Easter europen dating
No details for the computation were specified; these were worked out in practice, a process that took centuries and generated a number of controversies.
It has come to be the first Sunday after the ecclesiastical full moon that occurs on or soonest after 21 March, but calculations vary.
Easter therefore varies between 4 April and 8 May in the Gregorian calendar (the Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate).
Also, because the Julian "full moon" is always several days after the astronomical full moon, the eastern Easter is often later, relative to the visible moon's phases, than western Easter.
The First Council of Nicaea (325) established two rules, independence of the Jewish calendar and worldwide uniformity, which were the only rules for Easter explicitly laid down by the Council.
(See also Computus and Reform of the date of Easter.) In particular, the Council did not decree that Easter must fall on Sunday. The following day, Easter Monday, is a legal holiday in many countries with predominantly Christian traditions.
The scriptural instructions specify that the lamb is to be slain "between the two evenings", that is, at twilight.
By the Roman period, however, the sacrifices were performed in the mid-afternoon.
Philo, Special Laws 2.27/145 ("Many myriads of victims from noon till eventide are offered by the whole people").
This interpretation, however, is inconsistent with the chronology in the Synoptic Gospels.
It assumes that text literally translated "the preparation of the passover" in John refers to Nisan 14 (Preparation Day for the Passover) and not necessarily to Yom Shishi (Friday, Preparation Day for the Passover week Sabbath) Jewish Christians, the first to celebrate the resurrection of Jesus, timed the observance in relation to Passover.
Direct evidence for a more fully formed Christian festival of Pascha (Easter) begins to appear in the mid-2nd century.
Perhaps the earliest extant primary source referring to Easter is a mid-2nd-century Paschal homily attributed to Melito of Sardis, which characterizes the celebration as a well-established one.