The New Testament contains two accounts of the Ascension of Christ.
The first is at the end of Luke, where it says, “[Jesus] led them out as far as Bethany, and lifting up his hands he blessed them. While he blessed them, he parted from them and was carried up into heaven” (24:50-51).
The second is found at the beginning of Acts, where we read,
And when he had said these things, as they were looking on, he was lifted up, and a cloud took him out of their sight. And while they were gazing into heaven as he went, behold, two men stood by them in white robes, and said, “Men of Galilee, why do you stand looking into heaven? This Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven” (1:9-11).
These passages would have been understood by ancient readers as recording a miracle. The Latin word miraculum means something that incites wonder—and wonder certainly would have filled the original witnesses of the Ascension.
Modern people also recognize that these passages record a miracle, but they can struggle with this event in a way the ancients didn’t. This is because our knowledge of the dimensions of the cosmos is different from theirs.
There were a number of models of the cosmos in the ancient world, but one of the things that they all agreed on is that it was small (at least, by our standards).
The most common model held that the earth was at the center of the universe, and around it was a set of nested, transparent spheres.
Directly or indirectly attached to each sphere was one of the seven classical planets: the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn. (Any light in the sky that didn’t maintain a fixed position was considered a wandering star, so the Sun and the Moon counted as “wanderers” or planétai).
The rest of the stars always maintained fixed positions with respect to one another, giving us the constellations, and these “fixed stars” were assumed to be attached to their own sphere, which was just outside the orbit of Saturn.
The sphere of the fixed stars was regarded as the ultimate boundary of our universe, and since it was just beyond Saturn, you can see that the universe wasn’t very big.
Even the Greek philosopher Archimedes, who believed in a larger universe, thought it was only two light-years across. He wrote about this in a book called The Sand Reckoner, in which he estimated how many grains of sand it would take to fill the universe. (He concluded that it would take 8 x 10^63 grains.)
For Christians, the realm beyond the fixed stars would be the realm of God—the ultimate heaven—and given the small size the universe was believed to have, it would not be difficult to imagine that when Jesus ascended, he quickly reached the ultimate heaven and sat down at the right hand of God (Heb. 1:3).
Things are more complicated for us. By 1919, many astronomers thought the universe was 300,000 light-years across and that it contained only the Milky Way galaxy. However, by 1929, Edwin Hubble had realized that the “spiral nebulae” were not part of the Milky Way but were, in fact, distant galaxies outside ours, making the universe at least 280 million light-years across.
Today we know that the visible universe is 93 billion light-years in diameter, and that’s just the part we can see. We have evidence that it’s actually at least 250 times larger than that.
This creates a difficulty for moderns. Even if Jesus left the earth and began traveling at the speed of light, he would still be well within the Milky Way galaxy, he might not even have gotten as far as the star Deneb (alpha Cygni), and he wouldn’t leave the visible universe for another 93 billion years.
A skeptic thus might mock this situation and point out that the Second Coming should occur long before then, so Jesus would have to leave earth and then turn around in space—without having reached God—to come back.
Of course, any such mocking would be premature, because on the Christian view, it is God who wrote the laws of nature, and so he’s not bound by the light speed limit. He can have Jesus move at any speed he chooses, and he can even have Jesus instantly move (teleport) to wherever he wants him to be, including heaven.
Many people think of heaven as a spiritual realm rather than a physical one, and it’s certainly not part of our physical universe. You couldn’t fly there in a starship, no matter how much faster than light it could move.
But heaven must be physical in one sense: It must be capable of at least receiving bodies, because Jesus and a few select others have their bodies with them in heaven. These bodies may not be extended in three dimensions the way objects are here on earth, but heaven must be capable of receiving them in some way, even if it’s unimaginable to us.
Given that God is omnipotent—and thus able to bring about any state of affairs that doesn’t involve a logical contradiction—we don’t need to worry about the physical limits that we are subject to or precisely how Jesus got to heaven. That’s something we can leave to God.
But how are we supposed to understand what happened at the Ascension itself? Why did Jesus rise from the earth and then disappear behind a cloud? Why didn’t he just disappear in a burst of light or something?
The answer is that a dazzling burst of light wouldn’t have communicated what God wanted the witnesses to understand. Jesus had disappeared in front of the disciples before, like how he did for the two disciples on the road to Emmaus (Luke 24:31), and it didn’t signal that the post-Resurrection appearances were over.
If Jesus had simply vanished, the disciples might have assumed that Jesus would keep appearing to them, as he had in the previous forty days (Acts 1:3), but God wanted to make it clear that now things were different. Jesus was going to God and would not simply keep appearing in bodily form.
As the Catechism says, “Christ’s ascension marks the definitive entrance of Jesus’ humanity into God’s heavenly domain, whence he will come again; this humanity in the meantime hides him from the eyes of men” (665).
His rising above the surface of the earth communicated that he was going to heaven—which was pictured as being “up” from an earthly perspective—and thus a break with Jesus’ earthly existence.
The cloud is also an important element in the symbolism God was using. Acts 1:9 says two things about what happened: “(1) he was lifted up, and (2) a cloud took him out of their sight” (ESV). The Greek word for “took” (hupolambanó) means “to cause to ascend, take up” (BDAG).
The ESV tries to smooth this out into good English, but the thought is that he was lifted up and then a cloud took him up and out of their sight.
This establishes Jesus as a cloud rider, which is an attribute of God (e.g., Ps. 68:4). Jesus also told the high priest that he would see the Son of Man “seated at the right hand of Power and coming with the clouds of heaven” (Mark 14:62), which is a reference to Daniel 7:13’s statement that “one like a son of man” came with the clouds of heaven and was presented to God.
The cloud that carries Jesus makes it clear that this is now happening: the Son of Man is being presented to God in heaven, where he will reign until his return.
It also explains why the disciples are then told, “Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven” (Acts 1:11)—i.e., riding on a cloud.
Greater familiarity with the relevant biblical texts thus makes clear the symbolism God was using and what it was communicating to the disciples.
God was not concerned with teaching them about the structure of the universe, but about what was happening with Jesus: he would not continue among the disciples, but was going to be exalted beside God until his Second Coming.
God thus drew on the symbolism that was resident in the disciples’ imaginations, and in the Jewish Scriptures and the teachings of Jesus, to make this clear.
What happened in physical terms after Jesus disappeared from their sight might be interesting for us to know (I personally suspect that it was at this point that he simply disappeared and then appeared in heaven, in whatever way heaven receives physical bodies), but it was not what God was interested in teaching, and so we must leave that matter to him.