The Ascension of Jesus occurred when Jesus ascended into Heaven after his resurrection.
The Ascension of Jesus into Heaven is a biblical event narrated by both St. Mark and St. Luke.
St. Mark summarizes the event in a single verse.
The Catechism of the Catholic Church explains what happens at the Ascension of Jesus in more theological terms.
Jesus’ final apparition ends with the irreversible entry of his humanity into divine glory, symbolized by the cloud and by heaven, where he is seated from that time forward at God’s right hand.
Jesus Christ, the head of the Church, precedes us into the Father’s glorious kingdom so that we, the members of his Body, may live in the hope of one day being with him for ever.CCC 659, 666
While Jesus’ humanity may have ascended into Heaven, his abiding presence is still among us in a variety of ways, including his Real Presence in the consecrated Eucharistic bread and wine.
Catholics also believe that Jesus will come again at the end of time.