Over the last year or so I have wondered a lot about this question, which seems to fall under what Fergus Kerr calls "philosophy of theology." That is, Christian confession of the Ascension raises a number of philosophical questions for theologians to face squarely. The Ascension also presses questions of what we mean by "heaven" and in speaking of whether and how Christ is present in the Eucharist.
One common objection to the doctrine of the Ascension in the modern era is that it seems to hinge upon a cosmology that modern science has shown to be false. But the logic of the doctrine of the Ascension does not require a view of the universe in which heaven is (literally) above the earth. I love the Orthodox icons of the Ascension precisely because the iconography suggests that the ascension entails Jesus entering God's dimension, as it were. The deep blue shape behind the ascending Jesus suggests a parting of the veil of the cosmos, affording a glimpse into the presence of the Almighty, thronging with mysterious winged creatures. Another way to think of the Ascension might be in terms of time rather than space: Jesus has entered God's future, and we await our Lord's return to bring to fulfillment that future which began dawning during his earthly ministry.
On the Feast of the Ascension, Christians celebrate the risen Jesus, in the fullness of his humanity, returning to the bosom of the Father "to receive power and wealth and wisdom and might and honour and glory and blessing" (Rev. 5:12) and to send the Holy Spirit. This Feast is about the victory of the Lamb who was slain: Vicit agnus noster, eum sequamur.