Pope Gregory XIII was an extraordinary innovator: he deserves the credit for the transformation of the School wanted by Saint Ignatius of Loyola in what will later be the Gregorian University, and especially for the calendar reform, by replacing the Julian calendar (which dates back to Juius Ceasar’s times) with what we now call “Gregorian” calendar.
It is the official calendar in the majority of the western world’s countries and has been developed by editing the Julian calendar. It is named after Pope Gregory XIII, who introduced it in 1582 with the Papal Bull <Inter Gravissimas> enacted in Villa Mondragone (in Monte Porzio Catone, Rome). The calendar revolves around the sun-based year, and therefore the seasons’ cycle. The year is composed by twelve months with a different length (from 28 to 31 days) for a total of 365 or 366 days: the 366 days year is called leap-year. Such repetition happens every four years, with some exceptions.
In order to reform the Julian calendar, Pope Gregory XIII nominated a specific commission chaired by Cristoforo Clavio, Jesuit professor of the Roman College. The Calabrian doctor Luigi Lilio, the Sicilian mathematician and astronomer Giuseppe Scala and the mathematician Ignazio Danti from Perugia gave a decisive contribute to the work. The measurements made by the astronomer Niccolò Copernico were used in order to adjust the Julian calendar and were published in 1543 (the year of his death) with the title < De Revolutionibus orbium coelestium libri sex> (“Six books regarding the circular movements of the celestial bodies”); he was able to calculate, with considerable accuracy, both the tropical year and the solar year.
It is a big and frescoed hall inside Palazzo Boncompagni. The extraordinary ‘Pope’s Hall’ was destined to papal auditions, for the occasions in which the Bolognese Pontiff came back in his hometown. The large reception hall on the ground floor, which has exceptional acoustic characteristics, is adorned with a beautiful and rare Serena stone chimney, probably crafted on a Pellegrino Tibaldi’s drawing, who later painted the frescos of the ceiling and the space above the chimney with his pupils, during the second half of the 1500s.