It was used in the 1930's to help determine Pluto's orbit and for over 40 years was used to make Kodachrome photographs of the planets and other celestial formations. It was decommisioned in the late 1990's and put on outside display in 2001, without the optics. The telescope was replaced by another 42 inch unit that uses low expansion glass in 1969 and is in a more remote location outside of Flaggstaff.