public observing. Lowell sees over 150,000 annual visitors and is active in exoplanet and minor planet research.