Ascension Day is traditionally celebrated on a Thursday, the fortieth day of Easter (following the accounts given in Mark , Luke , Acts 1:2 ), although some Christian denominations have moved the observance to the following Sunday. Augustine says that it is of Apostolic origin, and he speaks of it in a way that shows it was the universal observance of the Church long before his time.
Frequent mention of it is made in the writings of St. Gregory of Nyssa, and in the Constitution of the Apostles.
Before the Vigil, the Paschal hours are said for the last time and the Paschal greeting is exchanged.
Ascension Thursday also commemorates the Holy Georgian Martyrs of Persia (17th–18th centuries). The Sunday after Ascension is the Sunday of the Holy Fathers of the First Ecumenical Council at Nicaea.
This council formulated the Nicene Creed up to the words, "He (Jesus) ascended into heaven, and sits at the right hand of the Father; and shall come again, with glory, to judge the living and the dead; Whose kingdom shall have no end." The Afterfeast ends on the following Friday, the Friday before Pentecost.
The next day is appropriately a Saturday of the Dead (general commemoration of all faithful departed).
The Eastern Orthodox Church uses a different method of calculating the date of Easter, so the Eastern Orthodox commemoration of Ascension will usually be after the western observance (either one week, or four weeks, or five weeks later; but occasionally on the same day).
During the Polyeleos at Matins, the Epitaphios, which was placed on the altar on Holy Saturday (either at Matins or the Midnight Office, depending on local custom) is taken from the altar and carried in procession around the church. At the Divine Liturgy, special antiphons are sung in place of Psalms 102 and 145 and the Beatitudes.