The New Testament treats the Ascension as an integral part of the Easter event.
It is the final appearance Jesus’ physical and resurrected presence on earth. It is the final component of the paschal mystery, which consists also of Jesus’ Passion, Crucifixion, Death, Burial, Descent Among the Dead, and Resurrection.
Along with the resurrection, the ascension functioned as a proof of Jesus’ claim that he was the Messiah. The Ascension is also the event whereby humanity was taken into heaven. There is a promise he will come back again.
So when is it ? The Ascension in Luke 24 is on Easter Sunday evening or, at the latest, the next day; in John 20, sometime between the appearance to Mary Magdalene (who is told not to touch the risen One because he has not yet ascended) and the appearance to Thomas (who is invited to touch him); in Acts 1, after the forty days (which, however, are symbolic of the time of revelation; there may be no intention to suggest that the ascension actually “occurred” on the fortieth day). We celebrate Ascension on the 40th day.
The main scriptural references to the Ascension are Mark:16:19, Luke:24:51, and Acts:1:2 and vvs. 8-10. Luke 24 says "While he was blessing them, he withdrew from them and was carried up into heaven". In Acts " he was taken up to heaven, after giving instructions through the Holy Spirit to the apostles whom he had chosen." Jesus commissions his followers, rather than simply blessing them; and we have an appearance from two men in white robes.
Mount Olivet, near Bethany, is designated as the place where Christ left the earth. The feast falls on this Thursday, May 18 and it is one of the most solemn in the calendar, ranking with the feasts of the Passion, Easter and Pentecost.
In disappearing from their view "He was raised up and a cloud received Him out of their sight" (Acts 1:9), and entering into glory He dwells with the Father in the honur and power denoted by the scripture phrase."
In a way, Jesus’ abandonment of the disciples upon the Mount of Olives is more profound than their abandonment on Calvary. After all, the disciples themselves predicted he would die. But no one could have imagined the Resurrection and the extraordinary forty days during which Jesus dwelled again with his friends. Forty days with the resurrected Jesus – appearing in the upper room, along the way to Emmaus, upon the beach at Galilee! Imagine their despair when this, the Jesus present to them in such an astonishing way, enters the Cloud on the Mount of Olives.
The Rev. Suzanne Guthrie writes, "The Church gives us ten days to practice dwelling in the ambiguous time between the Resurrected-Christ-vanished, and the Holy Spirit not-yet-come. In the mystical life, Ascensiontide is the Dark Night of the Soul, the anguished sense of abandonment after a solid period of union. The soul can not cling even to this union. The last threads of attachment must be broken in the darkness of unknowing before the completion of the Christian transformation – being “sent” into the world as bearers of Love."
Although no documentation of it exists prior to the beginning of the fifth century, St. Augustine says that it originated with the Apostles, and that it was observed by the Church long before his time. The Ascension is frequently mentioned in the writings of St. John Chrysostom, St. Gregory of Nyssa, and in the Constitution of the Apostles. Perhaps, prior to the fifth century it was commemorated in conjunction with the feasts of Easter or Pentecost.
Connected with this feast were the customs of: the blessing of beans and grapes (after the Commemoration of the Dead in the Canon of the Mass), the blessing of first fruits, (afterwards done on Rogation Days), the blessing of a candle, the wearing of mitres by deacon and subdeacon, the extinguishment of the paschal candle, and processions with torches and banners outside the churches to commemorate the entry of Christ into heaven. In some churches, the Ascension was depicted by elevating the figure of Christ above the altar, through an opening in the roof. In others, the figure of Christ was made to ascend and that of the devil was made to descend.