Pascha is the most important feast in the Eastern Orthodox calendar, and is better known to other Christians as Easter or the Feast of the Resurrection of Christ. In Greek and Eastern Orthodox tradition, Pascha supersedes Christmas and other holidays because it is an affirmation of the sacrifice that Christ made, and of Christ's holiness. It is preceded by Lent, a period of fasting and reflection for all Christians, and ends with a week of celebration that starts at midnight on the day of Pascha with liturgical services.
The word for Pascha is derived from the Hebrew pesach, for Passover, because the two holidays are closely linked. The Last Supper of Christ and his disciples, for example, is believed to be a Passover Seder. A few Christians would prefer to see Easter called Pascha as well, because the word for Easter is believed to originate in the name of a pagan goddess, and some Christians dislike this association.
Some people are not aware that although Pascha and Easter celebrate the same event, they are celebrated on different days since the Eastern Orthodox holy calendar is calculated using the Julian calendar, rather than the Gregorian calendar which has been adopted by the rest of the world. To add to the confusion, Gregorian dates are used when referring to Eastern Orthodox holidays, which can make a discussion of pachalion, or how Pascha is calculated, very difficult to follow.
Essentially, according to the council of Nicea, held in 326 AD, Pascha falls on the first full moon after the vernal equinox. In 326, the vernal equinox was on 20 March in the Julian calendar, and this is the date used to calculate Pascha. However, 20 March in the Julian calendar is currently 3 April in the Gregorian calendar, due to drift which has occurred due to the imprecision of the Julian calendar. As a result, Pascha and Easter fall on different days, although sometimes they may coincide. Pascha will never happen earlier than 3 April, and as time goes on, the festival will drift even further, ultimately being celebrated in the winter.
Pascha celebrations begin with a midnight service commemorating the resurrection of Christ, and follow with a large feast on the day of Pascha itself. Many nations have unique culinary traditions for Pascha. Almost every Eastern Orthodox country participates in the exchange of red eggs, which symbolize rebirth and the blood of Christ. During Pascha week, it is traditional for people to exchange the greeting “Christ is Risen!” “Truly, He is risen!” when they meet each other.