1576 — Pope Gregory XIII builds the Tower of the Winds to demonstrate the error in the Julian calendar.
1582 — The Gregorian calendar is published, relying on the scientific work of a commission Pope Gregory XIII established to study the stars.
1774 — Establishment of the Observatory of the Roman College.
1827-70 — The Vatican establishes the Observatory of the Capitol.
1789-1821 — The Vatican Observatory built in the Tower of the Winds.
1839-78 — The work of Jesuit Father Angelo Secchi of the Vatican Observatory creates the first classification of the stars according to their spectra, a system that, with modifications, is still used today.
1879 — The Italian government takes over the Vatican Observatory.
1888 — Pope Leo XIII refounds the Vatican Observatory.
1888-1928 — The Vatican Observatory participates with other world observatories in mapping the positions of 500,000 stars across the entire sky.
1930 — Pope Pius XI moves the Vatican Observatory to Castel Gandolfo, about 20 miles southeast of Rome, to avoid the brightening night sky of Rome. The library at Castel Gandolfo contains rare books of astronomy by Copernicus, Gallileo, Newton, Kepler, Brahe, Father Secchi and others.
1957 — Installation of wide-angle telescope in the Vatican Observatory.
1981 — Vatican Observatory Reseach Group established in Tucson, Ariz., with access to all the telescopes in the Tucson area.
1993 — Completion of the Vatican Advanced Technology Telescope, first optical-infrared telescope at the Mt. Graham International Observatory, the best astronomical site in the continental U.S., located near Tucson, Ariz.