For those who pay attention to details, a quick look at this year’s calendar shows something unusual: Easter and Eastern Orthodox Easter are on the same Sunday. Normally they are a few weeks apart.

Why does the Eastern church usually celebrate Easter on a Sunday different from the West?

The very short explanation is that Eastern churches use either the Julian calendar or since 1923 a modified Gregorian calendar, while Western churches use the Gregorian calendar. Also, since 1923, some of the Eastern Orthodox branches have used a different standard to set the date: Rather than using the Paschal full moon, they use the astronomical full moon for Jerusalem.

These changes in calendars and standards have made for discrepancies.

Here’s how we came to set the date for Easter.

Early Christians celebrated the resurrection of Jesus in every Sunday service.

Around the end of the first century, an annual observance of Christ’s death and resurrection developed for the anniversary of the Crucifixion. It occurred on the day of preparation for the Jewish Passover, 14 Nisan on the Jewish calendar, which can fall on any day of the week. Early Christians used it as a fast day that ended with a Eucharist meal called the Paschal fast. Paschal is a word used by Christians to indicate Easter and by the Jews to indicate the Jewish holiday Passover.

Controversy developed among Christians. Some people insisted the Paschal fast end on a Sunday. Others observed only the day of 14 Nisan. In 325, the Council of Nicaea set a feast date for the annual celebration. Many people try to state this simply by saying Easter is the Sunday following the first full moon after the vernal equinox.

However, the proper definition is more complex. In 325, astronomers developed tables showing the dates of full moons. These dates are called ecclesiastical full moons because, while very close to the actual dates of the astronomical full moons, the astronomers in 325 didn’t take in all the information to precisely predict movement.

One of the ecclesiastical full moons, the first full moon on or after the vernal equinox, is the Paschal full moon, and it is used to set Easter’s date.

Here the church differs slightly from astronomical definitions. The church uses March 21 as the date of the vernal equinox. March 21 was the date of the vernal equinox in 325. The astronomical equinox shifts slightly every year, always near March 21, but not always coinciding. Also, people mark Easter as it starts in their own time zone, whereas the equinox occurs at a specific moment for the entire Earth: when the sun is aligned with the Earth’s equator.

And as mentioned earlier, eastern and Western churches use different calendars.

So is it any wonder that with all this history, science and theology colliding that some people, such as the World Council of Churches (, want to change how the Easter date is set so that all Christians around the world mark it on the same day?

SOURCES: World Book; Dictionary of Christianity by J.C.Cooper,,,,,