Benedict XVI is quoted in my May Magnificat for the Feast of the Ascension as saying:
"The meaning of Christ's Ascension expresses our belief that in Christ the humanity that we all share has entered into the inner life of God in a new and hitherto unheard of way. It means that man has found an everlasting place in God." He adds that it would be a mistake to interpret the Ascension as the temporary absence of Christ from the world. Rather, "we go to heaven to the extent that we go to Jesus Christ and enter into him. Jesus himself is what we call "'heaven'."

I think we are called to feel joy on this Feast because Jesus was so joyful; He was going home to his Father. Let us rejoice and return with great joy to prayer as we wait for the Spirit to come on Pentecost to enlighten us and strengthen us!