The Signed Letter, Dated February 9, 1581:
The artifact presented here is interesting in that it was signed by Pope Gregory XIII and is dated February 9, 1581, prior to the enactment of the Gregorian calendar, which occurred on Thursday, October 4, 1582.
Historically, the Catholic Church has been a major sponsor of astronomy, not least due to the astronomical basis of the calendar by which holy days and Easter are determined.
The Church’s interest in astronomy began with purely practical concerns, when in the 16th century Pope Gregory XIII required astronomers to correct for the fact that the Julian calendar had fallen out of sync with the sky. Since the spring equinox was tied to the celebration of Easter, the Church considered that this steady movement in the date of the equinox was undesirable.
The resulting Gregorian calendar is the internationally accepted civil calendar used throughout the world today and is an important contribution of the Catholic Church to Western Civilization.
It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree, a papal bull, Inter Gravissimas, signed on 24 February 1582.
A Commentary Connected to Leap Years
Pope Gregory XIII’s Responsibility for Leap Years:
Something happens this month that happens only once every 1,460 days. I am, of course, referring to leap day, Feb. 29.
It’s easy to remember which years have 366 days because they coincide with presidential elections, although I am sure there is no connection between the two.
Leap year and leap day are not simply calendar oddities. They point to the influence of the Catholic Church on civilization. Until the 16th century, most of the world was using the Julian calendar, which had been established in 45 BC by the Roman Emperor Julius Caesar. The Julian calendar year was 365.25 days. Due to inaccuracies in this system, three days were gained every 400 years.
Over the centuries, people discovered the Julian calendar was becoming inaccurate simply by looking at the moon. By the 16th century, the lunar calendar was out of whack with the real moon by four days.
This had an effect on the church’s celebration of Easter, which, according to the Council of Nicaea in AD 325, had to be based on the vernal equinox. That was believed to be March 21, but due to the inaccuracies of the Julian calendar, the real lunar calendar started to affect Easter’s dating. Enter Pope Gregory XIII.
The science behind the formation of the calendar is much more complex than this, but suffice it to say it was Pope Gregory XIII (1572-1585) who, on Feb. 24, 1582, decreed in the papal bull “Inter gravissimas” that the calendar would be reformed later that year. By that time, the accumulated error over the centuries meant there were 10 days too many on the calendar. By the authority of that papal bull, the last day of the Julian calendar was Thursday, Oct. 4, 1582, while the first day of the Gregorian calendar — the very next day — was Friday, Oct. 15, 1582.
The exact Gregorian reform means that every year exactly divisible by four is a leap year, with the exception of the years that are divisible by 100. In those century years, only the ones that are exactly divisible by 400 are leap years. So the year 1900 was not a leap year, but the year 2000 was, because it was divisible by 400.
Although not everyone adopted the Gregorian reforms right away, it did not take long before the whole world went along with them. The last holdouts were Russia and Greece. They did not adopt the Gregorian calendar until the 20th century, and when they did, they had to drop 13 days from their calendar to do it. For some of their movable feasts, the Orthodox Church still observes the Julian calendar, but apart from them, almost all of civilization has a calendar named after the pope who promulgated it.
The calendar reforms of Pope Gregory XIII are tangibly seen in St. Peter’s Basilica. Several popes have large and impressive funerary monuments on the main floor of the basilica, and each monument has depicted on it the scene or episode for which that pope was most noted. On the actual sarcophagus of Gregory XIII is shown the scene of astronomers pointing out their discoveries to the pope, the discoveries, which were later named for him.
There is a very interesting aside to all this information on the calendar reforms instituted by the church. Most often, the Catholic Church celebrates saints’ feast days on the anniversary of the day the saint died because that it is the date on which they accomplished their mission of salvation. We celebrate birthdays; the church celebrates death days! Well, the Carmelite saint and doctor of the church Teresa of Avila was dying the night of Oct. 4, 1582. She died at the stroke of midnight (or very close to it), so her feast day is Oct. 15, the very next day, the first day of the Gregorian calendar.
Whenever you hear the term “Gregorian Calendar” being used, know that it is a point of influence of the Catholic Church and its popes. The church has had, and continues to have, influence over all aspects of Western Civilization, so much so that every calendar you own, whether it is on paper or on your iPad, is thanks in part to Pope Gregory XIII. —Father Richard Kunst