Why isn’t Easter the same day every year?

I am writing this on the day before Easter, the most important holiday for Christians around the world as we celebrate the glorious resurrection of Jesus Christ. Easter came really early this year, falling right at the beginning of April. This begs the question: why, exactly, does Easter move around the calendar? Why don’t we just hold Easter on the same day every year, the way we do with Christmas?

This is a question I have answered on my blog back in 2014, but I only gave a brief overview back then, and I know that some of you Cat Flaggers have only started following me since then. Also, given how the global coronavirus pandemic robbed many of us of our traditional holiday celebrations through much of 2020, I have personally been feeling much more passionate about celebrating these holidays this year. So, I’m revisiting this topic with a deeper dive and taking a closer look at why Easter doesn’t have a fixed date and can fall almost anytime in spring.

But to understand the reason behind Easter’s moveable date, we first have to talk about Passover.

Yes, these two holidays are very much linked.

Passover is the annual Jewish celebration of the events described in Exodus 11:4-32, where God punished the ancient Egyptians for continuing to hold the people of Israel in bondage by killing the firstborn son of every Egyptian family, except the Israelites who followed Moses’s instructions to put the blood of a sacrificed animal over their door. To this day, Jews celebrate the seven-day holiday by holding a Seder, or dinner ceremony, that includes serving matzah, or unleavened bread. Like other Jewish holidays such as Hanukkah and Yom Kippur, its start date varies from year to year.

Well, actually, no. Passover always falls on the same day every year: the 15th of Nissan. See, when determining the dates of important Jewish holidays, the ancient Hebrew calendar is used. This calendar is based on the lunar cycle, and contains 12 months in most years, though a 13th is sometimes added to keep holidays in synchronization with the seasons. Hanukkah is held on the 25th of Kislev, and Yom Kippur on the 10th of Tishri.

It’s when you try to convert dates from one calendar to another that you end up with the date of a holiday appearing to move dates from year to year. This is also why Chinese New Year appears to move every year – it always falls on the first day of the year according to the traditional Chinese lunar calendar, hence the name.

Passover and Easter are very much intertwined in the Christian scriptures. According to the Gospels, Jesus was staying in Jerusalem during Passover when He held His famous Last Supper, a Passover Seder. Yes, the Holy Communion that Christians perform during their church services in reenactment of this moment is, indirectly, a reference to a Jewish holiday.

It was that Passover night that Jesus was betrayed and arrested, brought before the authorities, and sentenced to death. He was crucified like a common criminal, between two criminals who were executed along with Him on either side. The Gospels go on to describe how, on the morning of the third day after His crucifixion, a group of women who had gone to visit His tomb found it empty, and were told by two angels to spread the word to the apostles that He is Risen.

Since Easter, as the celebration of Christ’s Resurrection, is connected to Passover, is that why its celebration moves every year? Well… yes and no.

It’s time to talk about the Council of Nicaea.

On July 4, 325 AD, Roman Emperor Constantine the Great summoned Christian bishops from across his realm to settle some key questions about Christianity. After the early Christian church suffered centuries of religious persecution under Roman authorities, Constantine did a sudden about-face and was giving the young religion the sanction of the Roman state. That meant the state needed to know what Christianity, well, was.

Most of the Council’s debates were centered around the nature of Jesus, the doctrine of the Trinity, and the structure of the clergy, but for our purposes, the most important question they discussed was the date of Easter. See, up to this point, Christians had always been celebrating Easter on the Sunday closest to Passover, in recognition of the holidays’ connection. However, Constantine was an anti-Semite who demanded that Christians should have as little to do with Jews as possible. At his insistence, the date of Easter would no longer be based on a Jewish holiday. Officially. Of course, these bishops weren’t about to throw away the connection to Passover entirely, so instead of just picking a date to hold Easter every year, they devised a formula to keep the two holidays somewhat in sync.

After the Council of Nicaea, Easter was set to be held on the Sunday after the first full moon of spring. This full moon was dubbed the “Paschal Full Moon” due to its connection to the holiday. Thus, Easter can fall anywhere between March 22 and April 25.

Except that’s not the whole story, either.

It turns out that the vernal equinox, or first day of spring, varies a bit from year to year, and even between the western and eastern hemispheres. This is because the definition of the equinox is that it is the day when the sun is directly above the equator and day and night are of equal length, two phenomena that are based around the orbit and spin of our planet. The equinox can fall anytime between March 19 and 22. However, in the centuries after the Council was held, the Christian church ultimately decided to fix the “first day of spring” for the purposes of calculating Easter as March 21, the one of the feast days of St. Benedict.

Furthermore, churches in the Western tradition, such as the Catholic and Protestant churches, don’t use the actual first full moon of spring as the Paschal Full Moon either, instead using a table of “full moon dates” calculated in 1583 that predicted when the Paschal Full Moons for all future years would fall. As one might expect, these calculations were not always precise, and in many years the date used as the so-called “Paschal Full Moon” in order to calculate the date of Easter falls 1-2 days before or after the actual first full moon of spring.

A recent example of this occurred in 2019, when Western Easter would have fallen on March 24 if Western churches used the actual, scientific, astronomical vernal equinox and full moon to calculate the date of Easter, but since these churches use this Renaissance-era formula instead, Western Easter of 2019 was held on April 21.

And, yes, I specified Western Easter, since as you may have noticed on many calendars, there is also an Orthodox Easter.

Okay, seriously?

Today, the calendar that the world has adopted as its global standard for everyday use is the Gregorian calendar, devised in 1582 and first adopted by the Catholic Church by decree of Pope Gregory XIII. However, the eastern Orthodox Church has steadfastly refused to adopt this Catholic calendar, and continues to use the old Julian calendar that was used in ancient Roman times, devised by Julius Caesar.

Not only that, but the Orthodox Church also uses the actual, scientific, astronomical dates of the vernal equinox and full moon to calculate the date of Orthodox Easter each year. Together, these differences mean that Orthodox Easter usually falls on a different Sunday than Western Easter. For example, this year’s Orthodox Easter will be held nearly a month after Western Easter, on May 2 of the Gregorian calendar (April 19 of the Julian calendar). There are, however, some years where Western and Orthodox Easters fall on the same day; the next year this will happen is in 2025.

There have been some proposals to reform the date of Easter over the years, hoping to “unify” the Western and Orthodox celebrations of the holiday. One proposal would be to choose a fixed Sunday in April as the day Easter is set to be celebrated. So far, however, these are just proposals.

Whenever and however you choose to celebrate Easter, what matters in the end is the glorious gift we celebrate on that day. I wish you all a very happy Easter this year Cat Flaggers! Let us all rejoice!

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