In its historical roots the Vatican Observatory is one of the oldest astronomical institutions in the world. The first foreshadowing of the Observatory can be traced to Pope Gregory XIII and the constitution of a committee to study the scientific data and implications involved in the reform of the Julian calendar in use since 45 B.C. That calendar contained a tiny error in determining the length of the year, and by the late 1500s the error had grown large enough to make timing of Church holy days out of sync with their respective seasons. The committee working on the project included Fr. Christoph Clavius, a Jesuit mathematician from the Roman College, who expounded and explained the reform of the calendar.


From that time, the Papacy has manifested an interest in and support for astronomical research. In fact, several pontifical observatories were established in Rome, including the Observatory of the Roman College, the Observatory on the Capitoline Hill and the Specola Vaticana (or Vatican Observatory). These early traditions of observational astronomy reached their climax in the mid-nineteenth century with the research of the Jesuit, Fr. Angelo Secchi, at the Roman College. The most prolific of those who first classified stars according to their spectra, Fr. Secchi is often referred to as the "Father of Modern Astrophysics" and his technique remains important in modern research.


Following the unification of Italy in 1870, the pontifical observatories became state property.  Despite this setback, the Vatican continued its support of astronomy, and in an effort to counteract the accusations that there was a conflict between the Church and science, Pope Leo XIII formally re-founded the Specola Vaticana (Vatican Observatory) in 1891.


From a hillside behind St. Peter's Basilica, Vatican astronomers studied the heavens, taking part in an international program to map the whole sky.  By the 1930s, however, the city's lights had begun to blot out the fainter stars, and in 1935 Pope Pius XI moved the Observatory to the papal summer residence at Castel Gandolfo, a town in the Alban Hills about 25 kilometers outside Rome.


Urban light pollution once again caught up with the astronomers at Castel Gandolfo, and in 1980 they established a new division of the Observatory in Tucson, Arizona, an internationally recognized center for astronomy. This location in the United States is called the Vatican Observatory Research Group (VORG) and is hosted by the University of Arizona's Steward Observatory.


New technology developed by Roger Angel and colleagues at the Steward Observatory offered significant promise for developing a more powerful telescope at considerable cost savings. Collaborating with the Steward Observatory, the Vatican Observatory built the Vatican Advanced Technology Telescope (VATT) on Mt. Graham in southeastern Arizona. Funding for the project was only possible with the generosity of private, philanthropic support. Hence, in 1987 the Vatican Observatory Foundation was established.


Dedicated in 1993, the VATT utilizes some of the most advanced and innovative optics, electronics and mechanics available — once again positioning the Vatican at the forefront of astronomy.