The first reading at Mass, from the Acts of the Apostles:
In the first book, Theophilus,
I dealt with all that Jesus did and taught
until the day he was taken up,
after giving instructions through the Holy Spirit
to the apostles whom he had chosen.
He presented himself alive to them
by many proofs after he had suffered,
appearing to them during forty days
and speaking about the kingdom of God.
While meeting with the them,
he enjoined them not to depart from Jerusalem,
but to wait for “the promise of the Father
about which you have heard me speak;
for John baptized with water,
but in a few days you will be baptized with the Holy Spirit.”
When they had gathered together they asked him,
“Lord, are you at this time going to restore the kingdom to Israel?”
He answered them, “It is not for you to know the times or seasons
that the Father has established by his own authority.
But you will receive power when the Holy Spirit comes upon you,
and you will be my witnesses in Jerusalem,
throughout Judea and Samaria,
and to the ends of the earth.”
When he had said this, as they were looking on,
he was lifted up, and a cloud took him from their sight.
While they were looking intently at the sky as he was going,
suddenly two men dressed in white garments stood beside them.
They said, “Men of Galilee,
why are you standing there looking at the sky?
This Jesus who has been taken up from you into heaven
will return in the same way as you have seen him going into heaven.”
