The Church celebrates the Solemnity of the Ascension of the Lord 40 days after the Resurrection, affirming the belief that Jesus, after His passion and resurrection, ascended both body and soul into heaven. The Gospel accounts agree that Jesus ascended to heaven forty days after His Resurrection, body and soul. For the Catholic Church, the Ascension of the Lord signifies not only the completion of the work of the cross but also the exaltation of human nature above all creatures.
Since ancient times, Christians have held the place on the Mount of Olives in high esteem, where Jesus is believed to have left His footprints on a stone before ascending to heaven. In the 4th century, a church was built here, followed by a monastery. In the 12th century, the crusaders erected an octagonal temple with a dome open to the sky and a fortified monastery. Later on, the Christian temple was converted into a mosque. It remains in Muslim hands to this day, but not as an active mosque, rather as a museum object that can be visited.
Originally, the Church celebrated the Ascension of Jesus together with the mystery of Pentecost. The separation of these feasts happened in 370 A.D. Today, for pastoral reasons, many countries celebrate the Ascension a few days after the actual date. The feast is moved to the penultimate Sunday of Easter instead of the Thursday 40 days after Easter.
We use the term "ascension" to describe the event we celebrate, because Christ ascended into heaven by His own power. On the other hand, Christ will take His Mother and, one day, all of us to heaven. This is why we refer to the event as the "Assumption.”