April 5, 2015
Happy Easter! Ever Wonder Why The Holiday Is On A Different Date Each Year? Here's Why

Happy Easter! Today, hundreds of millions of Christians throughout the world will be observing the religion's holiest day - the day that Jesus Christ, according to Christian teaching, rose from the grave.

Unlike Christmas or the Fourth of July, which fall on the same day every year, Easter is one of those holidays that moves around a bit. Some holidays, like Martin Luther King, Jr. Day or Columbus Day, can be fudged by a few days here or there to give you a long weekend. Others, like Thanksgiving or Mother's Day, can move by as much as a week. But Easter is all over the map: the earliest possible date for Easter is March 22, and the latest is April 25; that's a full 34 days (over a month) of wiggle room!

The reason Easter moves around so much has to do with an ancient compromise involving two religions, three timekeeping systems, and a Fourth-Century understanding of the Solar System. Confused? You won't be (or maybe you still will be) after reading the rest of this post.

The New Testament teaches that Jesus died on the Friday after the Jewish festival of Passover, according to The Economist, and rose from the grave the following Sunday. The problem with assigning that event to a specific date on the modern calendar is this: our calendar is based on the ancient Roman method of timekeeping, which is based solely on the Earth's rotation around the Sun. Judaism's calendar considers the phases of the Moon into the equation, and observes Passover according to both the Moon and the Sun. Specifically, Passover is observed on the date of the first full moon following the Vernal (Spring) Equinox - that is, March 20.

Since the lunar cycle is 29 days (more or less), that gives us a 30-day range on which Passover could fall: March 21 - April 20. But there's another complication, as far as Christians are concerned: since the New Testament teaches that Jesus arose on a Sunday, fixing the date to Passover doesn't solve the problem.

By 325 A.D. Christians were celebrating Christ's resurrection on different dates, based on either figuring out the date for themselves or asking their Jewish friends to help out, and Pope Sylvester I was having none of that. The Council of Nicea convened and, among other issues, reached a compromise for calculating the date of Easter that most Christians still observe to this day: Easter is to be observed on the first Sunday following the first full moon following the Vernal Equinox, according to Time and Date.

Christendom has tweaked the system a bit here and there over the centuries, and there a couple of arcane what-if's in the system that are too complicated to explain in this post. But at the end of the day, the earliest date Easter could occur will be March 22 (last happened in 1818, won't happen again until 2285); and the latest possible date could be April 25 (last happened in 1943, won't happen again until 2038).

Unless, that is, you're one of the approximately 240 million Christians throughout the world who observe Eastern Christianity (the vast majority of the world's Christians, including the overwhelming majority of the Christian population in the United States, observe Western Christianity). Because Eastern Christianity observes the older Julian calendar to calculate its holy dates, rather than the Gregorian calendar which hangs on your wall (or more likely, is programmed into your mobile device), giving a completely different possible range of dates for Easter.

None of this, however is likely to mean anything to the millions of children around the country traipsing through the yard in their Sunday best looking for Easter eggs and enjoying Easter candy.

[Image courtesy of: Shutterstock/BlueOrange Studio]