The Vatican Observatory emerged from the Church’s long-standing tradition of interest in astronomy, linked to the Gregorian reform of the calendar and to the scientific activities of the Jesuits at the Roman College. After the loss of the Roman College Observatory in 1879, Pope Leo XIII promoted the establishment of a new observatory in 1888, entrusting its creation to the Jesuit Fr. Francesco Denza. The scientific instruments were placed in the Tower of the Winds, where Denza organized a center that quickly gained international recognition.

A fundamental moment was the participation in the international Carte du Ciel project, launched in Paris in 1887. The Vatican Observatory contributed to the systematic photography and measurement of the stars, also thanks to the large astrograph installed in 1891 on the Leonine Tower. After Denza’s death, Fr. Giuseppe Lais continued the photographic work for many years, producing hundreds of photographic plates and contributing to the cataloguing of the stars.

In 1906, the directorship passed to Fr. Johan Hagen, who reorganized the observatory and strengthened its facilities and instruments. Under his direction, an important Astrographic Catalogue, containing 481,215 stars, was completed, and studies were conducted on the rotation of the Earth.

As light pollution in Rome progressively increased, under Pope Pius XI the Observatory was transferred to Castel Gandolfo between 1932 and 1935. New telescopes were installed there, and an important astrophysical and spectroscopic laboratory was established under the direction of Fr. Alois Gatterer, who produced important spectral atlases and founded the journal Spectrochimica Acta in 1939.

The Second World War temporarily interrupted the Observatory’s activities: Castel Gandolfo became a refuge for thousands of displaced people, and the Vatican Observatory community had to move temporarily to Rome. After the war, research resumed, and in 1958 the Vatican’s contribution to the Carte du Ciel was officially completed.

The Observatory then broadened its research interests, focusing on the study of the Milky Way and variable stars. Fr. Walter Miller identified approximately 500 new variable stars, while Fr. Daniel O’Connell and Br. Karl Treuschstudied the phenomenon known as the green flash. In 1957, the Schmidt telescope was also installed and was used for important spectroscopic research.

In the 1960s, the Observatory entered the age of computing, establishing a Computing Center in 1965 for the processing of astronomical data. In the 1970s, however, Castel Gandolfo also became too bright for the needs of astronomical research. Under the direction of Fr. George Coyne, the Observatory therefore began a collaboration with the University of Arizona and, from 1980 onward, used the facilities of the Steward Observatory in Tucson.

This collaboration led to the construction of the Vatican Advanced Technology Telescope (VATT) on Mount Graham, at an altitude of approximately 3,200 meters. The project, also supported by the Vatican Observatory Foundation, marked a new phase in the history of the Observatory, characterized by the use of advanced optical technologies and close collaboration with the international astronomical research community.