This column ran in The Tablet for the new year's issue of 2008, when Easter occurred remarkably early, on March 23. It was relatively early in 2016, on March 27th, when we ran it here. This year, it's about as late as it can be! Early or late, the explanation is the same... and so probably worth running again.
Why is Ash Wednesday so late this year?
Contrary to popular conception, the Vatican Observatory doesn’t set the date of Easter. (We don’t cast horoscopes for the Pope, or evangelize UFOs, either.) But since Pope Gregory’s reform of the calendar in 1582 marked the beginning of the Vatican’s support for astronomy, we have a historical connection.
Our calendars have always been marked by a confusion of days, planets, and gods. Even today, our week begins with the Sun’s day, followed by the Moon’s day and ending with Saturn’s Day. The month (think, “moonth”) was originally based on the 29.5 day period of the Moon, while the year is fixed by the Sun’s apparent motion through the zodiac. If your culture is centered on animals — fishing, hunting, caring for flocks at night — moonlight and tides will control your life and your calendar will follow the Moon. If you grow crops, then seasons are more important, and a solar calendar makes more sense.
The Jewish calendar, including such festivals as Passover, is lunar; the civil calendar of Rome, set by Julius Caesar, is solar. The Church’s calendar is a holy marriage of both. Thus, most saints' days are fixed into the yearly calendar, like Christmas; but Easter was set by the Council of Nicaea as the first Sunday after Passover.
By medieval times, our astronomy had advanced to the point where it it should have been possible to calculate when those lunar holy days would occur. But in practice, such calculations turned out to be surprisingly difficult.
By the 16th century, with Christianity spreading across the globe, it became all the more urgent to find a simple, reliable way of letting everyone know well ahead of time when Easter and its associated feasts were to be celebrated. (In addition, Caesar’s trick of leap years every fourth year was proving to be not quite precise enough; after 1500 years, the first day of spring had slid by 10 days from its canonical position of March 21.)
Pope Gregory’s calendar committee, commissioned by the Council of Trent, settled on a simple and elegant solution first proposed by Aloysius Lillius. Instead of trying to determine with perfect accuracy the Moon’s position and the first day of spring, they devised a formula which closely, if not exactly, follows the “first Sunday after Passover” rubric. (In fact, they differ roughly 5% of the time.) The earliest that Easter can fall is March 22; this occurs roughly once every two centuries. A March 23 date, such as we had in 2008, is a once-a-century event; the next one is in 2160. Meanwhile, the latest Easter can occur is April 25, which will next happen in 2038; on that day, Ash Wednesday is on March 10.
What’s more significant, however, is the underlying principle behind this arbitrary formula. The Sabbath was made for man, not man for the Sabbath: our religious feasts are not controlled by the Moon. And so future colonists on Mars or beyond can set Easter for whatever date best suits them. That may turn out to be a very useful principle, once it comes time to evangelize those UFOs!