This was designed to exactly match the Gregorian calculation.

# Its date varies from year to year ( by the Western system of calculation, it can fall on any of 35 different dates of the Gregorian calendar ).

The majority of Orthodox Christians ( Russians, in particular ) follow the Julian Calendar in calculating their ecclesiastical feasts, but many ( including the Ecumenical Patriarchate and the Church of Greece ), while preserving the Julian calculation for feasts on the Paschal Cycle, have adopted the Revised Julian Calendar ( at present coinciding with the Gregorian Calendar ) to calculate those feasts which are fixed according to the calendar date.

The Western calculation uses the Gregorian calendar, while the Eastern calculation uses the Julian calendar, whose 21 March now corresponds to the Gregorian calendar's 3 April.

This determination of starting moment is more accurate than the Gregorian calendar as far as predicting the date of the vernal equinox is concerned because it uses astronomical calculation rather than mathematical rules.

Computus ( Latin for " computation ") is the calculation of the date of Easter in terms of the Gregorian calendar or Julian calendar.

When the Gregorian calendar reform was instituted in 1582, the lunar cycle previously used with the Julian calendar to complete the calculation of Easter dates was adjusted also, in accordance with a ( modification of a ) scheme devised by Aloysius Lilius.

Calculating the calendar of a previous year ( for the Gregorian calendar taking account of the week ) is a relatively easy matter when Easter Sunday is not included on the calendar.

Eastern Christianity bases its calculations on the Julian calendar whose 21 March corresponds, during the 21st century, to 3 April in the Gregorian calendar, in which the celebration of Easter therefore varies between 4 April and 8 May.

Easter and the holidays that are related to it are moveable feasts, in that they do not fall on a fixed date in the Gregorian or Julian calendars ( both of which follow the cycle of the sun and the seasons ).

In Western Christianity, using the Gregorian calendar, Easter always falls on a Sunday between 22 March and 25 April, inclusively.

Easter therefore varies between 4 April and 8 May on the Gregorian calendar ( the Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate ).

Among the Oriental Orthodox some churches have changed from the Julian to the Gregorian calendar and the date for Easter as for other fixed and moveable feasts is the same as in the Western church.

Since 1582, when the Catholic Church adopted the Gregorian calendar while the Eastern Orthodox and most Oriental Orthodox Churches retained the Julian calendar, the date on which Easter is celebrated has again differed.

Their starting point in determining the date of Orthodox Easter is also 21 March, but according to the Julian reckoning, which currently corresponds to 3 April in the Gregorian calendar.

Accordingly, Gregorian Easter can fall on 35 possible dates — between 22 March and 25 April inclusive.

In determining the date of the Gregorian and Julian Easter a lunisolar cycle is followed.

However, the differences in the rules between the Hebrew and Gregorian cycles results in Passover falling about a month after Easter in three years of the 19-year cycle.

In years 2200 – 2299, for example, the start of Passover will be about a month later than Gregorian Easter in four years out of nineteen.

Because the Julian calendar's implicit solar year has drifted further over the centuries than those of the Gregorian or Hebrew calendars, Julian Easter is a lunation later than Gregorian Easter in five years out of nineteen, namely years 3, 8, 11, 14, and 19 of the Christian cycle.

The Concordat of 1801 re-established the Roman Catholic Church in France with effect from Easter Sunday, 18 April 1802, restoring the names of the days of the week with the ones they had in the Gregorian Calendar, while keeping the rest of the Republican Calendar, and fixing Sunday as the official day of rest and religious celebration.

The Gregorian calendar was designed to keep the vernal equinox on or close to March 21, so that the date of Easter ( celebrated on the Sunday after the 14th day of the Moon — i. e. a full moon — that falls on or after March 21 ) remains correct with respect to the vernal equinox.

The civil versions of the Julian and Gregorian Calendars are solar, because their dates do not indicate the moon phase — however, both the Gregorian and Julian calendars include undated lunar calendars that allow them to calculate the Christian celebration of Easter, so both are lunisolar calendars in that respect.

While some Eastern Orthodox national churches have accepted the Gregorian calendar dates for feast days that occur on the same date every year, the dates of all movable feasts ( such as Easter ) are still calculated in the Eastern Orthodox churches by reference to the Julian calendar.

However, all Eastern Orthodox churches rejected this rule and continue to use the Julian calendar to determine the date of Easter ( except for the Finnish Orthodox Church and the Estonian Orthodox Church which now use the Gregorian Easter ).

At Paris, he was influenced by the Gregorian Reform ideals of churchly independence from Monarchical rule.

The second section, detailing the Gregorian mission of Augustine of Canterbury was framed on the anonymous Life of Gregory the Great written at Whitby.

Due to the change from the Julian calendar to the Gregorian calendar, Bealltainn in Scotland was commonly celebrated on 15 May while in Ireland " Old Beltane " or " Old May " began about the night of 11 May.

The week cycle was not even interrupted when 10, 11, 12, or 13 dates were skipped when the Julian calendar was replaced by the Gregorian calendar by various countries.

This was known as the Gregorian Reform, which takes its name from Pope Gregory VII, ( 1073 – 85 ).

The Chinese calendar was also called the " old calendar " ( 舊曆 / 旧历 ) as opposed to the " new calendar " ( 新曆 / 新历 ), i. e., the Gregorian calendar, was adopted as the official calendar.

) So, the shift in the date of the equinox that occurred between the 4th and the 16th centuries was annulled with the Gregorian calendar, but nothing was done for the first four centuries of the Julian calendar.

In 1872, the Meiji government proclaimed 11 February 660 BC, in the Gregorian calendar the foundation day of Japan, which was then commemorated as the holiday Kigensetsu (" Era Day ") until 1948.

Western musical notation was originally created to preserve the lines of Gregorian chant, which before its invention was taught as an oral tradition in monastic communities.

Of all the Gregorian Reforms which were embodied by Lateran I, celibacy of the clergy was the most successful.

The leap year was called Sextile, an allusion to the " bissextile " leap years of the Julian and Gregorian calendars, because it contained a sixth complementary day.

According to the Julian calendar and Annunciation Style of enumerating years, then in use in the British Empire, Washington was born on February 11, 1731 ; when the Gregorian calendar was implemented in the British Empire in 1752, in accordance with the provisions of the Calendar ( New Style ) Act 1750, his birth date became February 22, 1732.

By 1704 the Julian calendar was eleven days behind the Gregorian, and the siege thus began on 21 July according to the Julian.

This discrepancy was corrected by the Gregorian reform, introduced in 1582.

Justus was an Italian and a member of the Gregorian mission sent to England by Pope Gregory I.

In 1984, after 36 years in India, Dupuis was called to teach Theology and Non-Christian Religions at the Gregorian University of Rome.

It was eventually supplanted by the Gregorian chant in the 11th century.