From the Tablet: Why is Easter So Early This Year?
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Easter occurs relatively early in 2016, on March 27th. But in 2008, it occurred even earlier, on the 23rd. The column ran in The Tablet for the new year's issue of 2008.

This page from Fr. Christopher Clavius' 1603 book explaining the reform of the calendar lists his calculations moveable feasts during our epoch

This page from Fr. Christopher Clavius' 1603 book explaining the reform of the calendar lists his calculations moveable feasts during our epoch. Note the typo for 2014 -- Easter was late that year and so Ash Wednesday should actually have been 5.Mar not 5.Feb!

Why is Easter so early 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.]

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!

Br. Guy Consolmagno

About Br. Guy Consolmagno

Brother Guy Consolmagno SJ is Director of the the Vatican Observatory and President of the Vatican Observatory Foundation. A native of Detroit, Michigan, he earned undergraduate and masters' degrees from MIT, and a Ph. D. in Planetary Science from the University of Arizona; he was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989.

At the Vatican Observatory since 1993, his research explores connections between meteorites, asteroids, and the evolution of small solar system bodies, observing Kuiper Belt comets with the Vatican's 1.8 meter telescope in Arizona, and applying his measure of meteorite physical properties to understanding asteroid origins and structure. Along with more than 200 scientific publications, he is the author of a number of popular books including Turn Left at Orion (with Dan Davis), and most recently Would You Baptize an Extraterrestial? (with Father Paul Mueller, SJ). He also has hosted science programs for BBC Radio 4, been interviewed in numerous documentary films, appeared on The Colbert Report, and for more than ten years he has written a monthly science column for the British Catholic magazine, The Tablet.

Dr. Consolmagno's work has taken him to every continent on Earth; for example, in 1996 he spent six weeks collecting meteorites with a NASA team on the blue ice regions of East Antarctica. He has served on the governing boards of the Meteoritical Society; the American Astronomical Society Division for Planetary Sciences (of which he was chair in 2006-2007); and IAU Commission 16 (Planets and Satellites). In 2000, the small bodies nomenclature committee of the IAU named an asteroid, 4597 Consolmagno, in recognition of his work. In 2014 he received the Carl Sagan Medal from the American Astronomical Society Division for Planetary Sciences for excellence in public communication in planetary sciences.

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