Kevin's Watch

Feb. 29, 45 B.C.: Julius Caesar Takes the Leap
By Randy Alfred 02.29.08 | 12:00 AM


Great Caesar's ghost! Julius Caesar fixed the calendar for centuries to come.

45 B.C.: Roman dictator-for-life Julius Caesar, alarmed that the calendar is growing out of whack with the seasons, adds an extra day to the month of February every four years.

Caesar was reforming a calendar based on 364 days, with an occasional extra leap month. But the Roman religious officials in charge of minding the calendar had been asleep at the switch, chronologically speaking. Caesar consulted with Egypt's top astronomers, who told him the year was 365¼ days long. While he was making the fix, Julius also decided to give his name to the month of July.

Although Caesar decreed the new calendar in 46 B.C., that year had 15 months to make up for the accumulated discrepancy. The first add-a-day leap year was 45 B.C.

The new Julian leap day wasn't added at the end of February originally, but on the day preceding the 6th of the calends of March. The Romans didn't count the days of the months from 1 on up, but used an idiosyncratic system of calends, nons and ides -- and we all know what happened to ol' J.C. on the ides of March, 44 B.C.

The 6th of calends of March was the sixth day before the first day of March, and, since even non-leap Februarys had 29 days back then, the 6th of calends of March was akin to Feb. 25. So Leap Day would have been Feb. 24 by modern nomenclature, more or less.

Though the Julian Calendar was more accurate than what preceded it, it wasn't really as accurate as it needed to be. That's because an Earth year is about 11 minutes short of 365¼ days: It's 365 days, 5 hours, 48 minutes, 46 seconds. This was known, more or less, since the second century A.D., but by 1582, the calendar was 10 days out of whack, and Easter was falling too late in the real spring. So Pope Gregory XIII tweaked the Julian Calendar by subtracting three leap years in every 400 (years ending in 00, unless they are divisible by 400).

The Gregorian Calendar became law in the Catholic countries of Europe (and their colonies) immediately, but was resisted in Protestant and Eastern Orthodox lands. As a result, the Julian Calendar held on for quite some time: 1752 in Britain and its colonies, for instance, and right through 1918 in Russia.

That's why the old Soviet Union used to celebrate its (Julian) October Revolution of 1917 each year in (Gregorian) November, and one of the reasons that Orthodox Christmas and Easter fall on different dates from their observance by Western churches.

It's all arbitrary. The United States celebrates Washington's Birthday on the third Monday in February, even though George observed it on Feb. 22 after 1752, even though he was born on Feb. 11 in the Julian (or Old Style) calendar. So that's why Wired.com is marking the anniversary of the first leap day on our current leap day.