Ascension Day was actually this past Thursday, but churches generally seem to translate this feast to the first Sunday following the actual day.
9 And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight.
10 And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel;
11 Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
12 Then returned they unto Jerusalem from the mount called Olivet, which is from Jerusalem a sabbath day's journey.
The picture is of an icon by Andrei Rublev. There is a film on the artist's life.