On July 23, 1896, the first specifically designed telescope, the 24-inch Clark Telescope, was used to view the dark skies over Arizona. The Lowell Observtory was built by Percival Lowell in 1894. Percival was an astronomer and mathematician who was in search of clearer skies in order to observe the planets and stars. With the help of AE Douglass, they found this small corner of the world. In 1930, with the help of the Clark Telescope, Clyde Tombaugh discovered a ninth planet, Pluto, finishing the work that Percival started some 25 years earlier.
Today the Lowell Observatory is a big tourist attraction. Is also houses the Discovery Channel Telescope. The observatory still does plenty of research and has pictures of the Hale-Bopp Comet.
It's open all year, at different times during the different seasons. Entrance is $5 for adults.