Easter and the holidays that are related to it are moveable feasts which do not fall on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the sun; rather, its date is determined on a lunisolar calendar similar to the Hebrew calendar.
It has come to be the first Sunday after the ecclesiastical full moon that occurs on or soonest after 21 March, but calculations vary.
Most Christians refer to the week before Easter as "Holy Week"—it contains the days of the Easter Triduum, including Maundy Thursday, commemorating the Maundy and Last Supper, In Western Christianity, Eastertide, or the Easter Season, begins on Easter Sunday and lasts seven weeks, ending with the coming of the fiftieth day, Pentecost Sunday.
In Eastern Christianity, the season of Pascha begins on Pascha and ends with the coming of the fortieth day, the Feast of the Ascension.
Icon of the Resurrection, with Christ having kicked down the gates of Hades and pulling Adam and Eve out of the tombs.
Christ is flanked by saints, and Satan—depicted as an old man—is bound and chained.