[2] The Church has had a long-standing interest in astronomy, due to the astronomical basis of the calendar by which holy days and Easter are determined.

For instance, the Gregorian Calendar, promulgated in 1582 by Pope Gregory XIII, was developed by Aloysius Lilius and later modified by Christoph Clavius at the Collegio Romano from astronomical data.

Father Angelo Secchi SJ relocated the College Observatory to the top of Sant'Ignazio di Loyola a Campo Marzio (Church of St. Ignatius in Rome).

In the late nineteenth-century the Vatican Observatory was part of a group of top astronomy institutions from around the world which worked together to create a photographic "Celestial Map" ("Carte du Ciel") and an "astrographic" catalog pinpointing the stars' positions.

In the early twentieth-century Father John Hagen took over the project and recruited a group of nuns from the Sisters of the Holy Child Mary to work on the necessary recording and calculations.

[6] In 1993, VORG completed construction of the 1.8 metres (71 in) Vatican Advanced Technology Telescope, which is at Mount Graham near Safford, Arizona.

In early 2008, the Vatican announced that the Observatory would be relocated to a former convent a mile away from the castle as part of a general reconstruction of the Papal residence.