Today is the “Bissextile” day
“The year hath twelve months, comprising fifty-two weeks, and one day : indeed, it has three hundred and sixty-five days, and nearly six hours ; for in such an interval of time the sun traverses the zodiac. However, in the course of four years, four times six hours constitutes an extra day ; hence that year is called intercalary, bissextus, or bissextile.”
– De anno et ejus partibus (my working translation)
Well folks, this is such a year, and today is the day, liturgically speaking.
“In a bissextile year, the month of February is 29 days long, and the feast of St. Matthias [note: usually on the 24th] is celebrated on the 25th day of February, and the feast of St. Gabriel of Our Lady of Sorrows [note: usually on the 27th] on the 28th day of February, and the Sixth Kalends are said twice, that is, on the 24th day and on the 25th day ; and the dominical letter, which was taken up in the month of January, is changed into the preceding one : as for example, if in January the dominical letter was A, it is changed into the preceding one, which is g, etc., and the letter f serves twice, on the 24th and on the 25th.”
– Calendarium romanum (my working translation)
In the Roman method of reckoning, days are counted backwards from certain set points in each month: the Kalends, the Nones, and the Ides.
Since the Kalends are always the first day of the month, the first day of March is called “the Kalends of March”;
The last day of February is called “the day before the Kalends of March”;
The second last day of February is called “the Third Kalends of March”;
The third last day of February is called “the Fourth Kalends of March”;
And so on.
(By the way, this numbering system is an example of what is called “inclusive counting”.)
Now, counting backwards like this, the “Sixth Kalends of March” is February 24th in most years, but in leap-year when you add an extra day to the end of the month, the Sixth Kalends suddenly becomes February 25th.
Since we are talking about the Roman calendar, it should not surprise us to find that the feast of St. Matthias is affixed to the Roman-style date, the Sixth Kalends, and not to February 24th.
This goes for the other (later) feast that occurs near the end of the month, St. Gabriel of Our Lady of Sorrows, as well.
So where’s the leap-day?
As it happens, when an extra day was to be inserted into the Roman calendar, their method of doing this was to have two days which were both “the Sixth Kalends of March”; these correspond to our February 24th and 25th.
Since the feast of St. Matthias is to be celebrated on the 25th, we may therefore deduce that the intercalary (that is, “inserted”) day, the bissextile (that is, “twice-sixth”) day, is in fact February 24th.
In fact, in an English version of the Roman Martyrology which I have, the direction in this regard is:
But in Leap Year on February 24 is read only:
The commemoration of many holy martyrs and confessors and holy virgins. R. Thanks be to God.
So, there you have it.
Happy Bissextile day!