Easter Sunday

Easter, also called Pascha (Aramaic, Greek, Latin) or Resurrection Sunday, is a Christian festival and holiday commemorating the resurrection of Jesus from the dead, described in the New Testament as having occurred on the third day after his burial following his crucifixion by the Romans at Calvary c. 30 AD.  It is the culmination of the Passion of Jesus, preceded by Lent (or Great Lent), a 40-day period of fasting, prayer, and penance.

Most Christians refer to the week before Easter as "Holy Week", which contains the days of the Easter Triduum, including Maundy Thursday, commemorating the Maundy and Last Supper, as well as Good Friday, commemorating the crucifixion and death of Jesus. In Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the 50th day, Pentecost Sunday. In Eastern Christianity, the Paschal season begins on Pascha and ends with the coming of the 40th day, the Feast of the Ascension.

Easter and its related holidays are moveable feasts, not falling on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the Sun; its date is calculated based on a lunisolar calendar similar to the Hebrew calendar. The First Council of Nicaea (325) established two rules, independence of the Hebrew calendar and worldwide uniformity, which were the only rules for Easter explicitly laid down by the council. 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.  Even if calculated on the basis of the more accurate Gregorian calendar, the date of that full moon sometimes differs from that of the astronomical first full moon after the March equinox.     SOURCE:  Wikipedia