Easter is a day that is celebrated by many from going to early morning church with their fine spring clothes, to sending out gift cards, posting memes, to going out on family picnics or trips. Easter 2021 will be celebrated on Sunday April 4th. This is one week earlier than last year which was celebrated on April 12th, instead. Some may be asking what is the reason that the Easter day changes from year to year?
How do we work out when Easter will be?
The date of Easter is calculated from the first Sunday after the first full moon following the Spring equinox in March.
“The reason for this is that Easter must occur after the biblical festival of Passover, on the full moon, when Jesus was crucified,” said Professor Sacha Stern, head of the Hebrew and Jewish Studies department at University College London.
Next year the equinox will take place on its usual date of March 20th, with the next full moon on March 28th, the Sunday exactly a week before Easter.
The decision on how and when Easter should fall each year was made by the Council of Nicaea in 325 AD, the first major church council.
Why did the Council of Nicaea need to intervene?
As the crucifixion and resurrection of Jesus happened after Passover, some early Christians decided to celebrate it then – on the 14th of the month of Nisan (from the Assyrian and Hebrew calendars). This correlates with March or April in the Gregorian calendar (named after Pope Gregory XIII), which is what we use today.
Other early Christians preferred to celebrate on a Sunday because it is thought Jesus’s tomb was found on this day, according to Brent Landau, a lecturer in religious studies at the University of Texas.
The Council of Nicaea was asked to resolve this. It decided Easter should be after the first full moon following the March equinox.
Why is Easter on a different date each year?
The predominant reason why Easter falls on a different date each year is because we now use the solar, Gregorian calendar rather than a lunar one. This means the full moon occurs on different dates each year, and therefore so does Easter.
Dr Greg Brown, astronomer at the Royal Observatory Greenwich, said Easter is based on a combination of the seven-day week and the cycle of the phases of the Moon.
“The March equinox is the date when the sun crosses from the southern hemisphere of the sky to the northern hemisphere marking the beginning of spring.
“The day and night of the equinox are of approximately equal length. As neither the calendar year (365 days) nor the cycle of the phases of the Moon (29.5 days) divide evenly by the seven-day week, the date of Easter Sunday can move irregularly by up to a month, from between late March and late April.”
Why do different churches celebrate Easter on different days?
It’s down to using different calendars.
Eastern Churches (Greek and Slavic) and Oriental Churches (Syrian, Armenian, Coptic Egyptian and Ethiopian) continued using the Julian Calendar, named after Julius Caesar, even after Europe adopted the Gregorian Calendar in 1582.
“This is why even now Easter is calculated differently by the Eastern and Oriental Orthodox Churches to the Catholic and other western Churches,” said theology and religion Professor Emma Loosely, from the University of Exeter.
“Easter is only ever celebrated by all Christians on the relatively rare occasions when the two calendars align,” she added.
Easter last took place on the same day last year for both Christian Churches in 2017, but this will not happen again until 2034.