Why is Easter usually celebrated on a different date in Greece?

Did you know that Easter is celebrated in Greece on a different date to that which is marked by the Christian churches of western Europe?

The short explanation for why this is the case is that the Orthodox Christian churches (Russian and Greek, for example) still follow the Julian calendar, whereas the religions of western Europe switched to the Gregorian calendar some centuries ago. To understand how this came to be, we need look back at the introduction of the Julian and the Gregorian calendars, and how they differ.

The Julian calendar was introduced in 45 BCE by Julius Caesar, replacing the Roman calendar which was a complicated lunar calendar. The Julian calendar is a solar calendar, based on the revolutions of the Earth around the sun. It takes the Earth approximately 365.242189 days, or 365 days, 5 hours, 48 minutes, and 45 seconds, to revolve once around the Sun. This is called a tropical year, and begins on the March or vernal equinox.

It was recognised by the Julian calendar that a tropical year is greater than 365 days long. Leap years were introduced by the Julian calendar, in order to accommodate the extra portion of a day each year. If we didn’t add a leap day on 29th February every four years, each calendar year would begin about 6 hours before the Earth completes its revolution around the Sun and we would slowly see our dates not match the seasons, the disparity adding up to about 24 days in 100 years.

To begin with, there was an error with the Julian calendar in that they added a leap year every three years, but this was corrected in 12 CE. From that point on, every fourth year was a leap year. So far so good.

However, the Julian calendar allows for each year to average 365 days and 6 hours, whereas it’s actually 11 minutes and 15 seconds short of that amount, because a tropical year is actually 365.242189 days and not 365.25 days. Over a period of a hundred years, that amounts to almost 19 hours! With the passage of the centuries, it became apparent that the Julian calendar was not accurate enough.

So, the Gregorian calendar has a slightly different way to calculate leap years, in order to make up for the difference between 365.25 days and 365.242189 days and be more accurate over a long period of time. With the Gregorian calendar, once every hundred years (usually!), we skip a leap year and have a ‘common year’ instead. This will not happen within the span of most of our lifetimes, as the last time this happened was in 1900 and the next time it will happen is in 2100. Those years you would expect to be leap years, wouldn’t you? But they’re not.

Here’s how the Gregorian calendar calculates when there will be a Leap Year:

If a year is divisible by 4, it’s a leap year;

HOWEVER, if it is also divisible by 100, it is not a leap year;

UNLESS! it is also divisible by 400, in which case it is a leap year.

Got it?!

So, the years 1800 and 1900 were not leap years; but 2000 was. And the years 2100, 2200, 2300 won’t be leap years. In every four-hundred-year cycle, three leap years are skipped over. That’s how the Gregorian calendar remains truer to a tropical year than the Julian calendar. It still is not perfect, however! The Gregorian calendar is off by one day every 3,236 years when compared with the tropical year. I don’t think that’s going to present a significant problem for any of us, though.

The Gregorian calendar was introduced by papal bull in 1582. Pope Gregory XIII decreed that churches should conform to this new calendar, which required them to drop 10 days from the calendar that was in use in that time. However, the switch from Julian to Gregorian did not take place at the same time in all countries; in fact, it took from 1582 to 1927 for all countries to move over and operate from the same calendar and, of course, the later that countries joined the Gregorian calendar, the more days they needed to drop!

Greece didn’t join until 1923, by which point they needed to lose 13 days, as did Turkey in 1927, the last country to join.

Because the Julian calendar hasn’t skipped those 10-13 days, as referred to above, and because it still features a leap year every four years without a break, currently (1901–2099), the Julian calendar is 13 days behind the Gregorian calendar. After 2100, when the Gregorian calendar will miss a leap year but the Julian calendar will include one, the difference will then be 14 days.

So, to get back to the Easter question, why is Easter celebrated on different dates in the western churches as compared to the orthodox?

Well, the western Christian Easter Sunday date is calculated by finding the first Sunday after the first full moon on or after the vernal equinox. Therefore, Easter can fall as early as 22nd March and as late as 25th April, depending on when the full moon occurs. In 2021, the first full moon after the vernal equinox was on 28th March. That was a Sunday, and so, for those in the western Christian religions, Easter was the following Sunday, 4th April.

The Orthodox Easter usually falls later than the Catholic one because the Julian calendar is used. For the Orthodox churches, the vernal equinox is fixed at 21st March, although this no longer corresponds to the actual equinox in astronomical terms. However, the 21st March on the Julian calendar now falls on what those of us who are on the Gregorian calendar refer to as 3rd April! Therefore, for the Orthodox churches, they calculate their Easter date based on the date of the first full moon following 3rd April. This year, 2021, there was a full moon on 27th April and so Easter is the following Sunday, 2nd May.

That’s why Orthodox Easter can be anywhere between one and four weeks after the western Christian religions mark Easter. However, sometimes the dates coincide, if there is no full moon between the vernal equinox and the Julian calendar 21st March, ie, 3rd April. If the full moon falls after 3rd April, the two Easters coincide. This last happened in 2017 and the next time western Christian and Orthodox Easter will fall on the same date is on 20th April 2025. However, the gap is widening and, after 2700, they will never coincide again!

To summarise, as with western Christian Easter, Orthodox Christian Easter falls on a Sunday between 22nd March and 25th April. The difference is that, in the Julian calendar, their 22nd March – 25th April corresponds to 3rd April – 10th May in the Gregorian calendar. This year, Easter in Greece is marked on 2nd May; and Morgan and Olwen are delighted by the prospect of two lots of Easter eggs!

If your brain has not yet melted, you might like to check this out to find out all about the Revised Julian Calendar, an improvement on the Gregorian!

The Revised Julian Calendar (timeanddate.com)

And also here to look into what a calendar looked like in the years when dates were deleted in order to transfer from Julian to Gregorian calendar (hint: in Greece, February 1923 only had 15 days and in the UK, September 1752 was only 19 days long!):

From Julian to Gregorian Calendar (timeanddate.com)