Universitäts-Sternwarte Wien (Vienna Observatory) is an astronomical observatory in Vienna, Austria. It is part of the University of Vienna. The first observatory was built in 1753-1754 on the roof of one of the university buildings. A new observatory was built between 1874 and 1879, and was finally inaugurated by Emperor Franz Joseph I of Austria in 1883. The main dome houses a refractor with a diameter of 68 centimetres (27 in) and a focal length of 10.5 metres (34 ft) built by the Grubb Telescope Company. At that time, it was the World's largest refracting telescope.