[size=medium]For more information about Easter Sunday:
Easter Sunday is the date of the annual celebration of Christ's resurrection. The aim of the Easter Dating Method is to maintain, for each Easter Sunday, the same season of the year and the same relationship to the preceding astronomical full moon that occurred at the time of his resurrection in 30 A.D.
This was achieved in 1583 A.D. using skill and common-sense by Pope Gregory the 13th, and his astronomers and mathematicians, predominantly Lilius and Clavius, by introducing their new larger (revised) Gregorian dates table. This replaced the (original) 326 A.D. table in the Julian calendar.
Easter Sunday, from 326 A.D., is always one of the 35 dates March 22 to April 25.
The Julian Calendar In the year 3961 AM, which we call 46 BC, Julius Caesar standardized the civil calendar of the Roman Empire so that it had twelve months with fixed lengths. Before then, the date depended on observations of the sun and the moon. He also introduced the concept of the leap day, which adds a day to February every four years.The Roman government used the Julian Calendar for official purposes during the events of the New Testament, but the general population continued to use their own local calendars. The month of Quintilis was renamed ‘July’ to honor him for this calendar reform.
To avoid confusion, documents intended for wide distribution often dated events by referring to the names of officials who were in office rather than by using a calendar date. The New Testament reflects this practice. Eventually the Church had to devise a method of determining the date of Easter that would work everywhere in the Roman Empire. It used the Julian Calendar for this purpose, because even though people preferred to use their local calendars, they could easily determine the date in the Julian Calendar no matter where they were.
All Orthodox churches continue to use the Julian Calendar when they calculate the date of Easter and holy days that are dependent on the date of Easter. Some Orthodox churches still use the Julian Calendar for all holy days, such as the Orthodox Churches of Jerusalem, Georgia, Russia, and Serbia and the other Slavic churches. If you have been watching the news on television, you may have noticed that Christmas was celebrated on 7 January in Serbia and Russia. That is because the Serbian Orthodox Church and the Russian Orthodox Church use the Julian Calendar for all holy days. Currently, Julian 25 December falls on Gregorian 7 January.
AM stands for anno mundi. It was the year-numbering system in use by the Romans that was later superseded by AD or anno domini.
The Gregorian Calendar By the sixteenth century, it became obvious that the Julian Calendar was out of step with the seasons, causing Easter to slip later and later in the year. In 1582, Pope Gregory revised the Julian Calendar to fix this problem, and the result is the Gregorian Calendar that we all use for civil purposes. The Western churches and the Orthodox Church of Finland use the Gregorian Calendar to calculate all holy days. The Gregorian Calendar is identical to the Julian Calendar.
The Revised Julian Calendar
Orthodox churches agree in principle that a calendar reform is highly desirable, but they deny that Pope Gregory had the authority to do it. They hold that only an Ecumenical Council can undertake an ecclesiastical calendar reform that affects the date of Easter. However, some Orthodox churches have adopted the Revised Julian Calendar, which coincides with the Gregorian Calendar for at least the next 8,000 years. They use the Revised Julian Calendar only for holy days that are not in the Easter cycle.
Regarding to the information earlier, you may also use some other methods to calculate Easter Sundays, but all are related to Paschal Full Moon (PFM) date. There are equations to calculate with a calculator, only you have to get a table of full-moon dates on hand first.
"Easter is the Sunday after the Paschal Full Moon. The Paschal Full Moon may occur from March 21 through April 18, inclusive. Thus the date of Easter is from March 22 through April 25, inclusive. The date of the Paschal full moon is determined from tables, and it may differ from the date of the the actual full moon by up to two days. This definition, along with tables, etc. ~ from Calculation of the Ecclesiastical Calendar"
In June 325 A.D. astronomers approximated astronomical full moon dates for the Christian church, calling them Ecclesiastical Full Moon (EFM) dates. {{I am not sure but from the date of history – 325 A.D., it seems referring to Julian Calendar.}}
雖然不太明白你所講的, 你是否這個意思:Christian churches in the East which were closer to the birthplace of the new religion and in which old traditions were strong, observe Easter according to the date of the Passover festival (逾越節). Orthodox Easter will be celebrated Sunday, May 1, 2005.
Passover date is also calculate by Julian Calendar.