File:Vatican Observatory, Castel Gandolfo.jpg

English: Two domes of the Vatican observatory, located in the pontifical gardens of Villa Barberini.

The smaller dome (right) was built in 1941, when the "Carte du Ciel" telescope, that was installed in the Vatican in 1891, was moved to Castel Gandolfo due to the increasing light pollution in Rome. The Vatican Observatory was one of about 20 obseravtories around the world that cooperated in the <a href="https://en.wikipedia.org/wiki/Carte_du_Ciel" rel="nofollow">"Carte du Ciel" project</a>, with the goal of mapping the whole sky on photographic plates that were taken trough identical telescopes. These "Carte du Ciel" telescopes consist of a 13" photographic lens with a focal length of 343 cm (resulting in an image scale of 1'/mm) and 8" refractor with 360 cm focal length, used as guide scope, on a common English equatorial mount.

The larger dome was built in 1954 for a 65/98/240 cm Schmidt telescope that arrived in Castel Gandolfo in 1957. Using 20x20cm² glass plates, photos taken with this Schmidt telescope covered an area of 5°x5° in the sky, more than six times larger than the field of the "Carte du Ciel" astrograph. For spectrography, objectiv prisms could be mounted at the aperture of the telescope, which then recorded low-resolution spectre of all objects in the field.