The sky vanished like a scroll that is being rolled up, and every mountain and island was removed from its place (Rev 6:14).
i) What kind of astronomical phenomenon would ancient readers associate this with description? Modern commentators aren't very helpful here, because they don't ask that kind of question. They're more into literary allusions or literary parallels. They treat the text as a mural rather than a window.
ii) I asked a Christian astronomer, who suggested that I consult ancient commentators on that passage. But the ancient commentators aren't very helpful in that regard, for they interpret the passage allegorically. The earliest extant commentary is by Victorinus, who construes the passage allegorically:
6:14. “And the heaven withdrew as a scroll that is rolled up.” For the heaven to be rolled away, that is, that the Church shall be taken away.
Tychonius takes a similar view, according to which it symbolizes the underground church, which withdraws from public view during times of persecution. Oecumenius thinks it refers to angels.
Andrew of Caesarea construes it allegorically:
"That heaven is rolled out like a scroll symbolizes either that the second coming of Christ is unknown...or that even the heavenly powers grieve for those who have fallen from the faith as though they experience a certain rolling out through sympathy with grief. However, this image symbolizes also taht the substance of heaven does not disappear. but as though by a kind of unrolling changes into something better."
William C. Weinrich, ed. Revelation (Ancient Christian Commentary on Scripture), 98-99.
So none of them construe the astronomical image realistically.
iii) One might try to cut the knot by saying the passage is figurative. But even if that's the case, we still need to ask what figurative image the passage is meant to conjure up in the minds of the reader.
iv) Moreover, I doubt it's accurate to say the passage is figurative overall. The bit about the scroll is figurative, but that's epexegetical. The simile is used to illustrate the prosaic statement that "the sky vanished." If, therefore, the vanishing sky is compared to a metaphor, the vanishing sky is not, itself, a metaphor.
v) Admittedly, this is something John saw in a vision. So it may not be realistic. It may be dream-like. But there's still the question of what John saw.
vi) Moreover, the vision has a referential dimension. It signifies real-world events of some sort or another. That may or may not be astronomical in reality, but the question is worth exploring.
viii) Since, in Bible history, God does sometimes use real prodigies, we shouldn't rule that out.
ix) The Greek verb is ambiguous. It could mean the sky was "split" apart or split in two. Is one rendering preferable to another in context?
x) To say the sky "vanished" (or "disappeared") could either mean the sky ceased to exist or else the sky ceased to be visible. On the latter interpretation, the sky still existed, but could no longer be seen.
xi) Liberal scholars suppose ancient Jews and gentiles thought the sky was a solid dome. Let's play along with that identification for the sake of argument. On that view, to say the sky "vanished" might mean God removed the dome separating what's under the dome (the earth) from what's behind the dome.
What would be the consequences of that action? Well, on that view, wouldn't removing the dome cause everything above it to come crashing down? The cosmic sea would empty onto the earth. The celestial palace or temple would fall to earth. Likewise, earthbound observers could see God, the saints, the angels, and so forth.
But Rev 6 doesn't say that's the effect of v14. And, indeed, if all that happened, there wouldn't be much left to recount after the dust settles.
xii) On that view, the sky splitting has similar consequences. If the dome split apart or split in two, everything behind the dome would become visible. The cosmic sea would inundate the earth. But that's not the aftermath of what happens in Rev 6. So much for the solid dome.
xiii) Perhaps it means the sky disappeared from view. It was still there, but invisible to the naked eye. Is so, what does that mean?
There's a bit of a paradox here. If they can't see the sky, what do they see in its place?
We might start by asking what makes the sky visible in the first place. Illumination and contrast. Seeing the sky in relation to the horizon.
You can't see the sky in a blizzard. You can't see the sky on a foggy day.
Likewise, if you look in a mirror, you don't see the mirror itself, but whatever it reflects. If the sky became reflective, you'd see the earth when you gaze overhead. But the text doesn't say that.
By the same token, you don't see clear glass; rather, you see through clear glass. If the sky became transparent, it would become a window. You could see everything beyond the sky. But the text doesn't say that.
Another possibility is if the sky goes dark because the sun, moon, and stars go dark. If God were to miraculously shield the earth from their light (or at least the visible spectrum), then the sky would disappear from view. Indeed, the entire earth would be plunged into darkness–apart from firelight (or electrical lighting, if we construe this futuristically).
And that could be a realistic scenario. Perhaps God will block out the light.
xiv) What about the sky splitting in two? That could be the opposite effect. If something brighter than the sky appeared in the middle of the sky, like a brilliant band, it would visually bisect the sky. Because the sky would be darker on either side of the luminous boundary, it would appear as though the sky was splitting apart (or splitting in two), to reveal something behind the sky. An optical effect. Something emerging from the sky, like a bright line or crease in the sky. The edge of something incoming. Long and luminous.
Nowadays, we're used to seeing contrails. That's another, albeit modern, atmospheric phenomenon that bisects the sky.
The upshot is that we don't know for sure what the text depicts. But we can consider a range of options.