Easter: why it never falls on the same date two years running.

For centuries, scholars and historians have applied complex calculations to establish the day and year of Jesus death, to estimate his age and unite the Eastern and Western traditions of Christian belief.

The date to celebrate Jesus’ death and resurrection has been a point of division between the major strands of Christian tradition for centuries. Why can we still not agree?

But with historical sources scarce, verification of the exact date and even the precise year of that first Good Friday and Easter Sunday morning is somewhere between difficult and impossible to fix in historical time.

Biblical, historical and scientific sources

On the biblical information alone, Jesus lived during the reign of Roman Emperor Tiberius and during the period of the second Temple in Jerusalem. From the writings of Josephus and Tacitus, and the differing Gospel inferences on the years of Jesus ministry, scholars estimate his birth as between 4 and 6 BC, and his death 30 to 33 years later.

Verifying the precise years of Jesus ministry is further completed by calculations based on the moon, stars and movements of the planets. Biblical accounts report observations of new ‘stars’ at the birth of Jesus and ‘eclipses’ around the time of the crucifixion – scientific events would help fix Jesus in historical time.

Linking the crucifixion to the Passover

Biblically, the crucifixion and resurrection of Jesus is tied to the Jewish Feast of the Passover, beginning annually on the evening before the Sabbath of the 15th day of the Jewish month of Nisan. So the first ever Christian observance of Jesus death might have been the 14th day of Nisan the following year.

Since the beginning of ‘Christian Easter’ celebrations, there were disputes over the exact date of to observe. Tied to the Jewish lunar month of Nisan, but following a solar calendar, ‘Easter Day’ would fall on a different day of the week each year – just like Christmas Day, which is tied to 25 December.

Beginning to celebrating a ‘Christian Easter’

Whenever Christians did start to formally commemorate the death and resurrection of Jesus, the annual observation was commonplace by the second century AD. However, to call this celebration Easter would be incorrect, and this name reflects a later ‘conversion’ of pagan symbols of spring, new life and fertility customs into Christian symbolism and practice. But it’s a convenient name to use.

Churches developing into the Eastern tradition wanted Easter to remain tied to the Jewish Passover every year on the 14th of Nisan, and this was the date of Jesus Crucifixion. Churches beginning to distinguish themselves in a recognisably Western tradition insisted that Easter Day should always be a Sunday regardless of the date.

Settling Eastern and Western differences

At the Council of Nicaea in 325AD, under the First Christian Roman Emperor, Constantine, The date of Easter Day was fixed as the Sunday following the first full moon after the vernal (spring) equinox. That should have been it, but fixing the date of the equinox – when day and night are exactly the same length was still a problem.

Christian astronomers based in Alexandria, Egypt calculated that March 21 was the most likely date of the spring equinox. However, not every church agreed with the determining point of the calculations. Eastern Churches preferred to use the date of the equinox as calculated from its observation not in Alexandria in Jerusalem, site of Jesus crucifixion.

Julius Caesar, Pope Gregory and the moon

Further complications around harmonising Eastern and Western traditions arise with the Western adherence to the Gregorian calendar, and the Eastern Church calendar still based on the older Julian calendar. Each calendar deals slightly differently with the incomplete number of days it takes the Earth to complete and orbit of the sun.

In the 16th century most of Europe and Churches in the Roman Christian tradition moved from the older and less accurate calendar of Julius Caesar to Pope Gregory XIII’s ‘Gregorian’ version. The Eastern Churches stayed with the Julian.

Eastern and Western Easters today

The combination of different calendars and different ways of measuring the spring equinox means that this year - 2012, Western Christians will celebrate Jesus’ resurrection on Sunday 8 April but most Eastern and Orthodox faith traditions won’t be rejoicing in this way for another week. Yet last year in 2011, Western and Eastern celebrations occurred on the same 24 April.

Today, fixing the date of the Western Easter doesn’t depend on the lunar cycle as much as it once did, and so often varies from the date calculated purely from astronomical observations. Still one of the church year’s most moveable feasts, Easter Sunday in the Western tradition can fall on any date between 22 March and 25 April.

Unity and the celebration of diversity

In 1997 The Council of World Churches met in Aleppo, Syria, and proposed a method of calculating the true equinox and the ‘ecclesiastical’ or paschal full moon using the most accurate astronomical calculations but with the meridian of Jerusalem as the point of measure. However, no further progress has been made and the difference between Eastern and Western traditions remains today.

But really, isn’t it an enrichment of our common Christian heritage to celebrate Easter twice, and does it really matter which date is right? Isn’t the last thing Christians ought to do to fix Jesus’ death in time and history and shouldn’t we be concentrating on showing the relevance of his life in the present age?

Easter dates: the not-so-trivial files

Even England had its own dispute over the date of Easter. In the 6th and 7th centuries Celtic tradition Christians and Roman Augustinian Christians celebrated on different dates. The argument was settled by a Synod at Whitby which joined all English Christians to the Roman system along with the rest of Western Christendom.