I saw this post in Intentional Disciples on the Gregorian Calendar reform. Resolving the disconnect between the Julian Calendar and the astronomical reality was one of the fruits of the Council of Trent. I suppose we could see how many Catholic progressives really abjure Trent by asking them what today’s date is.
The motivation of the Catholic Church in adjusting the calendar was to celebrate Easter at the time it thought the First Council of Nicaea had agreed upon in 325. Although a canon of the council implies that all churches used the same Easter, they did not.
By the tenth century all churches (except for some on the eastern border of the Byzantine Empire) had adopted the Alexandrian Easter, which still placed the vernal equinox on 21 March, although Bede had already noted its drift in 725—it had drifted even further by the sixteenth century.
Worse, the reckoned Moon that was used to compute Easter was fixed to the Julian year by a 19 year cycle. However, that approximation built up an error of one day every 310 years, so by the sixteenth century the lunar calendar was out of phase with the real Moon by four days.
The Council of Trent approved a plan in 1563 for correcting the calendrical errors, requiring that the date of the vernal equinox be restored to that which it held at the time of the First Council of Nicaea in 325 and that an alteration to the calendar be designed to prevent future drift. This would allow for a more consistent and accurate scheduling of the feast of Easter.
Thanks to this reform, we drop three leap-days (29 February) every three centuries. Pope Gregory’s astronomers recommended reworking century leap years, leaving multiples of 400 alone (1600AD, 2000AD, 2400AD, etc.) but dropping the 29th of February in other century years, our next being 2100AD.
I noticed that Alaska had two consecutive Fridays when Seward acquired it from the Tsar:
In Alaska, the change took place when Friday, October 6, 1867 was followed again by Friday, October 18 after the US purchase of Alaska from Russia, which was still on the Julian calendar. Instead of 12 days, only 11 were skipped, and the day of the week was repeated on successive days, because the International Date Line was shifted from Alaska’s eastern to western boundary along with the change to the Gregorian calendar.
The whole idea of a Perpetual Calendar with non-week holidays is troublesome to many believers, so I wonder how TGIF2 passed in Alaska?
Some curious trivia:
Saint Teresa of Ávila died on the night from October 4 to October 15, 1582, that is, exactly when Spain and the Catholic world switched to the Gregorian calendar.
Shakespeare and Cervantes died on exactly the same date, April 23, 1616. However, since England had not adopted the Gregorian calendar by that time, they did not die the same day. In their honor, UNESCO declared it International Day of the Book.
As human beings settle Mars, it will be interesting to see how the gradual split of Earth days from sols is handled by settlers there. The observance of Sabbath/Sunday will have more of an effect than the fixing of Easter, due to the 39.5 minutes longer it takes Mars to rotate on its axis. Every thirty-six-and-a-half days, the Martian sol and Earth day realign. But if Mars keeps a seven-day week, when the Red Planet settlers reach their sixth Sunday, it will be mostly Monday and a little bit of Tuesday on the Earth.
I was surprised to find numerous published attempts at creating a Mars calendar for explorers who are probably two to four decades (at least) from getting there. One uses 24 months. Another keeps the Terran 12-month system, but with length variations covering 49 to 70 days. (“Fifty-six days hath Septmeber …”)
Somehow I suspect a Church council won’t be behind the new calendars as these new worlds are settled.