The Solemnity of the Ascension of the Lord, a Holyday of Obligation.

“But you shall receive power when the Holy Spirit has come upon you; and you shall be my witnesses in Jerusalem and in all Judea and Samaria and to the end of the earth.”  And when he had said this, as they were looking on, he was lifted up, and a cloud took him out of their sight.
And while they were gazing into heaven as he went, behold, two men stood by them in white robes, and said, “Men of Galilee, why do you stand looking into heaven?
This Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven.”
Acts of the Apostles 1:8-11

The ascension of the Lord signified the completion of his time on earth, which is celebrated by the Church forty days after the Resurrection and ten days before the Pentecost, the coming of the Holy Spirit. Our Lord Jesus Christ gave us hope by promising that “when I go and prepare a place for you, I will come again and will take you to myself, that where I am you may be also” (John 14:3).

Feast of Ascension, a Holyday of Obligation.