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 Jewish calendar.
He said the Last Supper, which according to Christian belief is the final meal Jesus shared with his apostles before his crucifixion, was a Passover feast — which is part of an important Jewish festival.
"So Christians always had Easter right after Passover," he said. "And then at the Council of Nicaea 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."
Engler says the Church decided March 21 is the vernal equinox — or first day of spring — and Easter falls on the first Sunday after the next full 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.- VIDEO | 'Blood moon' eclipse
- VIDEO | 'Blood Moon' rising
Engler said this year is also interesting because Eastern and Western churches — Eastern Orthodox and Roman Catholic — will be celebrating Easter on the same 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.
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.
Tinu Ruparell, head of the religious studies department at the University of Calgary, says Easter’s roots in Passover — an important Jewish festival celebrating the liberation of Jews from slavery in ancient Egypt — is older than Christmas.
It commemorates the Exodus of the Israelites, which Christians believe was made possible when God inflicted 10 plagues upon the ancient Egyptians.
During the last plague, which looked to kill first-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 Passover came to symbolize a blood sacrifice.
"Symbolically, Jesus becomes the Passover lamb to save Christians from death," said Ruparell.
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 in December — or on the calendar at all — for the church's first three centuries.
Ruparell said early Christians instead chose a date that already boasted popular 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.
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."