On the Fortieth Day of Easter (a Thursday, or on the Sunday following), most of the world's Christians observe the Feast of the Ascension. In Catholicism, it is a Holy Day of Obligation. Elsewhere in the Christian world, liturgical Protestantism usually acknowledges the Ascension, while relatively less liturgical Protestant traditions mostly do not.
Every year when I recall the Ascension, I intend to write an essay arguing that for many Christians, more theology may hinge on the Ascension than even on the Resurrection. For one thing, if you believe in penal substitutionary atonement, it seems to me that the Crucifixion does most of the heavy lifting, not the Resurrection. Also, if your eschatological expectations involve a reversal of the Ascension, then the Ascension is necessarily a vital part of your theology. (It also becomes a vital part of your cosmology, which is where major problems arise.)
In a sense, it's probably fortuitous (and it may be intentional) that nonliturgical traditions tend not to emphasize the Ascension of the Lord. It's one of those things that maybe they don't want people to think too hard about. Yet the Apostles' Creed and the Nicene Creed affirm the (presumably literal, bodily) Ascension of Jesus into Heaven (wherever that is), and I have always had the sense that the majority of Christians believe this supernatural event in its literal, bodily sense.
Of course, the Ascension has multiple very ancient attestations. Yet many scholars surmise that the narrative also served the function of discrediting second-coming stories that arose in the early communities.
In my adult life, I have not believed in a literal/material/physical Ascension. I always try to imagine what I am supposed to see if these events were recorded on video tape. For instance, what would it look like to view the insemination of the Blessed Virgin under a microscope? The Resurrection is actually easier to imagine and visualize. If i was watching a Paranormal Activity-style video of the Holy Sepulchre that first Easter Day, I have a good idea of what I am supposed to see. But the Ascension is the most difficult of all, I think. What happened to Jesus' molecules?
The German Lutheran theologian Rudolf Bultmann famously said:
"The cosmology of the NT is essentially mythical in character. The world is viewed as a three-storied structure, with the Earth in the center, the heaven above, and the underworld beneath. Heaven is the abode of God and of celestial beings -- angels… No one who is old enough to think for himself supposes that God lives in a local heaven."
Lately I have been re-reading Karl Rahner, who was probably the most significant Catholic theologian of the 20th century. His systematic theology is a very serious engagement with philosophy and is traditional in a sense, but takes much of the Bible's supernaturalism to be non-literal. He boils his magisterial Foundations of Christian Faith down to three brief creeds.
In his Missio Alliance blog post on the Ascension, Nathan Clair offers this judiciously selected quotation from Rahner:
"The Ascension is a festival of the future of the world. The flesh is redeemed and glorified, for The Lord has risen for ever. We Christians are, therefore, the most sublime of materialists.”
As a very young and very liberal theology student, I was relieved to discover scholars with serious academic and ecclesial standing affirm a Christianity I could believe honestly and with integrity. After quite a few years away from church and faith, my recent re-engagement with Christianity has been somewhat more traditional (especially my appreciation for the Catholic intellectual tradition), but, on the matter of the physical historicity of supernatural events, no more literalist than before.
While I harbor no animus against (and frankly, I often envy) people who believe in the literal/historical/physical/material veracity of these stories, my view is that physical realities and spiritual realities are not the same. That's not to say we shouldn't be mystics. And it's nothing against the ancients, who used the only cosmology they had to account for things they could not otherwise explain. But I believe we rob these stories of their spiritual depth when we insist on literalizing ineffable truths.