Meridian Circle Telescope

Meridian telescopes like this one were used in the 19th century to determine sidereal time by observing the precise moment when stars of known location exactly crossed the meridian. This telescope was made at the Vienna Polytechnic in 1862 and donated in 1888 to the Vatican from the estate of Marquis of Montecuccoli, who had operated a private observatory at Modena. It has an aperture of 7.75 cm, and a focal length of 95 cm. It was installed in Castel Gandolfo when the observatory moved, but in practice it was never used there.