Stumbling out from beneath the 45-tonne bronze cone of London's planetarium, unsteady from a virtual voyage through the solar system and beyond, you can picture the earth turning beneath your feet. Stand there on the brow of the hill in Greenwich Park, your head still full of planets spinning on their computer-generated orbits, with the National Maritime Museum, the curve of the river, Canary Wharf and all the city stretched out beneath you, and the vista seems to roll inexorably east towards the curtain of night. Darkness is an inescapable fact of life on earth, an astronomical certainty which, for all the terror it brings in childhood, gives our daily existence its rise and fall, its ebb and flow, as night follows day follows night.

But what if it wasn't like that? What if night were not only dense and all-encompassing, but also sudden and unexpected? What if daylight were so pervasive, so constant, that total darkness was unimaginable, inconceivable? What if there were no one to teach us how not to be afraid of the dark?

In his 1941 short story "Nightfall", Isaac Asimov takes us to Lagash, a planet deep in a globular cluster surrounded by not one, not two, not three – but six nearby stars. When Alpha sets, Beta is at zenith; when Gamma is at aphelion, Delta is near. The whole planet is bathed in perpetual sunlight from its constant companions, so that the inhabitants of Saro City have never seen the stars, have never known the total darkness of night. Until now.

The story opens at Saro University on the eve of the first night in 2049 years, as a rare alignment of stars and planets is set to send half the world into darkness for "well over half a day". As Gamma sets, leaving only blood-red Beta hanging in the skies, the scientists who have predicted the eclipse which will plunge the world into chaos are preparing their instruments and attempting to master their rising panic.

"Imagine darkness – everywhere. No light, as far as you can see. The houses, the trees, the fields, the earth, the sky – black! And stars thrown in, for all I know – whatever they are. Can you conceive it?"

"Yes, I can," declared Theremon truculently.

And Sheerin slammed his fist down upon the table in sudden passion. "You lie! You can't conceive that. Your brain wasn't built for the conception any more than it was built for the conception of infinity or of eternity. You can only talk about it. A fraction of the reality upsets you, and when the real thing comes, your brain is going to be presented with the phenomenon outside its limits of comprehension. You will go mad, completely and permanently! There is no question of it!"

According to Asimov, the idea came from discussing a quotation from the opening of Ralph Waldo Emerson's essay, Nature with the editor of Astounding Science Fiction, John W Campbell Jr. "If the stars should appear one night in a thousand years," suggested Emerson, "how would men believe and adore, and preserve for many generations the remembrance of the city of God which had been shown!" It seemed much more likely to Asimov that the sudden majesty of the heavens would inspire fear instead of wonder. After two millennia of constant sunshine on Lagash, the terror of complete darkness, the "soul-searing splendour" of the mysterious stars, is enough to send the citizens mad, to consume civilisations in the hungry flicker of the only means to hand for making light: fire.

Asimov answers Emerson's transcendentalism by setting up an opposition between the scientists (good), struggling to understand celestial mechanics without being able to see much in the way of heavens, and the Cultists (bad) whose Book of Revelations, woven from "the confused incoherent babblings of half-mad morons", foretells a cave which will devour Lagash and send down heavenly fire to rob men of their souls. Will the astronomical truths discovered at Saro University survive the apocalypse and enlighten the survivors of the next cycle, or will the obscurantism of religion prevail? It's a confrontation that reads all the more urgently now, 70 years on, as climate scientists struggle to make their warnings of catastrophe heard above the voices of the deniers.

While the names with numbers – Beenay 25, Aton 77 – the lack of women and an honourable reporter who declines the chance to scarper when things get hairy ("I'm a newspaperman and I've been assigned to cover a story. I intend covering it.") give "Nightfall" something of a period feel, Asimov's ability to think himself into the dread his sun-soaked characters feel at the approaching gloom, their delight at the unveiling of Saro University's latest developments in light-emitting technology still rings true. But he's even better at imagining just how far the universe can exceed our expectations.

One of the younger astronomers brings up the purely theoretical case of life on a planet with only one sun, a planet where "the exact nature of the gravitational force would be so evident" astronomers would discover it "before they even invented the telescope". It's a "pretty abstraction", but only of philosophical importance, he continues: "life would be impossible on such a planet. It wouldn't get enough heat and light, and if it rotated there would be total darkness half of each day. You couldn't expect life – which is fundamentally dependent on light – to develop under those conditions." He also dares to suggest the fantastical notion that the stars spoken of in the Book of Revelations might simply be "other suns in the universe", far enough away to be invisible during Lagash's perpetual day, to leave the complicated gravitational dance of its six companion stars unperturbed. Maybe there might even be as many as "a dozen or two".

It is this kind of of mind-stretching celestial inversion which made "Nightfall" an instant classic. Campbell upped the 21-year-old Asimov's fee to a princely 1.25 cents a word and gave him the cover. "I was suddenly taken seriously," Asimov says, "and the science fiction world became aware that I existed." The science fiction world had shifted, had rolled inexorably on, powered by one of those great stories which – like the great science that underpins it – can make the planet move under your feet.