The Scriptures which describe the event which we call the Ascension are slightly troublesome for those who read them in a very literal sense. Of the evangelists, only two record the actual event, and they disagree about the location of the event. Matthew places the event in Galilee on a mountaintop. Luke tells us that Jesus led the disciples outside of Jerusalem where he then ascended out of their sight. Luke records the event twice, once in the Gospel and again in the Acts of the Apostles. These two accounts disagree on when the event took place with the Gospel placing it on the evening of the Resurrection and Acts speaking of a period of forty days in which Jesus appeared to the disciples before returning to the Father. These seeming contradictions actually point us toward the real importance of this celebration; i.e. not as the anniversary of an historical event, but rather as a reflection upon one aspect of part of the Paschal mystery.
The Paschal mystery is composed of several events; namely, the passion, resurrection, and ascension of Jesus followed by the gift of the Spirit. The Gospels actually are fairly unanimous that these events took place over a fairly short period of time, anywhere from three to four days. Jesus was crucified and died after celebrating the Last Supper with his disciples, rose from the dead three days later, and ascended to the Father after breathing upon the disciples the gift of the Holy Spirit. The issues of where and when this all took place when we compare the various texts reveal that the evangelists are using various constructs to show that the Paschal mystery marks the end of Jesus ministry among us and the beginning of the Church.
Moses spent forty days on Mt. Sinai (or Horeb) being instructed by God in the demands of the covenant relationship that was struck after the exodus. Jesus spends forty days instructing the apostles in the demands of the new covenant.
The covenant relationship began on a mountain. Jesus ascends from a mountaintop in Galilee, perhaps the same mountain where he began his preaching ministry with the Sermon on the Mount. He was transfigured on a mountain. He was also crucified on Mt. Calvary.
Jesus ascends on a cloud. The Holy of Holies was filled with God's presence in the form of a cloud when the Ark of the Covenant was enthroned in the Temple.
Ancient religions believed that the entrance to heaven was directly above their earthly Temple. Jesus is also depicted ascending just outside of Jerusalem, the site of the Temple.
Jesus tells the women not to touch him after the resurrection because he has not yet ascended to the Father. However, he invites Thomas to touch his hands, his feet and his side when he appears once again in the upper room.
All of these details point to the fact that the evangelists are telling us that the Ascension is a celebration of God's response to Jesus' obedience. He is enthroned at the right hand of God. Before the enthronement, the disciples are commissioned to go forth into the whole world to baptize all nations. Jesus' task is finished. Ours has just begun.