The Lowdown on Leap Years

Today is February 29—that extra day in February that turns every fourth year into a leap year.

Why do we have a leap day? Well, that question comes back to why we have a year at all. The seasons, the day, and the year are the primordial units of time, mentioned as part of the structure of creation in Genesis 1:14.

The Genesis writer doesn’t reflect on how those units of time come about and recur. He takes their repetition as a divine gift.

But our faith is not blind, ignoring reason. Not only did man experience the recurrence of those fixed times, but he eventually also asked why they recurred.

That led to man looking at the heavens, “the work of [God’s] hands” (Ps. 8:3), “declaring the glory of God” (19:1-2) not only in their magnificence, but also in their workings and order. The day was not just the daily commute of Helios across the sky, nor the seasons just some eternal cycle . . . because the year saw those “cycles” repeat themselves through advancing time.

That idea of time’s advance, not just its eternal recycling, is necessary to any concept of history. Without it, “all the world’s a stage” on which all men and women are reincarnated players, or . . . well, “life is hard, and then you die.” The Christian (and Jewish) concept of time rules out re-incarnation (an eternal return). But it does make possible the Incarnation—not just of Christ, but of every man, given freedom and a gift of time, to create (or fail to create) a unique work of art called love.

Eventually, those Jews and Christians also got to the how of the days, seasons, and years. The day is the product of rotation. The year is the product of revolution of the earth around the sun, while the seasons are how a particular piece of geography stands in relation on its earthly axis to the sun. The earth’s revolution from point A back to point A was taken as 365 and one quarter days, so, voilà: a quarter of a day every year added up to an extra day every four.

Alas, the earth’s revolution is not quite 365.25 days—i.e., 365 days and 6 hours. It’s 365 days, 5 hours, 48 minutes, and 46 seconds—a little more than 11 minutes short of a quarter-day. That may not seem like much to man, whose life is “seventy years, or eighty for those who are strong” (Ps. 90:10), but over those seventy years, the calendar outruns the sun by about twelve hours—half a day.

Again, that might not seem like much. Julius Caesar started leap years in 45 B.C. By the time we get to Pope Gregory XIII, of Gregorian Calendar of 1582 fame, those 11 minutes per year had accumulated to 12.5 days. That meant the sun and the calendar were out of alignment by nearly two weeks, resulting in the sky saying “spring’ but the calendar “winter,” both facts relevant for fixing Easter. If you want proof of the problem, consider the dissonance between feasts like Easter and Christmas in the Catholic Church and those Orthodox churches (e.g., Russia’s) still clinging to the Julian Calendar, now about fifteen days out of solar alignment.

Pope Gregory XIII applied faith and reason through a minor modification to the leap year rule. A leap year is any year evenly divisible by four. Gregory added a corollary: no centennial year can be a leap year unless it’s also divisible by 400. So 2000 was a leap year; 2100 will not be. That little trick will keep calendar and sun aligned for several thousand more years.

So faith, reason, and the calendar have a lot to do with leap year. But so does calendar “reform.”

As noted above, the day, seasons, and years are experienced as primordial units of time, connected to the sun, the “greater light to rule the day” (Gen. 1:16). The “week” is a bit less obvious. It more or less approximates half-phases of the moon, “the lesser light to govern the night.” But the week acquired its fixed dimensions in the Genesis 1 creation account as the unit of time marked by the recurrent “Lord’s Day” every seventh.

The year—365 or 366 days—is not evenly divisible by seven, one consequence of which is that dates are moveable in relation to days. February 28 was a Wednesday this year; it’ll be a Friday next year. That means calendars need to be changed annually. Afficionados of efficiency don’t like that.

There have been proposals to create something called a “perpetual calendar,” where particular dates would always fall on the same day. One version would start every quarter of the year (e.g., January, April, July, and October 1) on a Sunday, each quarter having ninety-one days. That gives 364 days. To keep day and date aligned, the 365th (and, every four years, 366th day) would be some sort of “universal” dates, days independent of the week. They would be dates, but they would not correspond to any week-days.

The “Appendix” to Vatican II’s Constitution on the Sacred Liturgy (Sacrosanctum Concilium) declares a willingness to accept a perpetual calendar, provided two conditions are honored: retention of the seven-day week and no dates outside the seven-day week.

The history of the calendar has been marked by conscious attempts to eliminate the week, primarily out of animus toward its religious origins. That was the driving force in both the French Revolutionaries’ and Bolsheviks’ calendars. The question today is whether Christians, for whom the distinctiveness of the “Lord’s Day” has withered, can withstand any organized push against creating a more “efficient” calendar not arranged by “non-inclusive” vestiges of once-dominant religions. In that regard, the protection of the seven weekdays of a seven-day week is important. It’s why we should thank God it’s Thursday . . . February 29!