Why Easter dates change every year. (Courtesy)

It's Easter once again. A time when believers get to celebrate the death, crucifixion, and resurrection of Jesus Christ.

However, have you ever wondered why, unlike other Christian holidays, say Christmas, celebrated on December 25, Easter dates change every year, hence the name 'movable feast.'

If you haven't realized, the Easter holiday usually falls anytime between March 22 and April 25. This year, Easter Sunday falls on April 4.

How Easter is determined

The lent season (period of 40 days which comes before Easter in the Christian calendar), is usually based on the Lunar calendar, unlike other holidays which are based on the Gregorian Calendar.

The lunar calendar is based on the moon phases, while the Gregorian Calendar is based on the sun phases.

Usually, Easter falls on the first Sunday after the first Paschal moon, either on or soon after the vernal equinox, which is the first equinox of the year. Once the full moon date is set, then it's easy to determine when Easter will be.

Why do the dates change every year? 

Easter dates are determined by the Pascal full moon, which can fall on various days in different time zones.

According to the Bible, the death and resurrection of Jesus Christ took place during the Jewish Passover. This was celebrated on the first Pascal moon on or soon after the vernal equinox.

According to an article on ThoughtCo, in 1583, there was a table that astronomers recorded to determine all the future Ecclesiastical full moons.

Ecclesiastical rules are that the Easter Sunday date falls on the first Sunday after the first full moon following the spring equinox, which is fixed on March 21. This is after the Christian church decided to simplify the process of calculating the Easter dates, despite the equinox dates changing over time.

This means that Easter can never take place before March 22 or any date after April 25.

In 2020, the Easter Sunday date fell on April 12, this year, it will take place on April 4, and in 2022, the Easter Sunday will fall on April 17.

In 2016, the Archbishop of Canterbury, Justin Welby said he hoped that churches would agree to having the Easter dates fixed soon, following discussions between the leaders of different Christian denominations.

Pope Francis also said that he was open to the idea of having the Easter Sunday date fixed to avoid confusion.