Gregorian Calendar

Easter may occur on different dates in the Gregorian Calendar (used by Catholic and Protestant churches) and the Julian Calendar (used by the Orthodox church).

Roman Catholics use the gregorian calendar

We orthodox christians do not celebrate with Roman Catholics Easter because Roman Catholics use the gregorian calendar to calculate and decided the day in which the Eastern celebrations should occur, where we the Orthodox Christians use still the old moon calendar (which the jews used too), when Jesus was crucified.

from following the julian calendar that differs from the gregorian calendar which is used by most western countries and christian denominations

The different date for Orthodox Easter comes from following the Julian calendar, which differs from the Gregorian calendar used by most western countries and Christian denominations.

Julian calendar

Many Orthodox churches base Easter on the Julian calendar meaning that Easter is often celebrated on a different date.

different calendars

The Roman Catholic Church and the Eastern Orthodox Church assign different dates for the Lord Jesus Christ's birth and resurrection based on different calendars.

The Eastern Orthodox Church uses the older Julian calendar

The Eastern Orthodox Church uses the older Julian calendar, meaning the dates of Easter for the two sects of Christianity do not always coincide.

Passover

The difference in the determination of Easter between the Orthodox and other Christian Churches concerns the date of Passover.

Catholics following the Gregorian calendar, and Orthodox Christians following the Julian calendar

Orthodox Easter is also sometimes celebrated on different days to Catholic Easter, due to Catholics following the Gregorian calendar, and Orthodox Christians following the Julian calendar.

on the error of the Julian Calendar

But the difference in the celebration of Easter between Orthodox and Catholics is not only based on the error of the Julian Calendar but also on the error of the so-called “Metonic cycle”, named after Greek astronomer Meton of Athens of the 5th century BC.

calculated using the Gregorian calendar

The dates of the Catholic Easter are calculated using the Gregorian calendar, unlike Orthodox Easter which dates are calculated using the Julian calendar.

older Julian calendar

The date for Western Easter depends in part on phases of the moon, but Eastern Orthodox churches base their date on the older Julian calendar — and consequently often celebrate after the West.

the

Christians determine the date of Easter by one of two complicated systems (depending on the denomination).

Julian calendar and the Western churches use the Gregorian calendar

The Eastern churches calculate Easter on the Julian calendar and the Western churches use the Gregorian calendar, thus the variance in dates.

Due to the introduction of the Gregorian calendar

Due to the introduction of the Gregorian calendar, Orthodox and Roman Catholic Easter now only coincide once every several years.

at a later date than the Easter date observed by many western churches

The Orthodox Christian date for Easter Sunday often occurs at a later date than the Easter date observed by many western churches.

the Roman Julian calendar, not our modern Gregorian calendar

The Eastern Orthodox Church uses the Roman Julian calendar, not our modern Gregorian calendar, to determine these dates, so sometimes the two Easters don’t occur on the same date for that reason as well.

they count date differently from Catholics

The Orthodox church has got the different date for Easter, usually one week later, because they count date differently from Catholics.

Orthodox Easter is based on the Julian calendar, not the Gregorian calendar

Orthodox Easter always falls after Passover; Orthodox Easter is based on the Julian calendar, not the Gregorian calendar used by the Western church.

the Orthodox churches use a slightly different way of calculating the ecclesiastical full moon

This, coupled with the fact that the Orthodox churches use a slightly different way of calculating the ecclesiastical full moon, means that, in most years, the Orthodox churches celebrate their Easter on a later date than the other Christian churches.

why the Catholic Easter does not always coincide with the Orthodox Easter as Catholic church follows the Gregorian calendar while Orthodox church follows the Julian calendar that never skipped those days

This is also the reason why the Catholic Easter does not always coincide with the Orthodox Easter as Catholic church follows the Gregorian calendar while Orthodox church follows the Julian calendar that never skipped those days.