The origins of leap year go back a few thousand years

When people sometimes tell me that I look good for my age — and is that really a compliment? — they probably don’t realize that I’m still a teenager. Forget the wrinkles and gray hair and focus on the fact that I have a birthday only once every four years — Feb. 29 to be exact.

And that, as I like to say, is my ace in the hole.

To get you ready for the extra day this year, let me tell you how the calendar got to be what we think it is. Keep in mind that its history, or what we know of it, rests on myth, religion and whim. It’s almost as complex and incomprehensible as our Internal Revenue Code and at least as devious.

And to add to the mix, there’s not just one but many calendars.

Perhaps the oldest existing calendar is the Chinese, going back a few millennia. But the Chinese don’t really number their years, counting instead in 60-year cycles, divided into five 12-year cycles named after different animals. Right now, as you all should know, it’s the Year of the Dragon, a lucky time to be born in, so look forward to a spike in the Chinese birth rate.

The Chinese calendar is a lunar one, as is the Hebrew calendar, now marking the year 5772. That year is counted from the creation of the earth, although science suggests that such a calculation may be off by a few billion years.

What we’re most familiar with is, of course, our Western calendar, accepted today by most people worldwide and calculated on how long it takes for the earth to travel around the sun. Galileo got into trouble for this theory about 400 years ago, but I digress.

The ancient Egyptians and Greeks followed the sun with a 10-month calendar, each month from 20 to 35 days in length. When Rome was founded by those lovable twins Romulus and Remus, two more months were added, with the year starting on the first of March.

By the time of Julius Caesar, however, things were seriously out of whack. So the year we refer to as 46 B.C. was adjusted to a length of 445 days, called by the Romans, not surprisingly, the Year of Confusion. Caesar, being Caesar, began the year with January, changed the former Quintilis to what we call July, and divided the months into 30 and 31 days — except for February which had 29 days and 30 every fourth year.

When Augustus took power, he also opted for naming rights, turning Sextilis into August and taking a day from poor February so that his month would be as long as July.

This was the Julian calendar — based on the earth’s travel around the sun in 365 1/4 days. It was pretty accurate but a tad long — off by a mere 11 minutes and 14 seconds. Over the centuries, those few minutes added up, so in 1582 a correction was made under Pope Gregory XIII: 11 days were dropped from the calendar, so Oct. 4 became Oct. 15.

And century years were no longer to have that extra February day, unless divided by 400. For instance, 2000 was a leap year, but not 1900. This Gregorian calendar is almost completely accurate — the difference between the solar and calendar years is now only 26.3 seconds.

Got it?

But then there’s the question as to how we number the years. Around the year 530, a monk named Dionysius Exiguus, known to his buddies as Denis the Little, was put to the task of calculating the exact date of Easter.

He had a lot of time on his hands, no Angry Birds or texting to distract him, so he was able to come up with a formula that counted back to the birth of Jesus Christ, a historically unknown date, but nonetheless such research was later popularized in the eighth century by St. Bede the Venerable.

But relying on biblical references, scholars and theologians now agree that Denis missed the date of the Nativity by four to seven years. He also counted from A.D. 1, not Year Zero, so our present millennium began with 2001, not 2000, for those of you who remember all the Y2K fuss.

Which brings us to the Mayan calendar and the predicted end of the world Dec. 21. Not to worry, since time and dates are just a pleasant fiction, invented by humans to give us some structure and just as real as a television reality show.

Anyway, all I know is that come Feb. 29, I’m throwing myself a party.