While the ascension of Jesus is clearly mentioned in the New Testament, some biblical scholars debate when Jesus ascended into Heaven.
For example, the Gospel of Mark does not separate Jesus’ ascension from his resurrection by any number of days.
He simply mentions, “So then the Lord Jesus, after he spoke to them, was taken up into heaven and took his seat at the right hand of God” (Mark 16:19).
This follows a few events that occurred on the day of the resurrection, making some biblical scholars say that Jesus ascended into Heaven on the day of the resurrection.
Interestingly, St. Luke also narrates the ascension in his Gospel in a similar way, not giving any time span: “Then he led them [out] as far as Bethany, raised his hands, and blessed them. As he blessed them he parted from them and was taken up to heaven” (Luke 24:50).
However, St. Luke adds to the story in the Acts of the Apostles, specifically mentioning “40 days.”
[Jesus] presented himself alive to them by many proofs after he had suffered, appearing to them during forty days.Acts 1:3
This could be a symbolic way of counting the number of days Jesus stayed with his apostles after the resurrection, or it could be a literal 40 days.
The Catholic Church decided early on to celebrate the solemnity of the Ascension of Jesus 40 days after Easter.
Whatever the case may be, the key is to see the ascension of Jesus in connection to the resurrection and that it is a historical event that happened almost 2,000 years ago.