The Baltimore Catechism, no. 3, Lesson 8.
101. When did Christ ascend into heaven?
Christ ascended, body and soul, into heaven on Ascension Day, forty days after His Resurrection.
102. Why did Christ remain on earth forty days after His Resurrection?
Christ remained on earth forty days after His Resurrection to prove that He had truly risen from the dead and to complete the instruction of the apostles.
(a) Saint Paul tells us that Christ, after His Resurrection, appeared frequently to the apostles and to many others.
(b) Christ ascended into heaven from Mount Olivet, a hill outside Jerusalem.
103. What do we mean when we say that Christ sits at the right hand of God, the Father Almighty?
When we say that Christ sits at the right hand of God, the Father Almighty, we mean that Our Lord as God is equal to the Father, and that as man He shares above all the saints in the glory of His Father and exercises for all eternity the supreme authority of a king over all creatures.
(a) Even as man, Christ of Himself has dominion over all creation. His Kingship rests on the fact that His human nature is immediately united to the divine Person of the Son of God, and on the fact that He redeemed all men with His precious blood.
(b) On earth Christ exercises His kingly authority in spiritual matters through His Church. His Kingship extends also over temporal and civil matters.
Taken from The Basic Catholic Catechism
PART FOUR: The Apostles’ Creed VI-VIII
Sixth Article: “He ascended into heaven; He sits at the right hand of God the Father almighty”.
By Rev. William G. Most. (c) Copyright 1990 by William G. Most
Forty days after his Resurrection, Jesus ascended into heaven. During this period between his Resurrection and Ascension, He actually gave the primacy He had promised to Peter, as we read in John 21. The many events between His resurrection and ascension preclude the theory that He ascended on Easter. His ascension does not mean that heaven is somewhere up in space. This was a way of making clear that He was leaving the present mode of existence. St. Paul in Colossians 3:1 urges us to live our lives now as if we had already died, had risen, and had ascended with Him. In a mystical sense we have done that, in that our Head has done that. In the physical sense it is still in the future.
He ascended to receive the glory due to Him as conqueror of sin and death (Philippians 2:8-11); to be our Mediator and advocate with the Father (Hebrews 9:24); to send the Holy Spirit as He had promised at the Last Supper (John 16:7); and to prepare a place for us as He also promised (John 14:2).
Now He is seated at the Father’s right hand, which means that, as He said, “all power has been given to Me in heaven and on earth (Matthew 28:18). He always had that power as God, but now He exercises it as man, as King of the Universe, with His Mother beside Him as Queen of the Universe.
As God He is everywhere, but not as man, though He is present on earth most widely in the Holy Eucharist, even as man.
Besides this real bodily presence in the Eucharist, Christ is present on earth in other, lesser ways. Vatican II explained the various forms of presence, in the Constitution on the Liturgy, # 7: “Christ is always present to His Church, especially in liturgical actions. He is present in the Sacrifice of the Mass in the person of the priest; ‘He is the same one, now offering by the ministry of priests, who then offered Himself on the Cross [citing the Council of Trent].’ But He is most greatly present under the Eucharistic species. He is present by His power in the Sacraments, so that when anyone baptizes, Christ Himself baptizes. He is present in His word, for He speaks when the Sacred Scriptures are read in the Church. He is present, finally, when the Church prays and sings the Psalms, He who promised ‘Where two or three are gathered in my name, there I am in their midst'”(Matthew 18:20).