C T Hall’s Weblog

(or Intercalary Day if you prefer.)

Often,* one hears that the real leap day is 24 February instead of 29 February. Of course one thinks, ‘But there’s a 24 Feb every year, this doesn’t make sense.’ Indeed, I concur. However, I thought it might be interesting to shed light on why 24 February was considered the intercalary day.

This started back in ancient Rome, where months were not counted as they are now. The Romans had three important days each month, the calends (or kalends) (the first of the month), the nones (the fifth or seventh of the month [the ninth inclusive day before the ides]), and the ides (the thirteenth or fifteenth). The Romans (inclusively) counted down to each day, e.g., today would be the Second of the Calends of March, tomorrow the Calends of March, 21 April the Eleventh of the Calends of May, and 4 August the Second of the Nones of August.

Before Julius Caesar, the Romans used a lunisolar calendar (a calendar that tracked lunar months as well as the solar year). In order to keep the months lined up with the years every so often the ancient romans inserted a month at the end of the year before the last five days of February. Julius Caesar reformed the calendar to a solar calendar. He distributed the extra days of the intercalary month amongst the other months of the year. For the leap year, he inserted an intercalary day after the festival of Terminus (the god of boundaries). Terminalia was on 23 February or the Seventh of the Calends of March. Rather than renumber the days, the date following Terminalia was doubled so that the Seventh of the Calends of March was followed by the Second Sixth† of the Calends of March‡ which was followed by the Sixth otCoM. For a while the Roman church (until the 1970’s) had celebrated saints’ festivals on this pattern (pushing back feasts one day on 24-28 Feb).

And now you know the origin of 24 February as Bissextile day, and the irrelevant trivia section of your mind has expanded.

Homer: How is education supposed to make me feel smarter? Besides, every time I learn something new, it pushes some old stuff out of my brain. Remember when I took that home winemaking course, and I forgot how to drive?
Marge: That’s because you were drunk!
Homer: And how!

Footnotes:
* Okay, maybe only if you’re into recondite trivia.
† Much like Fifth Third Bank.
‡ Known now as Bissextile Day.