Why doesn't Easter have a fixed date?

Editor's Note: This story was first published in 2014, so the moon cycles referenced are for that year.

Easter and Christmas are both very important Christian holidays, but while families always gather on Dec. 25 in the winter, the annual spring celebration changes drastically each year on our calendars.

Steven Engler, a professor in religious studies at Mount Royal University, says the basic reason the two differ is because Christmas is fixed to a solar calendar, near the winter solstice, and Easter is based on the lunar cycles of the Jewishcalendar.

He said the Last Supper, which according to Christian belief isthe finalmeal Jesusshared with his apostlesbeforehis crucifixion,was a Passover feast which is part of animportant Jewish festival.

"So Christians always had Easter right after Passover," he said. "And then at the Council ofNicaea in the fourth century, Christians decided to separate themselves from the timing of the Jews on that, so ever since then Passover and Easter have been independent, but they're both in the spring."

Englersays the Church decided March 21 is the vernal equinoxor first day of spring and Easter falls on the first Sunday after the nextfull moon.

"Spring starts on [March 21] and you wait for the next full moon, and the next Sunday is Easter," he said.

"That's why is varies so much. This year it's later because it sort of took longer to get to that first full moon after the beginning of spring."

The first full moon after spring this year happened to be the rare "blood moon" on April 15.

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Engler said this year is also interesting becauseEastern and Western churches Eastern Orthodox and Roman Catholic will be celebrating Easter on thesame day.

"This year,[two billion] people on the planet are thinking about what they see as the key moment in history when Jesus rose from the dead," he said.

Fixed date proposed, but rejected

A fixed date has been proposed many times over the years, even as recently as five years ago, but has always been rejected.

Tradition is strong in religions.- Religious Studies professor Steven Engler

Engler says keeping with tradition of what is called the "movable feast," which does not fall on a fixed date in the Gregorian or Julian calendars, was too important.

"Tradition is strong in religions," he said.

About 400 years ago, Engler says the Western Christians decided to revise the Julian calendar which meant having three fewer leap years every four centuries. Because of that slight alteration, the two calendars are slowly diverging and the Julian calendar drifts forward.

"There were a number of people who didn't like the idea that Easter was slowly getting later and later and many centuries from now Easter would start wandering into May or June and be a summer festival," said Engler.

"So the Gregorian calendar corrected that slight drift, which keeps Easter closer to the beginning of spring."

Eastern churches use the Julian calendar still, while Western churches use the Gregorian calendar today.

Passover roots

Tinu Ruparell, head of the religious studies department at theUniversity of Calgary, says Easter's roots inPassover an important Jewish festivalcelebrating the liberation of Jews from slaveryinancient Egypt is older than Christmas.

It commemorates the Exodus of the Israelites, which Christians believe was made possible when Godinflicted 10plaguesupon the ancient Egyptians.

During the last plague, which looked to killfirst-born sons,Israelites were instructed to mark the doorposts of their homes with the blood of a slaughtered spring lamb so the spirit of God would pass over their home and sons.

"That is literally why it was called Passover,"said Ruparell.

He said Passovercame to symbolize a blood sacrifice.

"Symbolically, Jesus becomes the Passover lamb to save Christians from death," saidRuparell.

He says Christmas, the celebration of Jesus' birth, also gets its roots from other religions.

"No one really knows when Jesus was born," he said.

Christmas wasn't inDecember or on the calendar at all for the church's first three centuries.

Ruparellsaid early Christians instead chose a date that already boastedpopular festivals.

The eventual choice of Dec. 25 reflects the Christian concern about pagan gods and the winter solstice, which was traditionally held a few days earlier.

Growing retail trend?

As for why Easter bunnies, eggs and flowers became so popular,Ruparell says in the last couple of centuries they became symbols of spring and rebirth.But slowly the holiday has become a victim of commercialization.

Chocolate eggs and bunnies have long been stocked on shelves, but it seems more families are buying big gifts and toys for the kids on Easter and retailers are eager to hop on board.

"Easter has now become the fastest growing holiday behind Halloween, and it is right behind Christmas in terms of giving toys now," said Debi Andrus, an assistant professor in marketing at the University of Calgary.

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The holiday is often celebrated by family gatherings and church attendance, but some also enjoy the spirit of giving.

"Some families just do Easter egg hunts. My family's always done presents too. We call it the other Christmas," said Calgary resident Alyssa Butterwick.

But who's driving this trend?

"Is it the consumers who want something or is it the retailers stimulating demand?" said Andrus. "So that's the issue of which comes first: the chicken or the egg."

One Calgary store is promoting ethical spending for Easter.

"We don't want to discourage people from giving, but there are definitely ethical ways of giving when you're shopping," said Jason Fehr of Ten Thousand Villages.

"If you buy a fair trade product you can give to the person you're giving to, but you can also give to the person who's making the product."