"So when they had come together, they asked him, 'Lord, will you at this time restore the kingdom to Israel? He said to them, 'It is not for you to know times or seasons that the Father has fixed by his own authority. But you will receive power when the Holy Spirit has come upon you, and you will be my witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth.' And when he had said these things, 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 1:6-11 ESV).
*In several dioceses in the western U.S. we celebrate the Solemnity of Ascension on the 7th Sunday of Easter instead of the 6th Thursday. It is supposed to be on an experimental basis, but it is probably permanent. Personally, I would prefer Ascension Thursday, 40 days after Easter, etc.