The Vatican Observatory traces its 1582 origins to Gregory’s pontificate and the Gregorian calendar reform. Located at the papal summer residence in Castel Gandolfo in the hills south of Rome ...

In 1582, Pope Gregory XIII issued a papal bull that officially ended the use of the Julian calendar, introducing in its place what we now know as the Gregorian calendar. This reform marked the ...

That conflict was almost the inevitable outcome of a feature of an intimately related phenomenon known as the Gregorian Reform, which had originated earlier in the mid-11th century with a small ...

FILE - The sun sets behind the dome of St. Peter's Basilica, in Rome, on Feb. 20, 2023. Pope Gregory XIII, the 16th century pontiff responsible for what is today known as the Gregorian calendar ...